P05F6 code meaning
Exhaust Aftertreatment Power Relay Control Circuit Stuck On
Powertrain system Generic code P05xx codes Check engine light
What P05F6 means
A power relay, switched by the engine module through an output driver, feeds aftertreatment consumers such as the DEF pump, tank and line heaters and possibly NOx sensors or the SCR module. CARB requires such outputs to be checked for circuit faults and function. P05F6 is a function check on the load side: the relay stays closed although it is switched off, so the consumers keep their supply, e.g. during after-run. A patent by Delphi describes this kind of check via the voltage at the heater node. No manufacturer document available to us uses this exact code; GM and Ford monitor the same function under their own codes. If the relay fails, heaters, pump and SCR control drop out and dosing stops.
P05F6 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyEasy, DIY possible
- Typical labor0.3 to 2 hours
- Clears after repairAfter a drive cycle
Symptoms of P05F6
- Check engine light on
- DEF/AdBlue warning, possibly countdown to no-restart
- Follow-up codes for heaters, pump or NOx sensor supply
- Consumers stay powered after switch-off, battery drains
Common causes of P05F6
- Most likelyRelay contacts welded or sticking
- PossibleExternal voltage on the load side (short to positive)
- PossibleCorroded connector or relay socket
- Less likelyOutput driver in the engine module faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Aftertreatment power relayRelay control circuitEngine control module
What each part of P05F6 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 5 | Area: vehicle speed, idle control and auxiliary inputs. |
| F6 | The exact fault in that area. |
What to do next
- Note P05F6 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P05F6
What does P05F6 mean?
P05F6 means "Exhaust Aftertreatment Power Relay Control Circuit Stuck On". A power relay, switched by the engine module through an output driver, feeds aftertreatment consumers such as the DEF pump, tank and line heaters and possibly NOx sensors or the SCR module. It is a generic code, so it means the same on every make.
Is it safe to drive with P05F6?
Drive gently and only to a workshop. With P05F6 the car can go into limp mode (reduced power) to protect itself.
Will P05F6 fail an emissions test?
Yes, it can. P05F6 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P05F6 to fix?
Difficulty: easy. A typical repair takes 0.3 to 2 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P05F6 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.