U0657Lost Communication With Turbocharger/Supercharger Bypass Valve A Position Sensor
- Generic OBD-II code · Network
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- The bypass valve meant here sits on the intake side: on turbocharged petrol engines it lets compressed air recirculate when the throttle shuts, and on supercharged engines it routes air around the blower at light load. When the valve is electrically driven and reports its position digitally, U0657 marks that the position data from valve A has stopped arriving. No manufacturer publishes a description of U0657, so the exact valve and its protocol come from the vehicle's own service information. Analog circuit faults of the same sensor are P2BBB to P2BBD and an adaptation problem is P2BBE; valve B has U066B. Without position feedback the controller cannot tell whether surplus air is being released, so it may restrict boost to protect the compressor.
- What you may notice
- MIL on
- Less boost or hesitant throttle response
- Unusual whoosh or flutter when lifting off
- Likely causes
- LikelyWiring to the bypass valve open, shorted or chafed
- PossibleLoose or corroded valve connector
- PossiblePosition sensor in the valve failed
- RareEngine controller input 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 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.