What it means
The vehicle bus reports loss of communication with smart left-rear HVAC temperature blend door actuator B. Rear-left air temperature falls back to a default position.
How it works
Left rear temperature actuator B controls a separate rear HVAC blend-door function for the left rear area. U0660 sets when a control module stops receiving expected messages specifically from actuator B, so that part of left rear temperature adjustment may remain at a default position even if actuator A communicates normally.
Common causes
Most likely first.
- Bus wiring open or shorted
- Module without power or ground
- Module 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
How to diagnose it
- Scan HVAC modules for freeze-frame data and related communication faults, distinguishing actuator B's status from left rear temperature actuator A.
- Adjust the left rear temperature controls and check scan-tool data for actuator B or changes in the corresponding rear air temperature.
- Inspect actuator B's connector and harness in the left rear HVAC area for looseness, corrosion, chafing, or damage.
- Check actuator B's specified fuse, power, and ground to rule out a supply failure.
- Test actuator B's network wiring for opens, shorts, and poor connections to the manufacturer's specification before diagnosing the actuator or module.
Common fixes
- Reconnect or secure left rear temperature actuator B's connector.
- Repair damaged wiring or corroded terminals in actuator B's circuit.
- Restore actuator B's power or ground after locating the cause of the loss.
- Replace left rear temperature actuator B or its module only if testing confirms it has failed.
Can I keep driving?
Driving is generally possible if only the left rear temperature function is affected. Check that front HVAC operation and windshield clearing remain adequate.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.