U066BLost Communication With Turbocharger/Supercharger Bypass Valve B Position Sensor
- Generic OBD-II code · Network
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- When the throttle snaps shut, a compressor bypass valve lets boosted air recirculate to the inlet side instead of surging against the closed plate. Engines with two chargers or two compressor stages can carry a second such valve, and if its electric actuator reports the opening angle as a digital message, U066B means the engine controller no longer gets valid position frames from valve B. No manufacturer documents this code publicly. Ford's 2024 gasoline summary checks bypass valve B only for circuit faults (P00C1/P00C2 after 5 s) and lists no position feedback for it. Analog position faults on valve B would be P2C2A to P2C2C; valve A has U0657. CARB demands a separate code for lost communication of digital inputs. Boost is usually limited.
- What you may notice
- Check engine light
- Boost limited, reduced power
- Compressor surge noise when lifting off the throttle
- Likely causes
- LikelySignal, supply or ground wire to the bypass valve B actuator damaged
- PossibleConnector at the valve loose, corroded or heat-damaged near the turbo
- PossiblePosition sensor electronics in the valve actuator failed
- RareEngine controller input or software fault
- 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 – €700
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.