U0655Lost Communication With Diesel Intake Air Flow 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
- Some diesels carry a second intake air flow valve, labelled B; which flap gets that letter depends on the engine layout and the maker. When its angle sensor is a digital SENT unit, U0655 reports that the engine controller no longer receives usable position frames from it. No manufacturer documents this code in public. GM's 2025 diesel tables give SENT link codes only to valve A (U0654, Type A, 6.25 ms checks), and CARB requires a separate code whenever a digital input stops communicating. Analog sensor faults on the B side are P2396 to P239A, drive faults P2390 to P2395. Expect the flap to be switched off and left to its spring, with EGR control and regeneration limited and a likely MIL on emission-certified engines.
- What you may notice
- Check engine light
- Particulate filter regeneration postponed or blocked
- Little change in drivability in many cases
- Likely causes
- LikelyContaminated or loose connector at throttle unit B
- PossibleSignal, supply or ground wire to sensor B damaged
- PossibleDigital position sensor of valve B 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 · Often possible to do yourself.Typical cost: €60 – €700
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.