U01B1Lost Communication With Particulate Matter Sensor B
- Generic OBD-II code · Network
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- U01B1 concerns a second particulate matter sensor in a diesel exhaust, used where a layout needs two of them. Such smart sensors carry their own control unit, which heats the element, measures soot build-up and sends the results to the engine controller over CAN. U01B1 is stored when that controller stops receiving frames from sensor B. No manufacturer documents this code publicly. For the single sensor, GM's 2025 tables (25OBDG04A) set the counterpart U02A3 after more than 10 s without its messages, Type B, which shows how the check works. CARB 1968.2 relies on the PM sensor to prove filter efficiency, so without sensor B the filter monitor for its branch cannot finish. Expect a MIL and no change in how the car drives; U04B2 applies if frames arrive with invalid content.
- What you may notice
- MIL on
- Particulate filter monitor shows as not complete
- Likely causes
- LikelyHeat-damaged or corroded harness or connector at sensor B near the exhaust
- PossibleSensor control unit without supply voltage or ground (fuse, relay)
- PossibleControl unit of PM sensor B faulty
- 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: €0 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.