P0562: system voltage low

P0562 means the electrical system voltage the engine computer is seeing is below what it expects. Usually that is a tired battery or an alternator on the way out. It matters more than it looks, because low voltage makes other modules misbehave and store faults of their own. Diagnose soon and drive gently. Indicative UK repair cost is £40 to £400.

This is the code that explains other codes. If a scan has come back with a long and alarming list covering systems that have nothing to do with each other, and P0562 is in among them, there is a good chance it is the reason for all of it. Control modules are designed to work within a voltage window. Take them below it and they do not fail cleanly; they produce implausible readings, drop off the network, and log faults that describe symptoms rather than causes. Fixing the supply makes most of that list disappear.

Can I drive with P0562?

Diagnose soon, drive gently. The practical risk is simply not starting again, and that risk grows with cold weather and short journeys. If the charging system is genuinely not keeping up, every trip is drawing the battery down further and there is a morning coming when it will not turn the engine over. Keep an eye on whether anything else is behaving oddly, because a car running on low voltage can also be a car whose power steering assistance or stability control decides to take itself offline without much warning.

What P0562 means for your MOT

Three routes, and one of them is more practical than regulatory.

  • The lamp. Major defect, under section 8.2.1.2 of the DVSA MOT inspection manual on a petrol car first used from 1 July 2003, or section 8.2.2.2 on a diesel first used from 1 July 2008.
  • Whatever else low voltage has upset. This is the one that costs people a retest. If the anti-lock braking warning device comes on because its module is unhappy about the supply, section 1.6 of the manual fails the car for a warning device showing a system malfunction, and also for one that is not working at all. That is a separate major defect under a separate section, and it is nothing to do with your brakes.
  • The car has to run. An emissions test needs an engine running at a raised speed for long enough to take a reading. A car that will not start on the forecourt, or that dies partway through, gives the tester nothing to record.

What usually causes it

  1. A weak battery. The commonest answer, and the one most often misdiagnosed as an alternator. A battery that has lost capacity can still show a reasonable voltage at rest and collapse the moment it is asked to do anything.
  2. A failing alternator. Either the alternator itself or its regulator. The signature is charging voltage that never reaches where it should, regardless of engine speed or electrical load.
  3. Corroded earths or battery terminals. Cheap, common and frequently overlooked. A connection with resistance in it drops voltage before it ever reaches the module doing the complaining, so everything measures low while both battery and alternator are fine.
  4. A slipping or glazed drive belt. An alternator that is not being turned properly cannot charge properly. A belt that squeals on a cold damp morning, or a tensioner that has given up, belongs on this list.

What it costs to fix in the UK

£40 to £400. Cleaning terminals and earth points costs almost nothing. A battery is the lower middle. A belt and tensioner is the middle. An alternator is the top, and on engines where it sits low down behind other components the labour takes it to the upper end on its own.

Many garages and parts shops will test a battery and charging system free of charge, which makes this one of the few codes where you may not need to pay for a diagnosis at all. If you do, what a car diagnostic costs in the UK gives you the comparison.

These are indicative UK ranges for guidance only. Actual causes and prices vary by vehicle, and a stored code points to a system, not always the exact part.

What to check first

  1. Measure the battery at rest, after the car has stood. A healthy, fully charged 12 volt battery sits around 12.6 volts with everything switched off and the car untouched for a few hours. Noticeably below that and you have a battery that is either discharged or past its useful life.
  2. Measure it again with the engine running, at idle and at about 2,000rpm. Charging voltage should typically sit somewhere around 13.8 to 14.4 volts. Low at idle but correct at 2,000rpm points at the belt or at an alternator struggling under load. Low at both points at the alternator, its regulator, or the wiring to it.
  3. Check for voltage drop across the earth strap and the battery terminals. Measure across the connection itself rather than at either end. Anything more than a fraction of a volt there is resistance that should not exist, and it is the cheapest fault on this page to put right.
  4. Then re-read the codes. Fix the supply, clear everything, drive the car and read it again. The list that comes back the second time is the real list, and on a car that was running low on voltage it is usually a great deal shorter.

Related codes

Get it narrowed down before you spend

A stored code tells you which system is unhappy, not which part has failed. If you want it narrowed down before you spend anything, send the code and your symptoms and a mechanic will read them personally. Quick Diagnosis is £20, and if we can't help, you don't pay.

Written by the First Diagnostic mechanic. Over a decade in the trade: a VW-only workshop running diagnostics and electrical repair, then BMW-only through to full engine rebuilds. Now an independent all-makes workshop, plus building and wiring drift cars for competition, including trackside work as head mechanic. More about who reads your codes.