A failed rear mode actuator motor or its internal position sensor, which stops responding on the network.; Damaged or corroded wiring and connectors between the actuator and the module it communicates with.; A blown fuse or poor ground that removes power from the actuator, causing it to drop off the bus.; A faulty rear HVAC control module or body control module that is not sending or receiving messages correctly.; A shorted or open controller area network (CAN) bus wire on the segment that serves the rear actuator.; Water intrusion or physical damage to the actuator or its harness, common in rear quarter panel locations.; A software glitch in the module that requires a reflash or calibration update to restore communication.

DTC codes / U06xx · Network communication / U0663

U0663Lost Communication With Rear Mode Actuator

Q: What does code U0663 mean?

Lost Communication With Rear Mode Actuator. U0663 is a generic network communication code indicating that a control module on the vehicle's data bus has lost contact with the rear mode actuator, which is the motor that directs air flow to the rear vents in vehicles with rear climate control. The module that monitors this actuator, typically the rear HVAC control module or the body control module, has stopped receiving the expected controller area network (CAN) messages from the actuator for a calibrated amount of time.

U0663 is a generic network communication code indicating that a control module on the vehicle's data bus has lost contact with the rear mode actuator, which is the motor that directs air flow to the rear vents in vehicles with rear climate control. The module that monitors this actuator, typically the rear HVAC control module or the body control module, has stopped receiving the expected controller area network (CAN) messages from the actuator for a calibrated amount of time.

SystemNetwork

Code typeGeneric (all makes)

SeverityLow

Fix difficultyIntermediate

AreaNetwork communication

Symptoms you may notice

The climate control head may show a communication fault or simply fail to change rear air flow modes.
Rear passengers may notice that air only comes out of one set of vents regardless of the mode selected.
The rear blower may run but the mode doors do not move, leaving the rear cabin too warm or too cold.
A warning light or message on the dash indicating a network or climate control fault.
Often no symptoms besides the warning light, because the rear mode actuator may default to a safe position.
In some vehicles, the front climate control may also behave erratically if the actuator shares a bus segment.

Common causes, most likely first

A failed rear mode actuator motor or its internal position sensor, which stops responding on the network.
Damaged or corroded wiring and connectors between the actuator and the module it communicates with.
A blown fuse or poor ground that removes power from the actuator, causing it to drop off the bus.
A faulty rear HVAC control module or body control module that is not sending or receiving messages correctly.
A shorted or open controller area network (CAN) bus wire on the segment that serves the rear actuator.
Water intrusion or physical damage to the actuator or its harness, common in rear quarter panel locations.
A software glitch in the module that requires a reflash or calibration update to restore communication.

How to diagnose and fix it

Connect a scan tool and read all modules for communication codes to confirm U0663 is current and not history.
Inspect the rear mode actuator connector and harness for corrosion, loose pins, or chafed wires, and repair as needed.
Check the fuse and ground for the rear HVAC circuit with a multimeter before condemning any component.
Perform a bidirectional actuator test with the scan tool to command the rear mode door and listen for motor movement.
Measure resistance and voltage on the CAN bus wires at the actuator to verify the network is intact and not shorted.
If the actuator does not respond to commands and wiring is good, replace the rear mode actuator and perform a calibration.
If communication is still lost after actuator replacement, diagnose the rear HVAC control module or body control module for internal faults.

Before you replace the rear mode actuator

A rear mode actuator that has lost communication often defaults to a defrost or floor position, so drivers may think the climate control is working when only one mode is stuck.
The code can be set by a completely dead battery or a voltage drop during cranking, so always check for a history code and clear it before chasing wiring.
Many technicians replace the actuator only to find the real fault is a corroded connector behind a rear trim panel where water leaks have gone unnoticed.
On some vehicles the rear mode actuator shares a LIN bus with other rear components, so a single failed actuator can take down communication for the whole rear climate system.
A scan tool that can read live actuator position data is far more useful than a code reader, because it shows whether the actuator is truly offline or just out of calibration.

Can I keep driving with U0663?

You can usually continue driving safely because the rear mode actuator only affects rear cabin comfort and does not impact engine, steering, or braking. Avoid long trips with rear passengers in extreme temperatures until the fault is repaired, and do not ignore repeated warning lights if other network codes appear.

Tools that help

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