OBD-II code · Powertrain (generic)
P05F4 Exhaust Aftertreatment Power Relay Control Circuit Low
Same as P05F3 with the control line shorted to ground. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
Is it safe to drive with P05F4?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyControl line shorted to ground
- Less likelyConnector pins corroded - high contact resistance
- Less likelyHarness chafing through insulation
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Often, with basic tools
- Typical labour
- 0.5–1.8 h
- Emissions test
- Likely to fail
- Parts involved
- Aftertreatment Power Relay
Related codes
- P05F1Reductant Pump Supply Voltage Circuit Stuck On
- P05F2Reductant Pump Supply Voltage Circuit Stuck Off
- P05F3Exhaust Aftertreatment Power Relay Control Circuit Open
- P05F5Exhaust Aftertreatment Power Relay Control Circuit High
- P05F6Exhaust Aftertreatment Power Relay Control Circuit Stuck On
- P05F7Exhaust Aftertreatment Power Relay Control Circuit Stuck Off
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.