System Voltage Unstable
The ECU monitors battery voltage and detects unstable behaviour - rapid fluctuations beyond what current load changes explain. Typical causes are a failing alternator, loose battery terminals, weak battery, or a heavy load (radiator fan, glow plugs, heated screen) drawing voltage down briefly.
Affected components
- Alternator
- Battery
- Main supply wiring
Common causes
- High likelihood: Alternator regulator failing
- Medium likelihood: Battery weak or terminals loose
Diagnostic notes
- The malfunction indicator lamp may illuminate
Sources
Diagnostic information is provided for reference only. Confirm the code with a compatible scan tool and follow the vehicle manufacturer's service procedures before replacing components.