OBD-II code · Powertrain (generic)
P05F8 Reductant Heater Control Module Performance
The reductant heater module is electrically intact but does not deliver the expected thermal effect - heater elements aged, supply line resistance, or thermostat sensor offset.
Is it safe to drive with P05F8?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyHeater element aged
- Less likelyModule software outdated, reflash may resolve
- Less likelySupply voltage outside specification
Symptoms
- Check engine light or NOx warning on
- AdBlue/DEF level or quality warning
- Possible no-start countdown after ignore period
- Failed emissions inspection (NOx)
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Often, with basic tools
- Typical labour
- 0.6–2.5 h
- Emissions test
- Likely to fail
- Parts involved
- Reductant Heater Control Module
Related codes
- P05F5Exhaust Aftertreatment Power Relay Control Circuit High
- P05F6Exhaust Aftertreatment Power Relay Control Circuit Stuck On
- P05F7Exhaust Aftertreatment Power Relay Control Circuit Stuck Off
- P05F9Stop-Start Status Signal Circuit
- P05FAStop-Start Status Signal Circuit Low
- P05FBStop-Start Status Signal Circuit High
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.