Why do I have lots of warning lights on with P0562?

Because low voltage upsets everything. Control modules across the car are designed to work within a supply range, and below it they behave unpredictably, drop off the communication network and store their own fault codes. A car with a failing alternator will often light the ABS, stability control, power steering and airbag lamps together, none of which have anything actually wrong with them. Repair the charging fault, clear the codes, and most of those lamps will not come back.

Will P0562 fail an MOT?

Yes, on the lamp. An illuminated engine management lamp is a major defect for petrol cars first used from 1 July 2003 and diesels from 1 July 2008, with 371,859 recorded failures against it. The MOT does not test the charging system itself, but a tester will record a battery that is insecure or leaking, and a car that will not start or stay running cannot be tested at all.

Does disconnecting the battery affect the MOT?

It can, and it catches people out. Disconnecting or replacing the battery clears the stored fault codes and also resets the on-board readiness monitors, which are the self-tests the car runs on its emissions systems. A tester can see that those monitors have not completed, and on many cars the emissions check cannot be finished until they have. Getting them to run again needs a proper drive cycle, potentially up to a hundred miles of mixed driving, so leave time between any electrical work and the test.

Powertrain code · standard

P0562System voltage too low

Standard definition: System Voltage Low

Last updated 27 July 2026

Quick answer

The engine control unit has measured the car's electrical system running below the voltage it needs to work reliably. It is a charging or battery problem rather than an engine problem, and it is worth taking seriously because low voltage makes other modules behave strangely.

How the car works this out

The control unit monitors its own supply voltage continuously. With the engine running, a healthy system sits somewhere around thirteen and a half to fourteen and a half volts, and the unit knows that. P0562 is set when the measured voltage stays below a threshold — commonly around ten to eleven volts with the engine running — for long enough to rule out a momentary dip from the starter or a cooling fan cutting in. It is one of the few codes worth fixing first when several are stored, because low voltage generates spurious faults in modules all over the car.

What you might notice

Battery charge warning lamp on, sometimes alongside the engine lamp
Dim or flickering headlights, worse at idle
Slow cranking, or a car that will not start after standing overnight
Several unrelated warning lamps appearing at once
Electric windows and heater fan running slowly
A whining or squealing noise from the auxiliary belt area

What causes it

Most likely first. A code names the check that failed, not the part that failed it, so more than one of these can produce the same number.

1A failing alternator, or a worn regulator inside itCommon
How to check: Measure the voltage across the battery terminals with the engine running and the electrical loads switched on. Anything much below thirteen volts under load points at the charging system.
2A slipping, glazed or worn auxiliary belt, or a failed tensionerCommon
How to check: Look at the belt for glazing and cracking, and listen for a squeal when a heavy electrical load is switched on. A slipping belt cannot drive the alternator properly.
3A battery at the end of its life, no longer able to hold chargeCommon
How to check: A proper load or conductance test at a garage or parts shop, which most will do free. A voltage reading alone does not tell you whether a battery is healthy.
4Corroded battery terminals or a loose, corroded earth strap between the engine, body and batteryCommon
How to check: Measure the voltage drop across each connection with the engine running and the loads on. More than a few tenths of a volt anywhere in the path is a bad connection.
5A parasitic drain flattening the battery overnight, often an aftermarket accessory or a module not shutting downPossible
6A damaged main charging cable between the alternator and the batteryLess common

What to do about it

1Fix this before chasing any other code. Low system voltage makes control modules misbehave and store faults that vanish once the electrics are healthy, and diagnosing those first wastes money.
2Have the battery load tested rather than just its voltage measured. Most garages and parts chains do it free and it takes minutes.
3Check and clean the battery terminals and the main earth straps. Corrosion here is common, cheap to fix and frequently the whole answer.
4Look at the auxiliary belt. A glazed or slipping belt is one of the cheapest repairs on this list and one of the most commonly missed.
5Ask about the battery registration if the car has a smart charging system and the battery has recently been replaced. On many modern cars a new battery must be coded to the vehicle or the charging strategy will not suit it.

Can you keep driving?

Only to a garage

If the charging system has genuinely failed, you are running on whatever is left in the battery, and when that goes the engine stops — usually at the least convenient moment, taking the power steering and brake servo assistance with it. Switch off everything you do not need, avoid restarting the engine unnecessarily, and go straight to a garage rather than home by way of anywhere.

Will it fail an MOT?

The lamp is a major defect and one of 371,859 recorded failures. Two further points are specific to a low voltage fault. The MOT does not test the charging system, but the tester will record a battery that is insecure or leaking, and a car that cannot be started or kept running cannot be tested at all. There is also a trap in the aftermath: if the battery is disconnected or goes flat during the repair, the readiness monitors reset, and on many cars the emissions check cannot be completed until they have run again, which needs a proper drive cycle rather than a lap of the block.

The light this turns on

Engine management lightThe engine management system has found a fault it cannot correct and has stored a code for it. The car will usually still drive, but an illuminated engine light is an automatic MOT failure on petrol cars first used from 1 July 2003 and diesels from 1 July 2008.

Common questions

Is P0562 the battery or the alternator?: It can be either, and the quickest way to tell them apart costs nothing. Measure the voltage across the battery terminals with the engine running and the headlights, heater fan and heated rear window switched on. A healthy charging system holds somewhere around thirteen and a half to fourteen and a half volts under that load. If it does, the alternator is doing its job and the battery is the suspect, so have it load tested. If the voltage sags well below thirteen, the charging side is at fault — the alternator, its belt, or the cables and earths connecting it.
Why do I have lots of warning lights on with P0562?: Because low voltage upsets everything. Control modules across the car are designed to work within a supply range, and below it they behave unpredictably, drop off the communication network and store their own fault codes. A car with a failing alternator will often light the ABS, stability control, power steering and airbag lamps together, none of which have anything actually wrong with them. Repair the charging fault, clear the codes, and most of those lamps will not come back.
Will P0562 fail an MOT?: Yes, on the lamp. An illuminated engine management lamp is a major defect for petrol cars first used from 1 July 2003 and diesels from 1 July 2008, with 371,859 recorded failures against it. The MOT does not test the charging system itself, but a tester will record a battery that is insecure or leaking, and a car that will not start or stay running cannot be tested at all.
Does disconnecting the battery affect the MOT?: It can, and it catches people out. Disconnecting or replacing the battery clears the stored fault codes and also resets the on-board readiness monitors, which are the self-tests the car runs on its emissions systems. A tester can see that those monitors have not completed, and on many cars the emissions check cannot be finished until they have. Getting them to run again needs a proper drive cycle, potentially up to a hundred miles of mixed driving, so leave time between any electrical work and the test.

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