Code U0661 indicates that the HVAC control module has lost communication with the right rear temperature actuator. This actuator adjusts the temperature of the air directed to the right rear passenger area. The fault is typically due to a failed actuator, wiring issue, or poor connection.
The actuator motor or its internal electronics have failed, preventing communication with the HVAC module.
Open, short to ground, or short to power in the LIN bus or power/ground wires between the HVAC module and the actuator.
Corrosion, bent pins, or loose terminals at the actuator connector causing intermittent or no communication.
The module itself may have an internal fault that prevents it from communicating with the actuator, though this is less common.
A short to ground or power on the LIN bus circuit can disrupt communication between the module and actuator.
Rarely, a software glitch or internal fault in the powertrain control module can cause erroneous U0661 codes, but this is the least likely cause.
The most common cause is a failed right rear temperature actuator. Wiring issues or poor connections are also frequent. The HVAC control module or PCM are rarely at fault.
Yes, the vehicle is drivable. The code affects only the right rear temperature control, so overall vehicle operation is not impacted. However, comfort for rear passengers may be compromised.
Almost never. This code is specific to the HVAC system. Replacing the PCM will not fix the issue and is a common misdiagnosis. Focus on the actuator, wiring, and HVAC module.
Diagnosis involves checking the actuator and its circuit for power, ground, and communication signal integrity. A scan tool is used to command the actuator and monitor response. Visual inspection and electrical testing are key.