U0660 code meaning
Lost Communication With Left Rear Temperature Actuator B
What U0660 means
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air and the other trims the mix further downstream, like the downstream rear door in Hanon's US 11,305,608; makers do not publish which letter goes to which.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.
U0660 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyHard
- Typical labor1 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0660
- Rear left temperature drifts or overshoots the set value
- Rear left zone reacts slowly to temperature changes
Common causes of U0660
- Most likelyActuator B electronics or motor failed
- PossibleFault in the wiring branch or plug that only actuator B uses
- Less likelyReplacement actuator not assigned or calibrated by the scan tool
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Lr temp actuator bVehicle bus wiring
What each part of U0660 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 60 | The exact fault in that area. |
What to do next
- Note U0660 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U0660
What does U0660 mean?
U0660 means "Lost Communication With Left Rear Temperature Actuator B". Temperature actuator B is the second door for the same rear left zone that A serves. It is a generic code, so it means the same on every make.
Is it safe to drive with U0660?
U0660 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will U0660 fail an emissions test?
U0660 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is U0660 to fix?
Difficulty: hard. A typical repair takes 1 to 4 hours of work. This is a job for a workshop.
Will U0660 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.