Powertrain, generic · Vehicle speed, idle control and auxiliary inputs

P05F8 Reductant Heater Control Module Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P05F8 is the function check of the DEF heater control module: its feedback does not match the command – heating current or power, temperature rise, or an internal module fault. The code is documented for Chrysler's 3.0 L EcoDiesel in the 2014 Ram 1500 and Jeep Grand Cherokee: several bulletins list it together with the heater codes P20BA, P20BE and P20C2, and the fix in each case was only reprogramming the engine module – a diagnostic that was too sensitive rather than a hardware defect. It is not on Chrysler's inducement list. Ford checks the same function under heater plausibility codes. Thresholds for P05F8 are not published. If it returns after a software update, check the heater elements in tank and lines and the module supply (P05ED).

Likely causes

Engine module software (Chrysler 3.0 L 2014: diagnostic revised by reflash)
Heater control module faulty internally
Heater element or line in tank or hose with abnormal current
Unstable module supply or ground

Symptoms

  • Check engine light on
  • Usually no driveability issue
  • DEF warning in cold weather, possible heater codes P20BA/P20BE/P20C2

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€100–900
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

reductant heater control modulereductant heatersengine control module

Related codes

P05EDP20BAP20BEP20C2P20B9

References: law.cornell.edu, static.nhtsa.gov, static.nhtsa.gov, static.nhtsa.gov.