Why an EV still has a 12V battery, why it goes flat, and what owners have found actually helps. Owner reports with a link to each source — not MG statements, and not advice.
← All MG4 learningsYour rights & escalating a dispute
Why an EV still has a 12V battery, why it goes flat, and what owners have found actually helps
An MG4 with a full traction battery can still be completely immobile because a separate small 12V battery is flat, and that surprises people every time. The entries below cover the drain itself, the symptoms that come before it, and what has and has not worked - including cases where a replacement battery was fitted and the drain came back, which points at the cause being something else.
Scope. Reported across the range; more common on cars left parked for long periods.
68 reports · 23 safety-related
After any 12V disconnect, have the one-touch windows and the steering-angle sensor re-learned - with the wheels straight for the steering reset - before you drive, or the car can flag steering and driver-assist faults.
Wiki, 2022-2026GeneralMG4 2022–2025, all variants
MG's own guidance covers what happens with a badly discharged 12V battery: below about 11 volts the acid has weakened to nearly water, internal resistance is high, and at the start of charging it can look as though the battery is refusing to accept anything. As charging continues the electrolyte strengthens and the current comes back up. So do not condemn a battery in the first few minutes. MG gives limits worth knowing too: do not charge below 0 degrees, stop if the battery rises above 40 degrees, and never charge a battery whose case is bulged, cracked or leaking or whose terminal post is broken - replace it instead. Charging is effectively finished when the current falls below about 2 amps. MG also notes that a battery can be checked with a common aftermarket tester such as a Midtronics unit, but that readings from a tester of the wrong type should not be used to judge it.
2023GeneralFirst-generation MG4 12V lead-acid battery care; general vehicle fact, UK/EU document. all variants
The airbag module watches itself continuously and lights the dashboard warning lamp for anything it does not like, including a supply voltage that simply falls outside its accepted range. MG states plainly what the lamp means: while it is on, the restraint system may not operate in a crash. Two things follow for MG4 owners. First, given how often these cars suffer weak or flat 12V batteries, an airbag light is worth checking against battery health before assuming an expensive airbag fault. Second, an airbag light is never something to leave until the next service, because seat belt pretensioners and every airbag are on the same watch list. The car stores a code either way, and a fault that clears itself still leaves the code behind for a technician to read.
Jul 2023GeneralAll MG4 variants; airbag control module self-monitoring
Park on an MG4 is not a lever position. A small electric motor drives a pawl that locks a toothed gear on the drive unit's input shaft, so when the car is in P the rear wheels are held through the gearbox. MG's manual carries a dedicated 'P gear unlocking' procedure for the cases where the car will not come out of P at all: a flat 12V battery, a failed electric parking module, a high-voltage system that is down, or a shift controller that has lost communication. It is not a roadside fix. The high-voltage service disconnect has to be pulled, the underbody deflector taken off, a sealed vent plug prised out and thrown away, and a special tool wound clockwise inside the housing until the pawl clears. MG says the car needs to be supported on a jack while this is done, and that if you meet real resistance you must stop immediately or you will wreck the parking mechanism internally. The sting is the caution at the end: once 12V power is restored, the car simply shifts itself back into P. Where the problem is only a communications fault, the alternative is a dealer scan tool running the parking module's travel self-learn, which finishes with the pawl out of P. The practical upshot for an owner or a recovery driver is that a dead MG4 does not become freewheeling because someone found a lever, and getting the wheels turning again is a workshop operation rather than something done in a car park.
Jul 2023GeneralAll first-generation MG4 drive units documented in the July 2023 service manual; workshop procedure with owner and recovery consequences.
Plenty of MG4 owners keep a charger or maintainer on the 12V battery, and MG's manual sets out its own limits for doing it. Do not charge the battery below zero degrees. Stop charging if the battery itself rises above forty degrees, and wait until it has come back to room temperature. If the case is cracked, leaking or bulged, or a terminal post is broken, the battery is to be replaced rather than charged - find out why first. Clean the oxide off the posts and grease them before connecting. Connect the positive lead first and disconnect the negative first. And when the battery is still in the car, put the charger's negative clamp on a good body earth point rather than the battery's negative post, because the car's current sensor lives on that post and bypassing it leaves the car with a wrong idea of its own battery.
Jul 2023GeneralAll first-generation MG4 with the standard maintenance-free 12V battery.
MG treats "vehicle cannot be powered on" and "vehicle emergency power-off" - the car cutting its high-voltage system while you are using it - as the same fault family, with an identical six-step list. It starts with physical things: the manual service disconnect being damaged or poorly connected, then a blown fuse in the power electronic box, then the high-voltage interlock circuit, then a high-voltage insulation test, then the high-voltage and low-voltage harnesses and their connectors, and only at step six the 12V battery being flat, damaged or aged. The takeaway for an owner is that a dead or self-shutting MG4 is, in MG's expectation, a connection or a fuse rather than a failed battery or motor - but it is high-voltage work and not something to poke at yourself.
2022GeneralMG4 failing to power up, or shutting its drive system down in use all variants
An Australian owner logging the 12V battery over eighteen months recorded a range of 12.4 V at the low end to 14.3 V at the high end, with another confirming 14.4 V while actively charging. The rule of thumb owners use is around 14 V when the car is running and charging the 12V, and 12.4 to 12.6 V at rest. A resting reading of 12.2 V is already low rather than borderline. Given how many MG4 problems trace to the 12V, a cheap voltmeter is a worthwhile thing to own.
Apr 2025AUMeasured on Australian cars; applies across the range all variants
A flat 12V battery leaves the car unresponsive to the key fob, and one owner discovered the practical sting in that: the boot is effectively impossible to open when the 12V is dead, and the jump pack was inside it. Keep any jump starter, and anything else you would need in that situation, in the cabin rather than the boot. This is worth sorting out before you need it, because the moment you need it is the moment you cannot get to it.
Jul 2024GeneralReported on MG4 generally; variant not distinguished
An Australian owner's two-year service on a car with only 9,600 km on it surfaced several faults together: an intermittent boot lock failure, an airbag warning light, and charging warning lights. Low kilometres do not mean nothing has gone wrong, and on this car a cluster of electrical warnings appearing together is more often one underlying cause than several independent ones. Worth having a proper diagnostic rather than treating each warning separately.
2026AUOne Australian car at its two-year service; variant not stated all variants
An Australian owner whose front passenger window stopped working resolved it by disconnecting and reconnecting the 12V battery, and reported that the car's settings survived the reset. That is worth knowing before authorising any diagnosis of a window motor or switch: an electric window that has simply stopped responding may be a module that has latched into a bad state rather than a mechanical failure. Note that on cars with automatic windows a 12V disconnect can require the window end positions to be relearned afterwards.
May 2025AUReported on an Australian car; variant not stated all variants
An Australian owner with multiple flat 12V batteries over two months found the cause was not the battery at all: a faulty gateway module was drawing current continuously. The module was replaced under warranty and the problem stopped. This is worth knowing because the instinctive response to a repeatedly flat 12V is to replace the battery, which in this case would have solved nothing and cost money. If yours keeps going flat with nothing obviously plugged in, ask the dealer to measure the parasitic draw rather than accepting a new battery as the answer.
Dec 2023AUOne Australian car in 2023; variant not stated all variants
Don't leave the car parked for weeks with the traction battery near empty - the owner's manual states that intelligent charging of the 12V is suspended when the high-voltage battery is at a low state of charge, so the 12V can go flat.
Mar-May 2026UK/EUall MG4; thread is in the XPOWER forum but the mechanism is common to the range
If the car is going to sit parked, leave the high-voltage pack above about 50%, because the owner's manual states the intelligent 12V charging function is suspended when the HV battery is at a low state of charge.
Mar–May 2026Generalall MG4 variants (thread covers MG4 XPOWER and MG4/MG5); not market-specific
MG4 owners in the UK and other markets do report the 12V battery going flat while the car is parked, so if yours will sit for more than a week, use a trickle charger or take it for a periodic short drive.
Jul 2025UK/EUall MG4 variants; reported across UK and other markets
The tailgate is electrically released, so a flat 12V can leave the boot virtually impossible to open - keep your jump pack in the cabin rather than locked in there.
Jul 2024UK/EUall MG4 variants
Budget on an early 12V replacement: the car leaves the factory with a small ~45Ah flooded lead-acid battery in the 063 case size, and MG EV owners report flat batteries and short lives.
Jul 2024GeneralMG4 and other MG EVs, all markets
Owners collecting cases together identified four recurring causes. A genuinely defective 12V battery that no longer holds charge is only one. The others are a charging system not topping the 12V up properly, which dealers address with a software update; the car being left unused for over a month; and parasitic drain from things owners added themselves, most often dashcams and plugged-in diagnostic dongles. Before replacing the battery, work out which of the four you have, because three of them are not fixed by a new battery.
Jul 2024GeneralReported across MG4 trims; variant not identified as a factor all variants
MG's programming and configuration manual states that after replacing either the 12 volt battery or the electronic battery sensor, a write battery ID operation must be performed with the dealer diagnostic system. The manual uses the word must. The same section also notes that after the car is powered down it needs to stand for at least four hours before the system can read accurate battery status information.
Jul 2023GeneralDocumented for the MG4 generally, so all variants are listed
MG says this twice in its own words: when charging the 12V battery in the car, or jump starting, the negative lead must go to a good body grounding point rather than the battery's negative terminal. The reason is the electronic battery sensor clamped onto that negative post - it measures every amp going in and out so the car can work out the battery's state of charge and health. Clamp onto the post itself and the current bypasses the sensor entirely, so the car never sees the charge you just put in and its battery calculation goes wrong. The consequences are the annoying kind: nuisance warnings, an odd state-of-charge estimate, and the car managing its power-saving strategy on bad data for a while afterwards.
2023GeneralFirst-generation MG4 12V system; procedural fact about the car, not market-specific. all variants
The MG4 carries an electronic battery sensor bolted to the negative terminal, reporting voltage, current and temperature over a LIN bus so the car can shed loads before the battery gets too flat. MG states that once that sensor has been refitted it takes at least four hours before it has accurate status information, and adds a useful tip: for electrical work, disconnect the negative cable at the sensor rather than pulling the whole clamp off the battery post, because then the sensor keeps its picture and settles again much faster. MG also warns not to remove the sensor from the negative cable at all except when replacing the battery. The practical upshot is that immediately after a battery change or a disconnection you should not read much into what the car says about its 12V system.
2023GeneralFirst-generation MG4 electronic battery sensor; procedural fact about the car. all variants
The combined charging unit does two separate jobs. Plugged into AC, it filters, rectifies and converts mains power into high-voltage DC for the traction battery. While driving, it steps high-voltage DC down to 12 volts to run the car's electrics and charge the 12V battery - it is the MG4's equivalent of an alternator, and there is no separate one. That matters when you are chasing a repeatedly flat 12V battery: as well as the usual suspects, this unit is part of the circuit that is supposed to be charging it, so it belongs on the list of things a dealer checks rather than being ignored while a third new battery is fitted. It also explains why the 12V is only being replenished while the car is awake, driving or charging, not simply because it is parked in the sun.
2023GeneralFirst-generation MG4 high-voltage charging architecture; general vehicle fact. all variants
The interior lighting is run by the body computer rather than by simple door switches, and it has a battery-saving cutout built in. If a door is left open, the lamps fade out after 15 minutes once the energy-saving function is active. The same 15-minute limit applies to the courtesy delay after you switch the car off. There are shorter timers on top of that: unlock the car and the reading lamp comes up but fades again if no door is opened within 30 seconds, and locking the car or arming the alarm kills the delay immediately. This is genuinely reassuring in the context of the MG4's reputation for flat 12V batteries - a door left ajar overnight will not sit there burning the lights until morning. It also means the boot light is no good as a work light if you are doing anything that takes a while.
Jul 2023GeneralBody control module interior lighting logic, first-generation MG4. all variants
U1562 and U1563 mean the module's own power supply voltage is too high or too low, and they are the only two codes MG defines in all 23 modules of the car. If a diagnostic read comes back with those codes scattered across the whole vehicle, that is not 23 broken modules. It is one supply problem - most often a tired or flat 12V battery, a charging fault, or a bad earth - being noticed independently by everything on the car. It is worth knowing before anyone starts quoting for control units, because the modules are among the most expensive parts on the car and the 12V battery is among the cheapest.
Aug 2023GeneralAll first-generation MG4.
MG has a named symptom for the 12V supply failing to be topped up, and the running order it gives technicians is telling: look at the charging unit's external condition, then its coolant pipes and clamps, then the charging unit's fuse, then the wiring between the charging unit, the fuse box and the battery, and only then the charging unit itself. The 12V battery does not appear anywhere in that sequence, because in this car the same unit that charges the traction battery from the wall is what keeps the 12V topped up. If your 12V keeps going flat and a new battery has not fixed it, this is the chain MG expects a workshop to follow - and it means a single blown fuse or a coolant leak around the charger can leave you with a car that flattens its 12V no matter how much you drive it.
May 2022GeneralMG's 'Low-voltage Battery Feed' symptom diagnosis for the first-generation MG4; UK/EU document but describes car behaviour, not dealer process. all variants
MG carries a symptom called low-voltage battery feed under the Combined Charging Unit chapter, and its expected causes are, in order: visible damage or ageing of the components, the unit's external coolant pipework, the charging unit's fuse, the harness running from the charging unit through the fuse box to the battery, and finally the charging unit itself. In other words, when the 12V battery is not being kept topped up, MG does not start at the battery - it starts at the device that is supposed to be feeding it. If you have replaced a 12V battery and it has gone flat again, this is the chain to ask about by name, along with the fuse and the harness between the unit and the battery, rather than accepting a second battery.
2022GeneralUK/EU service volume; describes the vehicle's charging architecture, general to the model. all variants
Buried in the electrical inspection guidance is a number that matters to anyone chasing a flat 12V battery: MG states the car usually takes three to ten minutes to enter its sleep state fully. It also lists what has to be true for the car to be genuinely asleep - start switch off, key away from the car, accessory power off after the driver's door has been opened and closed, all doors shut, headlamps off with auto headlamps disabled, any delay lamps extinguished, the climate system off, and no scan tool talking to the car - then a further wait before any reading is meaningful. If you or an auto electrician are measuring parasitic drain on an MG4, testing before the car has been left undisturbed for that long will produce a scary number that means nothing. It also explains why the car is still doing things - fans, lamps, modules - for several minutes after you have walked off.
2022GeneralMG4 EV first-generation; vehicle sleep behaviour, not market specific all variants
The 12V battery has its own line in the exceptions table: 12 months for cars registered after January 2017, with a footnote limiting every 12V battery claim to a maximum £100 payout. Given how often an MG4's 12V battery is the thing that leaves you unable to open the boot or wake the car, that is worth knowing before you argue with a dealer - the cover is short and the money is capped, so a claim is only ever a contribution. It also means a flat 12V that traces to something else drawing current, rather than to the battery itself, is the better claim to pursue, because the module at fault is covered on the normal warranty terms rather than on this capped line.
Oct 2021UK/EUUK 12V battery warranty term and payout cap; differs from the Australian term. all variants
This is the clause that matters most to anyone with a recurring problem - and on an MG4 that usually means a 12V battery that keeps going flat. The terms give the AA the right to refuse service where it is asked to deal with the same or similar fault it already attended within the preceding 28 days. More than that, if the AA believes the cover is being over-used for a fault it has attended before, it will report the matter to MG, and MG then decides whether any further assistance is provided until a permanent repair has been carried out. The booklet also puts the obligation on you: where a patrol carries out a temporary fix, it is your responsibility to get the car to an MG Service Partner and have it made good properly. The practical lesson is that a jump start is not a solution. If the car has stranded you once, get the underlying cause diagnosed and recorded in writing straight away, because the second and third call-outs are not guaranteed.
Apr 2019UK/EUUK MG Assistance clause; the mechanism is generic to breakdown cover but the wording quoted is UK-specific. all variants
If you are leaving the car for weeks, UK owners relay an MG technician's advice to store it above 50% HV charge and to switch it on for about 30 minutes once a week so the DC-DC converter tops the 12V back up.
May 2026UK/EUall 2023 MG4 variants
If your 12V keeps going flat, look at your wallbox: one UK owner found both his MG4 and his ZS EV down to about 3V on the 12V after overnight sessions on a GivEnergy charger.
May 2024UK/EU2023 MG4 on smart wallboxes with always-on handshake
Owners on the UK forum rate flat 12V batteries among the most common MG4 gripes, and the culprit is a budget size-063 lead-acid of only about 45Ah, small for the job.
Mar–Apr 2023UK/EUall MG4 variants
After using wired Apple CarPlay, UK owners report a repeating 'USB disk identification failure' banner, sometimes followed by the radio dying and a 12V drain - one car went flat after about 2.5 days parked.
Sep 2023 - May 2024AU+UKall 2023 MG4 using wired CarPlay
However long the vehicle warranty runs, the 12V battery is covered separately and much more briefly: owners report 24 months with unlimited kilometres, and only for manufacturing defects. A 12V that has been flattened by a parasitic drain, or that has simply aged, is not a manufacturing defect. Given how many MG4 problems trace back to the 12V, it is worth knowing that this is the one component where you are on your own soonest.
Apr 2025AUAustralian warranty terms as reported by owners; applies across the range all variants
One worry with any aftermarket electronics is a parasitic 12V drain. An owner who fitted a DSP amp, powered directly from the 12V battery through an inline fuse rather than tapped from the fusebox, reported no change in the car's energy use and came back after a month away to find the battery still at the 80% he had left it. A properly wired install did not appear to add standby load.
Aug 2024GeneralBattery-fed, inline-fused DSP install showed no standby drain after a month parked
An owner wiring a dashcam into the cabin fuse box (Dec 2022) found fuses he expected to be ignition-switched did not power off: after locking the car and walking away, LEDs on that circuit were still lit fifteen minutes later, and another poster explained that EVs commonly bring circuits live with the ignition off. He planned to move to the top-left fuse feeding the USB ports and wireless charger instead, expecting that one to drop at lock - but posted no test result, and another member pointed out USB outlets run at 5 V while the fuse box is 12 V. Measure with a meter before you commit, and use a hardwire kit with a low-voltage cutoff rather than trusting the fuse label.
date not establishedGeneralAny MG4 having a dashcam or other accessory hardwired into the cabin fuse box. all variants
MG fits a Crash Power Module on the driver's side of the car, wired in series between the 12V battery and the body control module. It is a supercapacitor: it holds enough energy to run the body control module's unlock function even if the battery or its cable is destroyed in a collision, so the doors can still be released and people can get out or be got out. This is the documented mechanism behind the assurance that an MG4's doors unlock after an impact despite there being no mechanical emergency release on the inside handles - it is in MG's own description of how the car is built, not an inference from a crash test result.
2023GeneralFirst-generation MG4 low-voltage supply architecture; hardware fact, not market-specific. all variants
Two lighting conveniences MG documents that most owners never find. Follow Me Home keeps the dipped beam and side lights on after you shut the car down so you can see your way to the door; the duration is settable from 0 to 90 seconds in 30 second steps, opening a door restarts the timer, and it can be triggered manually by pulling the light stalk toward the steering wheel after the car is powered off. MG notes it will not work if the 12V battery is over-discharged. Separately, once the car has been locked for a few minutes, a vehicle locating function arms itself: press LOCK on the remote key and the car signals its position, either lights only or lights plus horn depending on the setting. Pressing LOCK again turns it off, and pressing UNLOCK cancels it.
2023GeneralLighting convenience functions from MG's UK/EU training material; menu availability can vary by trim and software version. all variants
MG splits a tailgate that will not release into two separate complaints - it will not open from the switch on the car, and it will not open from the remote key - and they run through different parts. On cars with the power tailgate the routine checks the power tailgate fuse early in both, then the release switch and its wiring, the left power tailgate support rod, the tailgate lock body, the power tailgate control module, and only last the body control module. Keyless opening at the boot is listed separately again and depends on an antenna in the rear bumper. So if your boot opens on the key but not the button, or the other way round, that is a diagnostic clue rather than a mystery, and it points at the switch or key side rather than the latch. A fuse and a tired support rod are both on MG's list ahead of the expensive modules, which is worth raising before a control module is quoted, and if keyless boot opening stopped after rear-end body work, the bumper antenna is the thing to check.
2023GeneralTailgate release diagnosis from MG's UK repair information; power tailgate content applies only to cars fitted with it. all variants
MG's own removal procedure for the driver's door describes a lock cylinder mounted in the outer handle, reached by removing a small plug at the rear edge of the door, with a mechanical link rod running from the cylinder to the door lock. The outer handles on both front and rear doors also work the latch through a physical link rather than purely electrically. This matters when the 12V battery is flat: the emergency blade key inside the fob has somewhere to go on the driver's door, and the mechanism it operates is mechanical, so it does not depend on the car having power. It is the counterpart to the well-known problem that a flat 12V leaves you unable to open the boot at all.
Jul 2023GeneralDriver's front door on keyless-entry cars; blade key lives inside the fob all variants
MG has a symptom chart headed manual tailgate release failure, meaning a boot on a car without the powered tailgate that will not open. The second thing it tells the technician to do is swap the tailgate release switch for a known-good one, and the third is to work through that switch's wiring and connectors. So even the basic tailgate is opened by pressing an electrical switch that asks the car to unlatch, rather than by any handle that pulls the latch directly. That is the underlying reason a car with a flat 12V battery leaves you locked out of your own boot, which is exactly why owners warn against storing a jump pack in there.
May 2022GeneralMG's diagnosis for a non-powered MG4 tailgate that will not open; UK/EU-published manual, partial page. all variants
MG's procedures for the tailgate failing to open, whether you press the switch or use the remote key, both put a fuse check near the top: the power tailgate fuse, on cars fitted with a powered tailgate. After that come the release switch, the lock body, the left power tailgate support rod - the strut on that side is the powered unit - then the tailgate control module and finally the body control module. So a powered boot that has gone completely dead is worth a fuse check before anything else, and a boot that unlatches but will not lift itself points at that left strut rather than at the electronics. Every path MG lists is electrical, which is consistent with owners finding the boot unopenable when the 12V battery is flat.
May 2022GeneralMG's cause list for a tailgate that will not release, switch or key; UK/EU document, powered tailgate fitment varies by trim and market. all variants
The exclusion is blunt: attendance or payment for lost or stolen keys, or when keys have been locked in the vehicle, is not covered. Keys are also named alongside petrol and consumables in the list of things the cover will not buy. If a locksmith is needed the AA will try to arrange one, but will not pay, and the contract for that work is between you and the locksmith. There is a sting in the tail as well - once a locksmith or other specialist would, in the AA's view, get the car mobile again, no further service is available for that breakdown, so you cannot fall back on a tow instead. On a car with keyless entry, a digital phone key and a boot that will not open when the 12V is flat, this is worth knowing before you need it: a spare key kept somewhere sensible is cheaper than an emergency locksmith.
Apr 2019UK/EUUK MG Assistance exclusion list; Australian roadside terms not described by this document. all variants
MG explains that the sensor identity codes are stored in the body control module and survive a power cut, but the live pressure values do not: after the module loses power or the 12V battery is disconnected, all four wheels display dashes. The sensors sleep when the car is parked, so nothing arrives until the wheels are turning. Drive at 40 km/h (25 mph) or above and each sensor switches to rolling mode, transmits, and the display fills in. There is a stationary alternative too - deliberately dropping a tyre's pressure by more than 30 kPa makes that sensor wake and report. So blank pressure readings after battery work are expected behaviour, not a fault and not a workshop job.
2023GeneralFirst-generation MG4 TPMS behaviour; general vehicle fact, UK/EU document. all variants
On the rear axle the parking brake is an electric motor built into the caliper, so the piston cannot simply be wound or pressed back the way a front one can. MG's own procedure is to command the parking brake to retract with a diagnostic tool, disconnect the 12V negative, change the pads, reconnect, and then use the tool again to adjust the parking brake before the car is driven. Replacing the parking motor itself adds a further initialisation step. Two things follow for an owner. A workshop that cannot talk to the MG4's brake module cannot correctly do rear pads, whatever it says about the job being ten minutes a side. And because the job disconnects the 12V battery, you inherit the usual after-effects of that: blank tyre pressure readings until the car has been driven, and a 12V system that takes hours to work out its own condition again. Front pads need no tool at all.
Jul 2023GeneralApplies to all first-generation MG4s; the manual is the UK/EU July 2023 issue but the hardware is not market-specific
Each of the MG4's four tyre pressure sensors carries a unique identity that tells the body control module which corner it is sitting on, and the module - not a separate TPMS box - is what reads them. MG's procedure after fitting a new sensor is an explicit self-learning routine performed on the body control module with diagnostic equipment; the car does not work it out for itself. So if you buy a second set of wheels, replace a sensor after a puncture, or let a tyre shop fit a cheap aftermarket sensor, ask first whether they can carry out the MG self-learn, or you may get the car back with a permanent warning light or a corner that reads dashes. A related quirk from the same section: cutting the 12V power keeps the sensor identities but wipes every stored pressure, which is why the display shows dashes after battery work until the car has been driven.
Jul 2023GeneralTyre pressure sensor replacement; general to the car all variants
The high-voltage components on this car are linked by an interlock loop that proves every high-voltage connector is properly mated. MG lists the loss of that signal as its own symptom, with the consequence stated plainly: high-voltage power cannot be supplied to the vehicle. The car will not drive and will not charge, and the causes MG expects are a damaged, corroded, deformed or poorly mated high-voltage connector at the charging unit, a fault inside that connector's interlock circuit, or the unit itself. MG's own procedure begins by isolating the pack with the manual service disconnect before anything is touched. For an owner this is a car that appears completely dead in the drivetrain despite a healthy 12V system and no obvious damage - and it is a plausible consequence of underbody impact, flooding or badly done work under the car. It is emphatically not a DIY investigation.
2022GeneralUK/EU service volume, in the Combined Charging Unit chapter; the interlock principle applies to the model generally.
Measured by an Australian owner, the supplied portable charger pulls roughly 1.2 kW rising to about 1.6 kW as the 12V battery finishes topping up. That is a genuinely slow rate: it will add perhaps 8 to 10 kWh overnight, which is fine for a short daily commute and nowhere near enough to recover a big battery from low. If the granny charger is your only option, the 51 kWh car is a much easier proposition than the 77.
2025AUMeasured on an Australian car with the supplied portable charger all variants
MG's own description of the high-voltage layout makes the split explicit. Slow AC charging goes in at the charge port, through the combined charging unit which converts it, then on to the high-voltage distribution unit and into the pack. DC fast charging bypasses the charging unit entirely and runs from the port through the distribution unit straight to the battery. Two things follow for owners. A fault in the onboard charging unit can leave a car that rapid-charges faultlessly but will not take a wallbox or a granny lead at all - and the reverse pattern points instead at the distribution side or the pack. It is worth saying out loud at the service desk, because a technician who plugs into a rapid charger, sees it work and hands the car back has not tested the AC hardware at all.
Jul 2023GeneralAll first-generation MG4; describes the physical high-voltage architecture, not a market option.
The charge brick supplied with Australian MG4s draws a maximum 8A (1.84 kW at 230V) and its current is not adjustable, so owners report only about 1.2-1.6 kW actually reaching the drive battery.
Oct-Dec 2024AUAustralian-delivered MG4 (the AU-supplied charge brick) all variants
When charging from a household socket, roughly 1.7 kW at the wall becomes about 1.5 kW into the battery, with around 200 watts going to the onboard charger and battery management rather than into the pack. Because the overhead is roughly constant, it hurts proportionally more the slower you charge. Over an eight hour overnight session you may add 12 kWh to the battery while paying for 14 or 15. It is not a reason to avoid the granny charger, but it is worth knowing your electricity bill will not match what the car says it received.
Feb 2024AUMeasured on an Australian car with the supplied portable charger; applies across the range all variants
The high voltage precautions name the components that untrained staff are forbidden to dismantle, and the list is broader than owners expect: the battery pack and drive motor, the power electronics, the high voltage harness, the electric air conditioning compressor, the onboard charger, the charging port and the AC charging cable. Work requires documented high-voltage training, insulating gloves and boots to a national standard, and a multimeter check that the circuit is genuinely dead before anything is touched. After the manual service disconnect is pulled, a five minute wait is required before checking for residual voltage, and the car must stand for at least three minutes with the 12V and redundant 12V batteries disconnected beforehand. The practical consequence is that a damaged charge port or charging cable is not a general workshop job on this car, and a repair done outside that framework is both a safety question and a warranty one.
2022GeneralMG4 EV first-generation; high-voltage system scope, licensing wording is source-market specific all variants
An Australian owner who needed recovery reported MG's roadside assistance providing a tow but described the handover process as slow, with the truck taking 60 to 90 minutes to arrive. That is not unusual for roadside recovery generally, but it is worth calibrating expectations, particularly if the reason you are stranded is a flat 12V and you are somewhere exposed. Knowing that a jump pack in the cabin would have saved the wait is the practical takeaway.
2026AUOne Australian owner's experience; applies across the range all variants
One UK owner had three updates applied in one March 2025 visit — lane keep assist, charger pin and immobilisation — and the immobilisation one failed on the first attempt. After it was reapplied the car showed power being delivered but would not move and could not be shifted to neutral for towing; the dealer found the rear wheels locked and needing a special key from MG to release. A week later the car was still in, with no courtesy car and no communication, and the thread records no resolution. Experienced owners note a scrambled module usually has to be programmed as a replacement, not re-updated.
Mar 2025UK/EUAny MG4 having several module updates flashed in a single visit all variants
Three of the MG4's most expensive charging-side parts are explicitly not plug-and-play. The manual ends the battery pack refit by requiring the battery management system to be programmed and coded, and says the pack is only fitted to the car after that succeeds. The combined charging unit (the box that handles AC charging and also feeds the 12V system) and the electric vehicle communication controller each get the same instruction. There is also a step before the pack's own electronics module comes out: the diagnostic tool is connected first to back up the parameters held in the battery management system. The practical consequence for an owner is that a second-hand or salvage part cannot simply be bolted in - it needs MG's tool and the right file - and that if charging misbehaves after a big repair, an omitted coding step is a fair thing to ask about.
Jul 2023GeneralMG4 EV, first-generation; applies to HV battery pack, combined charging unit and EV communication controller replacement all variants
MG's own fault-code list runs to 1,171 codes across 23 modules, and 222 of the entries are some version of 'lost communication with' another module, plus another 42 for the network dropping out entirely. Those codes do not mean the module that reported them is broken. They mean it could not hear something it expects to hear. One flat 12V battery, one disturbed connector, or one genuinely dead module will light up ten or twenty of them at once right across the car. If a workshop reads the car, hands you a list of fifteen faults and quotes accordingly, the right question is which one of them is the cause and which fourteen are just the rest of the car noticing. MG's own manual is organised the same way, with a whole separate procedure for checking the integrity of each network before chasing any individual code.
Aug 2023GeneralAll first-generation MG4. Counted from MG's own fault-code index for the 23 modules it documents.
The manual opens the diagnostic system check with a list of conditions that must all hold before any of its procedures are valid: the 12V battery fully charged with clean, secure cabling, no blown fuses, clean and correctly positioned earth points in the area of the complaint, all connectors on the suspect circuit properly seated, and explicitly no after-sale add-on equipment affecting the system's operation. In practice that means a car with a tired 12V battery, or with a dashcam, aftermarket camera, amplifier or lighting spliced into the harness, does not meet MG's own preconditions for diagnosis. Two things follow for owners. First, sorting a weak 12V battery before the visit can be the difference between a diagnosis and a wasted day. Second, be upfront about everything that has been added to the car, because MG's process expects the technician to account for it, and hiding it is the fastest way to a bill for time spent chasing your own accessory.
2022UK/EUMG4 EV first-generation; UK/EU RMI document describing MG's workshop preconditions all variants
New MG4s sold in the UK include MG Assistance, an AA-provided roadside breakdown package, at no extra cost, and there's usually a wallet-sized card in the glovebox with the number on it. It's tied to the car rather than the driver, covers breakdowns within the UK only, and owners report it turning out for punctures, flat 12V batteries and lock-outs, often within the hour. The twist several owners flagged is that having the car serviced at an MG dealer renews the cover for another year, so keeping to dealer servicing keeps the breakdown cover alive. If you already hold personal AA or RAC membership you may be double-covered; some owners asked their own provider to suspend that policy while the manufacturer cover runs.
Sep 2023UK/EUUK new-car MG Assistance (AA) breakdown cover, free, renews on MG dealer service all variants
The MG4 has no equivalent of a sentry or guard mode and no built-in recording, so if you want footage you are fitting a dash cam. Australian owners have found MG4-specific mounting options online at around $125, though some are configured for left-hand drive and need checking. Bear in mind that a dash cam wired for parked recording is one of the most common causes of a flat 12V on this car, so wire it to a switched supply or accept that it only records while you are driving.
Jul 2023AUAustralian cars; applies across the range all variants
Owners get a Vehicle Control System Fault message with a sharp drop in drive power and a loss of regenerative braking, which resolves after a few seconds when a 'Speed Limit Cleared' message appears. It has been seen both on the move and sitting stationary on a driveway, and a flat 12V was ruled out on the first car, which measured 12.7V. Three owners reported it independently over October and November 2022; one of them, 2.5 miles into a brand-new car, sat five hours at a dealer that could not identify it and was told they would have to speak to MG. Get the date and time of each event logged with the dealer so there is a record if it recurs.
Oct 2022UK/EUEarly MG4s; the transient nature makes it hard to reproduce at a dealer.
Worth knowing before anyone starts dismantling the dashboard: the MG4's head unit is mounted behind the glovebox, while the screen on the dash is effectively the display. Owners doing audio work reach the unit from the passenger side. It also means the unit is driving the standard speakers directly with no separate amplifier in most cars, which is why aftermarket speakers chosen to be easy to drive work without adding one.
Mar 2023UK/EUReported on a UK Trophy; assumed common across the range but not confirmed per variant all variants
Australian guidance from May 2025 says the MG 4's operating and infotainment systems come on as soon as the car is unlocked, and you can shut them down from the driver's seat via the Safety menu, then Vehicle Power Off.
May 2025AUall 2023 MG4, Australian market
MG documents fan control in two states. With the high-voltage system live, the fan runs if the drive-unit coolant reaches 55 degrees C or the air-conditioning pressure reaches 0.22 MPa, and it has eight speeds set by coolant temperature, ambient temperature, refrigerant pressure and road speed. With the high-voltage system switched off — that is, after you have parked and locked the car — MG still commands the fan on when the drive-unit coolant is at or above 63 degrees C, with timing given as 120 seconds when the ambient temperature is 5 degrees or above and 60 seconds when it is below. So a whirring from the front of a car you have just parked after a fast run or a DC charging session is the system dumping residual heat, not a fault and not a sign of a parasitic drain.
2023GeneralFan control thresholds from MG's UK/EU training material; these are vehicle control parameters, not market settings. all variants
MG's description of the power seat explains that each motor is fed 12V straight from the switch pack, and that when the seat reaches the limit of its travel in any direction a thermal protection cut-out drops the power automatically to save the motor. Practically, that means holding the switch once the seat has stopped achieves nothing except heating the motor, and a seat that goes dead for a while after a lot of fiddling - moving a child seat, swapping drivers, loading long items - can be the protection working rather than a failure. Worth leaving it alone for a few minutes before booking a repair, particularly since MG's remedy for a genuinely failed seat motor is to replace the assembly it lives in rather than the motor alone.
Jul 2023GeneralCars fitted with the powered driver's seat; manual seats are unaffected.
For one window that has gone dead, MG's order of investigation is worth knowing because the cheap causes come first. After a look for anything obviously jammed or damaged, step two is the power window fuse, and step three is the window regulator cable, checked for having come off its track or broken. Only after those does the manual move to the switch, then the wiring, then the motor, and finally to reflashing the body computer. The window motors are not simply switched on and off by the button either - they sit on a network that reports back to the body computer, which is why software on that module is the last thing MG looks at and why a power interruption can leave a window behaving oddly until the system re-establishes itself.
May 2022GeneralMG's documented diagnostic order for a single inoperative power window; UK/EU-published manual. all variants
After a long park the car can drop into a deep-sleep state where iSmart remote climate, preheat and defrost stop responding while lock and unlock still work; unlocking and re-locking with the key fob wakes it up.
Jan 2026UK/EUMG4 2022–2025, all variants
When iSMART says the status is unknown or a remote command fails, the usual cause is that the car has gone into a deep sleep to protect the 12V battery after roughly a day and a half of sitting untouched. The app cannot wake it from that state. What owners find works is going to the car and unlocking and relocking it with the key, then refreshing the app. If that does not restore it, MG's own support has pointed people at a telematics box reset done by an authorised workshop.
Sep 2025GeneralReported across MG4 trims; variant not identified as a factor all variants
Owners who want a real answer on battery degradation use a Bluetooth diagnostic dongle with a compatible app to read state of health directly, rather than inferring it from the range readout, which is not a capacity meter. One Australian owner reported 100 percent state of health after several thousand kilometres. The rough expectation owners work to is one to five percent loss in the first year, with ten percent in that period being cause for concern rather than normal.
Dec 2023AUAustralian owners; applies across the range all variants
A common assumption is that speakers rated for hundreds of watts must be better. But the factory amplifier only puts out roughly 18-25W per channel from a 12V supply, and high-power-handling speakers are usually less sensitive, needing more watts for the same volume. Fit them without adding an amp and you can find the maximum clean volume has actually dropped, with distortion setting in earlier on the dial. Sound quality at normal levels may still improve; you just should not expect them to go louder.
Aug 2024GeneralLow-sensitivity high-wattage speakers on the stock amp can reduce max clean volume all variants