System Voltage Low

What it means

The engine computer has detected supply voltage below the expected minimum while the engine is running. This usually means the alternator is not charging enough, the battery is weak, or there is high resistance in the connections.

Related codes: P0560P0561P0563P0620P0622

Symptoms4

• Battery light on.
• Slow cranking, or no start after the vehicle has been stopped.
• Dim lights, especially at idle.
• Some electrical devices stop working or other modules set codes.

Possible causes6

• Alternator not charging because of a fault in it or its voltage regulator.
• Broken or loose alternator belt.
• Weak or aged battery, especially in high heat.
• Corroded battery terminals or ground points.
• Blown main fuse or fusible link in the charging circuit.
• Excess electrical draw from add-on devices, or a parasitic drain flattening the battery.

How to diagnose5

1. Measure battery voltage with the engine running and compare it with the manufacturer charging specification.
2. Inspect the alternator belt and its condition.
3. Test the battery with a load tester.
4. Measure voltage drop across the positive charging cable and ground cables while running.
5. If the battery drains while parked, have a parasitic drain test done.

How to fix6

1. Clean and tighten the terminals and ground points.
2. Replace the alternator belt if broken or loose.
3. Replace the fuse or fusible link after finding why it blew.
4. Replace the battery if it fails the load test.
5. Replace the alternator if it is proven not to charge.
6. Clear the codes and confirm charging voltage with electrical loads switched on.

The cost is low when a corroded terminal or belt is to blame, and rises when the battery or alternator is replaced.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions