What it means
The control module monitors the reductant pump supply circuit and checks whether power is available when the pump is commanded on. It sets this code when the supply remains off instead of switching on as expected.
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 switches power to the DEF/AdBlue dosing pump when the control module commands it on. The module monitors the circuit response and sets P05F2 when supply voltage stays off instead of appearing as expected. This indicates a supply or switching problem, not automatically a defective pump.
Common causes
Most likely first.
- Control circuit or relay does not switch on
- Open or faulty wiring
Symptoms
- Check engine light or emissions warning may illuminate
How to diagnose it
- Record freeze-frame data and use live data to check whether the module commanded the pump on when the circuit remained off.
- Inspect the pump supply fuse, relay, wiring, and connector for an open, loose terminal, corrosion, or a pushed-back pin.
- Check battery voltage and verify that the relay has its expected power and control inputs when the pump is commanded.
- Measure the supply at the pump during a commanded-on event and compare it with the circuit diagram and manufacturer's specification.
- If supply is absent, test continuity through the relay, harness, and module control path to locate the open or switching fault.
Common fixes
- Replace a failed fuse or relay after checking why it failed.
- Reseat or repair a loose, corroded, or pushed-back connector terminal.
- Repair an open or damaged pump supply or control wire.
- Repair a confirmed module control fault if the wiring and relay inputs are correct.
Can I keep driving?
The vehicle may remain driveable, but the pump may not deliver DEF/AdBlue and emissions control can be impaired. Follow any emissions countdown or starting restriction message and arrange repair promptly.
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.