U0166Lost Communication With Auxiliary Heater Control Module
- Generic OBD-II code · Network
- How the car detects it
- U0166 reports that the auxiliary heater control module has stopped communicating. Such heaters, burning fuel or working electrically, warm the coolant or the cabin air before or during a drive and are common on diesels and cold-climate packages. GM lists the code in the engine controller of the 6.6 L LML Duramax (14OBDG10): it fails when no message from the heater module has come in for more than 2.5 s after the ignition has been on for at least 3 s at 9-16 V, and it is a special Type C fault that does not light the MIL. The Saab 9-5 U-code list and Ford's 2014 Boss 302S code list also include U0166. U0164 is the main HVAC module. In practice the extra heater stays off, so warm-up and cabin heat take longer in winter.
- What you may notice
- Auxiliary or parking heater does not start
- Slow engine and cabin warm-up in cold weather
- Code stored in the engine or climate controller
- Likely causes
- LikelyHeater module fuse blown or ground corroded (often underbody mounting)
- PossibleCorroded heater connector from road splash
- PossibleBus line to the heater damaged
- RareAuxiliary heater control unit faulty
- Repair
- Medium · Usually a job for a workshop.Typical cost: €40 – €1,200
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.