Relay contacts welded or sticking in the closed position; Short to battery voltage in the relay control wiring; Corroded or damaged relay socket, terminals or connector; Fault in the relay driver circuit inside the control unit; Wiring harness chafed or shorted to another live circuit; Outdated or faulty control unit software affecting relay monitoring.

P05F6

Exhaust Aftertreatment Power Relay Control 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
F6: FaultThe specific fault in that area

What it means

P05F6 is a generic powertrain code meaning the control circuit for the exhaust aftertreatment power relay is stuck on. The engine control unit has commanded the relay off but still detects the circuit as energised, so the relay or its circuit is not switching as instructed. What this relay powers (for example heaters or pumps in the aftertreatment system) depends on the vehicle and engine.

Symptoms

Engine management warning light on
Possible reduced power or limp mode on some vehicles
Aftertreatment or emissions warning message on the dashboard
Battery drain after the car has been switched off
Other aftertreatment fault codes stored alongside it

Possible causes

Relay contacts welded or sticking in the closed positionlikely
Short to battery voltage in the relay control wiringpossible
Corroded or damaged relay socket, terminals or connectorpossible
Fault in the relay driver circuit inside the control unitpossible
Wiring harness chafed or shorted to another live circuitpossible
Outdated or faulty control unit software affecting relay monitoringrare

How to diagnose

Read all stored codes and freeze frame data, and note any related aftertreatment, heater or supply voltage codes.
Use the manufacturer wiring diagram to identify the relay, its fuse and the components it supplies, as this varies by model and engine.
Visually inspect the relay, socket, fuse box and connectors for heat damage, moisture, corrosion or loose terminals.
With the ignition off, check whether the relay is still clicked in or the supplied circuit is still live, which suggests stuck contacts.
Swap in a known good identical relay, if the system allows, and see if the code returns.
Check the control wire between the relay and control unit for short to voltage, and for insulation damage along the harness.
Command the relay on and off with a diagnostic scan tool and measure the control signal and output at the relay.
Check for applicable software updates for the control unit before condemning it.

How to fix

Replace a relay with welded or sticking contacts with the correct specification part.
Repair or replace shorted, chafed or damaged wiring and connectors.
Clean or replace a corroded relay socket or terminals.
Replace or repair the control unit only after wiring and relay faults are ruled out.
Update the control unit software if a known fault with relay monitoring is confirmed for that model.
Clear the code and road test to confirm it does not return.

Can I keep driving?

Medium severity

The car can usually be driven for a short time, but get it checked soon as a stuck relay may drain the battery or overheat components and may leave the aftertreatment system working incorrectly. If the car goes into limp mode or a warning message says to stop, limit driving.

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