U0425Invalid Data Received From Auxiliary Heater Control Module
- Generic OBD-II code · Network
- How the car detects it
- U0425 concerns the auxiliary heater control module, the controller of an extra heat source such as a fuel-fired coolant heater on a diesel. The HVAC or engine controller sets it when the heater's status frames arrive with implausible content. No manufacturer documents U0425 publicly; GM's 2013 bulletin PIP5094 merely includes it in a long list of codes for which terminal fit should be checked before circuit tests. Ford's patent US 10,124,649 shows how such a heater is tied into the network: it talks to the HVAC unit over the bus and to the engine controller through a bus interface, receives ambient temperature from it and runs its own fuel pump. GM's 6.6 L Duramax ECM (2014) watches messages from this module, stating lost contact as U0166, Special Type C. U0325 is software. The heater stays off; no MIL is expected.
- What you may notice
- Auxiliary or parking heater does not start
- Slow warm-up and weak cabin heat in cold weather
- Likely causes
- PossibleAuxiliary heater control unit faulty or locked after an internal fault
- PossibleLow supply voltage at the heater, for example from a weak battery
- RareLoose terminals or corrosion in the heater's bus connector
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €50 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.