U0656Lost Communication With Turbocharger/Supercharger Boost Control A 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
- On a variable geometry turbocharger the boost control position sensor reports where the guide vanes stand, and the controller needs that feedback to regulate boost and to check, as CARB 1968.2 (f)(7.2.3) asks, that the vanes reach their target in time. GM's 2025 diesel table 25OBDG04B reads this VGT position by SENT and sets U0656 when 480 of 600 checks, run every 6.25 ms, find the protocol stuck low or high with stale data, a message error, or counters that no longer update; it is Type A with the MIL in the first trip. Low raw signal level on the same sensor is a different code there, P2564. Analog circuit faults are P2562 to P2566, charger B uses U02B0. The vanes usually go to a safe position and power drops.
- What you may notice
- MIL on
- Limp mode with clearly reduced power
- Boost control codes stored at the same time
- Likely causes
- LikelySENT, supply or ground line to the VGT actuator damaged
- PossibleConnector at the actuator exposed to heat, oil or water
- PossiblePosition sensor or electronics in the VGT 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
- Hard · Usually a job for a workshop.Typical cost: €80 – €1,200
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.