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U0664 Lost Communication With Rear HVAC Air Cutoff Actuator

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

Some climate units carry a door that opens or shuts the whole air supply to the rear seats, so the system can send everything forward when nobody sits in the back or when the front needs full airflow. Hanon's US 11,305,608 places such an on-off door on the rear cold-air passage, and Denso's US 2020/0189351 moves its rear airflow door to feed or close the rear vent and heat outlets. U0664 means the climate master has lost contact with the actuator of this door. No maker documents the code in public. The impact depends on where the door stopped: closed, the rear gets no conditioned air at all; open, the rear keeps blowing even when switched off and the front loses some airflow, most noticeable during maximum cooling or defrost.

Likely causes

Rear cutoff door actuator failed
Actuator plug at the rear outlet of the HVAC case not seated
LIN or supply wire to the cutoff actuator damaged

Symptoms

  • No air at the rear outlets
  • Rear outlets keep blowing although rear climate is off
  • Reduced airflow at the front during maximum cooling or defrost

Repair estimate

DifficultyHardWorkshop job
Parts and labour€60–600
Time1–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

rear hvac cutoff actuatorvehicle bus wiring

Related codes

U0663U0164

References: patents.google.com, patents.google.com, en.wikipedia.org.