U0165 code meaning
Lost Communication With HVAC Control Module - Rear
What U0165 means
U0165 names a second climate unit, the rear HVAC control module, fitted in vans, minivans and large SUVs that heat and cool the back rows with their own blower and flaps. The code says this rear module has gone quiet on the network; the front unit is covered by U0164. No manufacturer documents U0165 publicly, and the GM/Saab and Ford code lists checked here skip it. The trigger follows the pattern GM gives for every code from U0100 to U02FF: the module's periodic availability message fails to arrive while the supply lies between 9 and 16 V, and each listener records the fault. Rear vents then stop reacting or keep a fixed setting, while the front climate and the engine run normally. No MIL is expected.
U0165 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.3 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0165
- Rear climate controls without function
- Rear blower stuck off or at one speed
- Front climate keeps working normally
Common causes of U0165
- Most likelyRear HVAC module without power or ground (fuse, connector)
- PossibleBus wiring to the rear unit chafed under trim or at sliding-door area
- Less likelyVehicle coded for rear climate that is not fitted
- Less likelyRear HVAC control module faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Hvac control moduleCAN bus wiring
What each part of U0165 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 65 | The exact fault in that area. |
What to do next
- Note U0165 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U0165
What does U0165 mean?
U0165 means "Lost Communication With HVAC Control Module - Rear". U0165 names a second climate unit, the rear HVAC control module, fitted in vans, minivans and large SUVs that heat and cool the back rows with their own blower and flaps. It is a generic code, so it means the same on every make.
Is it safe to drive with U0165?
U0165 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will U0165 fail an emissions test?
U0165 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is U0165 to fix?
Difficulty: medium. A typical repair takes 0.3 to 3 hours of work. This is a job for a workshop.
Will U0165 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.