Will low voltage damage the PCM?

Prolonged low voltage can corrupt PCM memory and damage sensitive electronics. This is another reason to address it quickly rather than driving on it.

Why does the voltage drop only at idle?

At idle, the alternator spins slower and produces less output. When AC, lights, and the blower all run at idle, a weakening alternator cannot keep up.

My battery light is not on. Can I still have P0562?

Yes. The battery light has its own threshold, which may be lower than the PCM's threshold for P0562. You can have low voltage detected by the PCM before the battery lamp activates.

Codes › P0562

P0562: The electrical system voltage is running too low

System Voltage Low

High severityCan you keep driving?

Drive directly to a shop or home. Low voltage can cause the engine to stall or electronics to fail without warning. Do not make long trips with this code active.

What it means

P0562 means the PCM detected battery voltage below a threshold, typically around 10 to 11 volts, for a defined period. The car needs roughly 13.5 to 14.8 volts when running, supplied by the alternator. When it falls short, everything electrical is underpowered. The code is commonly set while idling with loads like AC, headlights, and blower on, when a failing alternator cannot keep up. The underappreciated trap: a loose alternator belt or a corroded battery terminal can mimic alternator failure. Check those first before condemning a $200 alternator.

Common causes

Failing alternatorCannot maintain charging voltage under load. Output drops below the threshold at idle with AC on.
Loose or worn alternator beltThe belt slips under load and reduces alternator output. Cheaper and faster to check than the alternator itself.
Corroded or loose battery terminalsResistance at the terminal causes voltage drop. Clean first; the fix may be free.
Weak or failing batteryA battery that cannot hold charge pulls voltage down, especially at cold start.
High-draw electrical faultA short or a module stuck on can drain the system faster than the alternator can supply.

What it costs

Battery terminal cleaning$0 to $30 if DIY
Alternator belt replacement$80 to $200
Battery replacement$150 to $300
Alternator replacement$300 to $700

Symptoms

Check engine light on
Battery warning light may also be on
Dimming headlights or interior lights at idle
Electrical components behaving erratically
Engine stalls or is hard to start

What to do next

Use a multimeter to check battery voltage with the engine running. It should read 13.5 to 14.8 volts. At or below 12.6 volts with the engine running, the alternator is not charging. Before replacing anything, check the belt for tension and condition and clean the battery terminals. A free battery test at any auto parts store can confirm the battery health.

Lewis shows live battery voltage from the ECU sensor so you can monitor whether voltage is dropping under specific loads or only when idling. Download Lewis.

Related codes

FAQ

Will low voltage damage the PCM?: Prolonged low voltage can corrupt PCM memory and damage sensitive electronics. This is another reason to address it quickly rather than driving on it.
Why does the voltage drop only at idle?: At idle, the alternator spins slower and produces less output. When AC, lights, and the blower all run at idle, a weakening alternator cannot keep up.
My battery light is not on. Can I still have P0562?: Yes. The battery light has its own threshold, which may be lower than the PCM's threshold for P0562. You can have low voltage detected by the PCM before the battery lamp activates.