What it means
The reductant heater control module does not meet the expected performance monitor. The code does not by itself identify the heater element, supply voltage, or software as the cause.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The reductant heater control module manages electrical heating of the reductant fluid system so the fluid can be used in cold conditions. P05F8 means the module's operation did not meet its expected performance check; the code does not identify whether the module, its wiring, or another input caused the mismatch.
Common causes
Most likely first.
- Reductant heater control module fault
- Wiring or connector fault
Symptoms
- Check engine light or emissions warning may illuminate
How to diagnose it
- Record freeze-frame data and scan for related reductant heater, supply-voltage, or emissions-system codes to see when the performance check failed.
- Inspect the reductant heater control module connectors and harness for water, corrosion, loose pins, chafing, or heat damage.
- Check the module's power supply, ground, and relevant fuses under the conditions specified by the service information.
- Use scan-tool data to compare heater commands and reported module status, and check the associated circuits against the manufacturer's specification.
- If power, ground, wiring, and connected components check out, test the module according to the vehicle's service information.
Common fixes
- Clean and secure a loose or corroded module connector.
- Repair damaged wiring or a poor module ground.
- Replace a failed fuse after finding and correcting the cause.
- Replace the reductant heater control module if testing confirms an internal performance fault.
Can I keep driving?
You can generally drive cautiously if the vehicle runs normally, but the reductant system may not work as intended in cold weather and an emissions warning may remain on. Have the fault checked soon, especially if other emissions warnings or reduced-power symptoms appear.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.