Reductant Pump Supply Voltage Circuit Stuck On
The supply relay or driver for the reductant pump is welded or stuck active - the pump runs continuously, even with the engine off, draining the battery and over-pressurising the dosing circuit.
Affected components
- Reductant pump supply relay
Common causes
- High likelihood: Supply relay welded
- Low likelihood: Carbon or debris buildup preventing free movement
- Low likelihood: Component wear with age - mechanical play
Possible symptoms
- Check engine light or NOx warning on
- AdBlue/DEF level or quality warning
- Possible no-start countdown after ignore period
- Failed emissions inspection (NOx)
Diagnostic notes
- The malfunction indicator lamp may illuminate
- This code can affect emissions
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.