OBD Code P0562: System Voltage Low — Battery, Alternator or Earth?

What does code P0562 mean?

Code P0562 (System Voltage Low) means the ECU detected the supply voltage falling below approximately 10V for a sustained period. Normal operating voltage is 13.8-14.5V with the engine running, and 12.4-12.7V with the engine off.

Low voltage triggers a cascade of false codes across multiple modules — after fixing the charging issue, most disappear on their own.

Symptoms

• Check engine light (plus potentially many other warning lights)
• Flickering dashboard lights
• Difficult starting
• Electronics resetting (radio, windows, sunroof)
• Dimming headlights at idle

Diagnosis with a multimeter (10 min)

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1. Engine off: measure battery terminals. Normal: 12.4-12.7V. Below 12V = discharged or failing battery
2. Engine running: same test. Normal: 13.8-14.5V. Below 13V = alternator not charging
3. Rev to 2000 RPM: voltage should rise to ~14.2V. Stays flat → alternator fault

Causes

1. Failing battery (40%)

Batteries over 4-5 years old lose capacity and can't hold charge overnight.

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2. Alternator fault (30%)

Failed diode or voltage regulator. If voltage stays below 13V with engine running, the alternator isn't charging.

3. Poor earth connection (20%)

The battery negative earth cable connects to the engine block and bodywork. Corrosion creates resistance → low voltage at the ECU.

👉 Earth strap on Amazon UK — £8-20, clean or replace corroded earths

4. Serpentine belt slipping (10%)

If the alternator drive belt slips, the alternator doesn't spin fast enough to charge.

Repair cost