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U0661 Lost Communication With Right Rear Temperature Actuator A

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

A right rear temperature actuator is only fitted where the rear seats are split into left and right climate zones, as in four-zone systems of large sedans, SUVs and vans. Actuator A on the right is the counterpart of U065F on the left, so when this code is stored the passenger behind the front passenger seat loses temperature control while the left rear zone still works. No maker documents U0661 publicly; GM's bulletin 23-NA-206 names only the left-hand rear actuators. Hanon's US 11,305,608 shows the door arrangement that such zones rely on. Because both rear sides often share one harness and LIN segment, a single right-side code points toward the actuator itself; right and left together point toward the common wiring or the master.

Likely causes

Right rear temperature actuator A failed
Actuator plug in the right rear duct area loose or corroded
Shared rear LIN segment faulty (then usually several rear codes)

Symptoms

  • Right rear zone stays at one temperature
  • Rear right temperature buttons have no effect
  • Left rear zone continues to work normally

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

rr temp actuator avehicle bus wiring

Related codes

U0662U065FU0164

References: patents.google.com, static.nhtsa.gov, en.wikipedia.org.