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U0660 Lost Communication With Left Rear Temperature Actuator B

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

Temperature actuator B is the second door for the same rear left zone that A serves. Where a rear zone uses two doors, one typically sets the split between cold and heated air and the other trims the mix further downstream, like the downstream rear door in Hanon's US 11,305,608; makers do not publish which letter goes to which. U0660 means the climate master gets no answer from actuator B over its LIN line. There is no public maker document for U0660; GM's 23-NA-206 lists only the A actuator on the left rear. Because A still answers, the rear left zone usually keeps some control: temperatures can be reached but overshoot, lag or sit a few degrees off. B alone missing is a narrow fault that points to that actuator or its own branch of wiring.

Likely causes

Actuator B electronics or motor failed
Fault in the wiring branch or plug that only actuator B uses
Replacement actuator not assigned or calibrated by the scan tool

Symptoms

  • Rear left temperature drifts or overshoots the set value
  • Rear left zone reacts slowly to temperature changes

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

lr temp actuator bvehicle bus wiring

Related codes

U065FU0662U0164

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