U066CLost Communication With Exhaust Heat Exchanger Bypass Valve Actuator B
- Generic OBD-II code · Network
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- 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.
- What you may notice
- 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
- Likely causes
- LikelyActuator B electronics damaged by exhaust heat
- PossibleLIN, supply or ground wire under the vehicle damaged
- PossibleWater or salt corrosion in the actuator connector
- RareLow supply voltage during the check
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €60 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.