Failed left rear temperature actuator motor or its internal position sensor; Damaged, corroded, or disconnected electrical connector at the actuator; Broken or shorted wiring in the harness between the actuator and its control module, often at a door hinge or trim pass-through; Blend door binding or jammed, overloading the actuator and causing it to drop off the communication bus; Failed rear HVAC control module or body control module that is not polling the actuator correctly; Low battery voltage or poor grounds causing intermittent network communication faults; Aftermarket accessories or previous repairs that disturbed the rear climate wiring

DTC codes / U06xx · Network communication / U0660

U0660Lost Communication With Left Rear Temperature Actuator B

Q: What does code U0660 mean?

Lost Communication With Left Rear Temperature Actuator B. U0660 is a generic network communication code indicating that a control module on the vehicle's data bus has lost contact with the left rear temperature actuator, which is the small motor that moves a blend door to control rear cabin air temperature. The module monitoring the actuator (typically the rear HVAC control module or body control module) sets this code when it stops receiving expected messages or feedback from that actuator over the local interconnect network or similar sub-bus.

U0660 is a generic network communication code indicating that a control module on the vehicle's data bus has lost contact with the left rear temperature actuator, which is the small motor that moves a blend door to control rear cabin air temperature. The module monitoring the actuator (typically the rear HVAC control module or body control module) sets this code when it stops receiving expected messages or feedback from that actuator over the local interconnect network or similar sub-bus.

SystemNetwork

Code typeGeneric (all makes)

SeverityLow

Fix difficultyIntermediate

AreaNetwork communication

Symptoms you may notice

Rear climate control temperature cannot be adjusted for the left rear zone, often stuck on hot or cold
A clicking, ticking, or whirring noise from the rear trim area when the temperature setting is changed
The rear HVAC panel may show a temperature setting that does not match the actual air output
Intermittent operation of the left rear temperature function, working on some drives but not others
Often no symptoms besides the warning light, especially if the rear zone is rarely used
Other rear climate functions such as mode or fan speed may also behave erratically if the actuator shares a bus with them

Common causes, most likely first

Failed left rear temperature actuator motor or its internal position sensor
Damaged, corroded, or disconnected electrical connector at the actuator
Broken or shorted wiring in the harness between the actuator and its control module, often at a door hinge or trim pass-through
Blend door binding or jammed, overloading the actuator and causing it to drop off the communication bus
Failed rear HVAC control module or body control module that is not polling the actuator correctly
Low battery voltage or poor grounds causing intermittent network communication faults
Aftermarket accessories or previous repairs that disturbed the rear climate wiring

How to diagnose and fix it

Verify battery voltage and charge the battery if low, then clear the code and retest to see if it returns
Inspect the actuator connector and wiring for corrosion, loose pins, or chafing, especially where the harness passes through moving panels
Command the left rear temperature actuator through a scan tool bidirectional test and watch for movement and feedback
Measure resistance and voltage on the actuator communication and power circuits to confirm the bus is intact
Remove the actuator and check that the blend door moves freely by hand; repair a binding door before fitting a new actuator
If wiring and door are good, replace the left rear temperature actuator and perform any required calibration or relearn procedure
If the actuator still does not communicate, diagnose the rear HVAC control module and its network connections

Before you replace the rear actuator

A binding blend door is a frequent root cause that is missed when technicians replace the actuator without checking door travel, and the new part fails the same way within weeks.
This code can be set by a completely dead actuator or by one that still moves but has lost its position feedback, so a visual check of movement alone does not prove the part is good.
Water leaks or condensation around the rear quarter trim can corrode the actuator connector and cause intermittent communication loss that only appears in damp weather.
A weak battery or poor body ground can set U0660 alongside several other U-codes, so clearing codes and checking for a pattern is smarter than replacing parts immediately.
Some vehicles require a calibration routine after actuator replacement, and skipping it can leave the rear temperature stuck at one extreme even with a healthy new part.

Can I keep driving with U0660?

This fault affects only rear cabin comfort and does not compromise engine, braking, or safety systems, so the vehicle is safe to drive. Avoid repeated temperature changes that may stress a binding door, and schedule diagnosis soon if the rear zone is needed for passenger comfort.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.