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U0663 — Lost Communication Rear Mode Actuator

Generic OBD-II · all makesNetwork / communication

This diagnostic trouble code indicates a communication failure between the vehicle's control network and the rear climate control mode actuator. Consequently, the system cannot adjust the direction of airflow for rear passengers. This issue is typically electrical or related to the actuator module itself.

Symptoms

What causes it — most likely first

1. Damaged wiring harness to rear actuator

Wires leading to the rear of the vehicle often suffer from chafing, cuts, or wear over time.

2. Corroded or loose electrical connector

Moisture or vibration can cause poor contact at the actuator module plug.

3. Failed rear mode actuator motor

The internal motor or electronics within the actuator assembly may stop functioning.

4. Blown fuse in rear HVAC circuit

A power supply interruption will prevent the module from communicating on the network.

5. Faulty front HVAC control unit

The main climate control head unit may fail to send or receive signals correctly.

6. Main control module communication error

Internal network failure within the primary computer is possible but statistically rare.

How it's diagnosed

  1. Verify fuse integrity for the rear HVAC circuit
  2. Inspect wiring harness for physical damage or chafing
  3. Check connector pins for corrosion or bent terminals
  4. Measure voltage and ground at the actuator module
  5. Test communication line continuity with a multimeter
  6. Substitute actuator module to verify function

Code facts & related codes

SystemNetwork / communication
StandardizationSAE generic — identical on every make

Frequently asked

Will replacing the engine computer fix this code?

No, this code relates to the rear climate system, and replacing the engine computer will not resolve it.

Is it safe to drive with this code present?

Yes, the vehicle is drivable, but rear passenger comfort features will be limited.

Why does the code return after clearing it?

The underlying electrical fault or component failure remains unresolved.

Can moisture cause this communication error?

Yes, water intrusion into rear connectors or modules can disrupt communication signals.