Corroded, loose or damaged connector at the reductant pump or supply module; Open circuit, high resistance or chafed wiring in the pump supply feed; Blown fuse or faulty relay supplying the pump; Failing reductant pump drawing excessive current and pulling the supply voltage down; Weak battery, poor battery terminals or charging system fault causing low system voltage; Poor earth connection on the pump or control unit circuit; Internal fault in the reductant control unit or its driver circuit.

P05EF

Reductant Pump Supply Voltage Circuit Low.

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
EF: FaultThe specific fault in that area

What it means

P05EF means the control unit that manages the selective catalytic reduction (SCR) reductant system, which doses urea-based exhaust fluid, detected a low voltage on the supply circuit feeding the reductant pump. The voltage at the pump supply was below the expected range when the pump was commanded or powered. This points to a fault in the supply wiring, fuse, relay, connector or the pump itself, or to a low system voltage. The exact circuit layout and pump location depend on the vehicle and engine.

Symptoms

Warning light on the dashboard, often with an exhaust fluid or emissions system message
Reduced engine power or limp mode on some vehicles
Countdown to a restricted engine restart or no-start warning on some models
Reductant not being injected, leading to higher NOx emissions
Possible failed emissions test
Related reductant dosing or pressure codes stored alongside

Possible causes

Corroded, loose or damaged connector at the reductant pump or supply modulelikely
Open circuit, high resistance or chafed wiring in the pump supply feedlikely
Blown fuse or faulty relay supplying the pumplikely
Failing reductant pump drawing excessive current and pulling the supply voltage downpossible
Weak battery, poor battery terminals or charging system fault causing low system voltagepossible
Poor earth connection on the pump or control unit circuitpossible
Internal fault in the reductant control unit or its driver circuitrare

How to diagnose

Read all stored codes and freeze frame data, noting battery voltage, engine state and whether other reductant or voltage codes are present
Check battery condition and charging voltage, and clean and tighten battery terminals and main earths
Check the fuse and relay for the reductant pump circuit using the vehicle wiring diagram
Inspect the pump connector, wiring and any heater circuit connections for corrosion, water ingress, pin damage and chafing
Measure the supply voltage at the pump connector with the circuit active, ideally under load, and compare with battery voltage
Voltage-drop test the supply and earth paths to find any high resistance
Check the pump current draw and operation using a scan tool active test if the vehicle supports it
Check the manufacturer's service information for known faults or updates for the model and engine

How to fix

Clean, repair or replace corroded or damaged connectors and terminals
Repair or replace damaged wiring in the pump supply or earth circuit
Replace a blown fuse only after finding why it failed, and replace a faulty relay
Replace the reductant pump or supply module if it draws excess current or fails testing
Restore battery and charging system health by replacing the battery or repairing the charging fault
Repair or replace the control unit only after the wiring and pump are proven good, following the manufacturer's procedure

Can I keep driving?

Medium severity

The car can usually be driven for a short time, but the emissions system is not working properly and some vehicles will go into reduced power or restrict restarts after a countdown. Get it checked soon so you are not left unable to restart.

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