OBD-II code · Network
U0165 Lost Communication with Auxiliary HVAC Control Module
The Auxiliary HVAC Control Module has stopped transmitting on the vehicle data bus, so other control units no longer receive its messages. Rear or auxiliary climate control stops working. Typical causes are loss of power or ground at the module, an open or shorted CAN/LIN bus wire, a connector fault, or an internal module failure.
Is it safe to drive with U0165?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyAuxiliary HVAC module unpowered
- PossibleCAN wiring to auxiliary HVAC broken
- Less likelyGateway module routing CAN messages incorrectly
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Best left to a mechanic
- Typical labour
- 1–4 h
- Emissions test
- Usually unaffected
- Parts involved
- HVAC Control Module, Can Bus Wiring
Related codes
- U0162Lost Communication with Navigation Display Module
- U0163Lost Communication with Navigation Control Module
- U0164Lost Communication with HVAC Control Module
- U0166Lost Communication with Auxiliary Heater Control Module
- U0167Lost Communication with Vehicle Immobiliser Control Module
- U0168Lost Communication with Vehicle Immobilizer Control Module
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.