OBD-II code · Network
U0664 Lost Communication With Rear HVAC Air Cutoff Actuator
The vehicle bus reports loss of communication with smart rear HVAC air cutoff actuator (shuts the rear duct entirely off). Cutoff cannot be commanded; rear airflow stays in last-known position.
Is it safe to drive with U0664?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyBus wiring open or shorted
- PossibleModule without power or ground
- PossibleModule failed
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
- 0.5–2 h
- Emissions test
- Usually unaffected
- After the fix
- A drive cycle is needed before the light stays off
- Parts involved
- Rear HVAC Cutoff Actuator, Vehicle Bus Wiring
Related codes
- U0661Lost Communication With Right Rear Temperature Actuator A
- U0662Lost Communication With Right Rear Temperature Actuator B
- U0663Lost Communication With Rear Mode Actuator
- U0665Lost Communication With Fuel Rail Pressure Sensor Bank 2
- U0666Lost Communication With Reductant Pressure Sensor
- U0667Lost Communication With Engine Oil Temperature Sensor A
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.