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U0663 Lost Communication With Rear Mode Actuator

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

The rear mode actuator steers rear-seat air between upper outlets, such as console or roof vents, and the rear footwell. Hanon's US 11,305,608 shows a dome-shaped rear mode door doing exactly this between console vent and rear floor vent. GM uses the code: bulletin 23-NA-206 lists U0663-00, under GM's own name with the suffix Left, in the body control module of Cadillac, Corvette, Tahoe, Suburban and Yukon models from 2020 or 2021 on, as a history entry caused by software that sets no lamp and can be ignored unless it is current. The added word Left suggests GM may split rear distribution by side. When the link is truly lost, rear passengers get air only from the outlets that were open last, for instance warm air at the face or cold air at the feet.

Likely causes

Software timing in the body or climate module storing a false history code (GM)
Rear mode actuator failed
Harness to the rear HVAC unit or console damaged

Symptoms

  • No symptom if the code is only stored as history
  • Rear air stuck at the console or roof vents or at the floor
  • Rear mode button has no effect

Repair estimate

DifficultyHardWorkshop job
Parts and labour€0–600
Time0.2–4 h

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

Parts involved

rear mode actuatorvehicle bus wiring

Related codes

U0664U065FU065BU0164

References: static.nhtsa.gov, patents.google.com, patents.google.com.