Short to battery positive in the pump supply wiring, caused by chafed or damaged insulation; Faulty reductant pump or its internal driver or electronics holding the supply on; Sticking or welded relay or fuse-box switching device feeding the pump, on models that use one; Water ingress, corrosion or damaged pins in the pump or dosing system connector causing a leakage path; Fault in the SCR or engine control unit output driver; Frozen or contaminated fluid causing abnormal pump load and a false circuit reading, depending on the model.

P05F1

Reductant Pump Supply Voltage Circuit Stuck On.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
5: AreaVehicle speed, idle control and auxiliary inputs
F1: FaultThe specific fault in that area

What it means

P05F1 means the control unit has detected that the supply voltage circuit to the reductant (diesel exhaust fluid) pump is stuck on. The pump's power feed appears to stay energised when the module is commanding it off. This is part of the selective catalytic reduction (SCR) system, which cuts NOx emissions. Exact circuit layout and the module that monitors it vary by model and engine.

Symptoms

Engine management or emissions warning light on
Exhaust fluid or SCR system warning message on the dashboard
Reductant pump running or buzzing when it should be off, or the pump staying warm
Flat battery after the car has been standing, if the feed stays live
Possible reduced engine power or a restricted restart limit if the fault persists
No other obvious driveability change in the early stages

Possible causes

Short to battery positive in the pump supply wiring, caused by chafed or damaged insulationlikely
Faulty reductant pump or its internal driver or electronics holding the supply onlikely
Sticking or welded relay or fuse-box switching device feeding the pump, on models that use onepossible
Water ingress, corrosion or damaged pins in the pump or dosing system connector causing a leakage pathpossible
Fault in the SCR or engine control unit output driverrare
Frozen or contaminated fluid causing abnormal pump load and a false circuit reading, depending on the modelrare

How to diagnose

Read all stored and pending codes and the freeze frame data, noting any other SCR, NOx sensor or supply voltage codes and the conditions when the fault set.
Check the exhaust fluid level and condition, and look for crystallised deposits, leaks or damage around the tank and pump.
Inspect the pump wiring, connector and any relevant fuse and relay for heat damage, corrosion, moisture or chafing.
With the ignition off, check whether the pump feed still has voltage present using a multimeter and the manufacturer wiring diagram.
Use a scan tool's actuator tests, if supported, to command the pump on and off and watch whether the feed follows the command.
Check the harness for a short to positive by unplugging the pump and testing the circuit for unwanted voltage, then continuity and insulation.
Test the relay or switching device, if fitted, by swapping with a known good identical part or bench testing it as per the model procedure.
Check for relevant technical service bulletins or software updates for your specific model before replacing the control unit.

How to fix

Repair or replace damaged wiring and insulation that is shorting to positive, and secure the harness away from rubbing points.
Clean, dry or replace corroded or water-damaged connectors and terminals.
Replace the reductant pump or dosing module if it is confirmed to be holding the supply on.
Replace a faulty relay or switching device that is stuck on.
Replace or reprogram the control unit only after the wiring and pump have been ruled out, and only where an outdated or faulty calibration is a known cause.
Clear the code after repair and road test to confirm it does not return and the SCR system passes its self-checks.

Can I keep driving?

Medium severity

The car can usually be driven short-term, but get it checked soon because a live supply can drain the battery and a persistent SCR fault may lead to reduced power or a restart restriction. Stop driving and seek help if you smell burning or see smoke from the wiring.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.