What it means
The reductant pump supply voltage circuit is detected as stuck on. The code alone does not establish that the pump runs continuously or that it over-pressurizes the dosing circuit.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The reductant pump supply circuit is switched so the DEF/AdBlue dosing pump receives power when needed. The control module monitors whether supply voltage drops when the circuit should be off and sets P05F1 when it detects voltage remaining on. The code does not prove that the pump is running continuously or that dosing pressure is excessive.
Common causes
Most likely first.
- Control circuit or relay stuck on
- Wiring short causing unintended power
Symptoms
- Check engine light or emissions warning may illuminate
How to diagnose it
- Record freeze-frame data and check live pump command and supply-voltage status to see whether the circuit appears powered when the pump is not commanded.
- Inspect the pump supply wiring and connectors for a short to battery positive, damaged insulation, water, or terminals bridged by corrosion.
- Check the pump relay and its socket for stuck contacts, heat damage, or incorrect wiring.
- Compare the pump command with voltage measured at the supply using the wiring diagram and the manufacturer's test procedure.
- If the voltage remains present with the relay and harness isolated as specified, test the control circuit and module output for a fault.
Common fixes
- Repair wiring shorted to a power source in the pump supply circuit.
- Repair or replace damaged or contaminated connector terminals.
- Replace a relay confirmed to have contacts stuck closed.
- Repair or replace a confirmed faulty control module output.
Can I keep driving?
The code alone does not mean the pump is running continuously, but the supply fault can interfere with DEF/AdBlue dosing and emissions control. Avoid extended driving if warnings worsen or a countdown appears, and have the circuit checked before a starting restriction develops.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.