Network, generic

U0165 Lost Communication With HVAC Control Module - Rear

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

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.

Likely causes

Rear HVAC module without power or ground (fuse, connector)
Bus wiring to the rear unit chafed under trim or at sliding-door area
Vehicle coded for rear climate that is not fitted
Rear HVAC control module faulty

Symptoms

  • Rear climate controls without function
  • Rear blower stuck off or at one speed
  • Front climate keeps working normally

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€40–800
Time0.3–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

hvac control modulecan bus wiring

Related codes

U0164U0466U0664U010F

References: saabwisonline.com, en.wikipedia.org.