U066C
Lost Communication With Exhaust Heat Exchanger Bypass Valve Actuator B
The vehicle bus reports loss of communication with smart exhaust heat exchanger bypass valve actuator B. Exhaust-heat recovery cannot be commanded; cabin/coolant warm-up may slow down.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
Common causes
Ordered by how often each turns out to be the cause.
- Bus wiring open or shortedCommon
- Module without power or groundPossible
- Module failedPossible
Parts involved
- Exhaust Heat Exchanger Bypass Actuator B
- Vehicle Bus Wiring
U066C is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.