U066C code meaning
Lost Communication With Exhaust Heat Exchanger Bypass Valve Actuator B
Network system Generic code U06xx codes Check engine light
What U066C means
Exhaust heat recovery sends hot gas through a coolant heat exchanger after a cold start and later steers it past; the steering is done by bypass flaps. Actuator B is the second such flap, present only where the layout has two paths or stages. U066C is logged once that actuator, linked over a serial bus such as LIN, stops answering the controller. No maker has published a definition for this code. The nearest published check covers actuator A: GM's hybrid tables from 16OBDG02 on set U063E after 80 unanswered LIN requests at 40 ms (about 3.2 s), Type B with the MIL after two trips; no table lists a B actuator. CARB requires lost communication of digital parts to be detected separately. Hardware faults of flap B are P23A2 to P23A8. Expect slower warm-up in cold weather.
U066C at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U066C
- Check engine light, on some systems only after two drive cycles
- Engine and cabin heater warm up more slowly
- Hybrid engine runs longer to reach temperature
Common causes of U066C
- Most likelyActuator B electronics damaged by exhaust heat
- PossibleLIN, supply or ground wire under the vehicle damaged
- PossibleWater or salt corrosion in the actuator connector
- Less likelyLow supply voltage during the check
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Exhaust heat exchanger bypass actuator bVehicle bus wiring
What each part of U066C means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 6C | The exact fault in that area. |
What to do next
- Note U066C 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 U066C
What does U066C mean?
U066C means "Lost Communication With Exhaust Heat Exchanger Bypass Valve Actuator B". Exhaust heat recovery sends hot gas through a coolant heat exchanger after a cold start and later steers it past; the steering is done by bypass flaps. It is a generic code, so it means the same on every make.
Is it safe to drive with U066C?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will U066C fail an emissions test?
Yes, it can. U066C is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is U066C to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will U066C clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.