U0165
Lost Communication With HVAC Control Module - Rear
Communication network (climate control)
Generic OBD-II
Low
What it means
U0165 means the vehicle has lost communication with the rear HVAC (climate) control module — the unit that runs heating and air conditioning for the rear cabin. The only effect is that rear climate control stops working or won't respond; the engine and all safety systems are unaffected. It usually comes down to a wiring or connector fault, a power/ground problem, or a failed rear HVAC module.
Low
Can I keep driving? Fully drivable — this only affects rear climate control; the engine and safety systems are unaffected.
Common symptoms
What you'll notice
- Rear heating/air conditioning not responding or unavailable
- Rear climate controls dead or erratic
- Front HVAC or cluster reports the rear HVAC module missing
- No temperature or fan control for rear passengers
Common causes
Most likely first
- Damaged or corroded connector/wiring at the rear HVAC control moduleLikely
- No power or ground to the rear HVAC module (blown fuse, bad ground)Common
- Water intrusion into the module or connectorCommon
- Internally failed rear HVAC control moduleLess often
How to diagnose & fix
Work through it in order
- Scan all modules and confirm the rear HVAC module isn't communicating.
- Check the fuse, power, and ground feeding the rear HVAC module.
- Inspect the module's connector and CAN wiring for corrosion, moisture, and damage.
- Repair the wiring or connector as needed.
- If it still won't respond, replace the rear HVAC module, then clear and re-test.
FAQ
Quick answers
Is it safe to drive with U0165?+
Yes — it only disables rear climate control. There's no impact on the engine, brakes, or safety systems; it's a comfort issue you can fix at your convenience.
Can I just clear U0165?+
It will return if the module still isn't communicating. Repair the wiring or module for it to stay clear, but there's no urgency beyond restoring rear climate control.
Related codes
Often seen with U0165
Read & clear U0165 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX