P21B0Reductant Level Sensor C Circuit High
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P21B0 means GM's level sensor 3 (sensor C) shows an open circuit or a short to battery: either 3.56 to 4.74 V or more than 4.74 V, measured 1.5 ms after a test pulse, for over 3 s. The 6.6L LML and the 2014 Cruze both rate it Type A, lighting the MIL on the first trip. PIP4887B names P21B0 next to P203D and P21AB on 2010–2011 Duramax trucks showing Service Exhaust Fluid System; when all three high codes appear together, GM directs technicians to wiring and terminal tension first and to the DEF tank assembly only afterwards. A tank connector left unplugged after other work would produce the same set of codes, so check that before ordering parts.
- What you may notice
- Check engine light on at once
- Service Exhaust Fluid System message
- P203D and P21AB often stored as well
- Likely causes
- LikelyTank connector loose, unplugged or with spread terminals
- PossibleSensor 3 signal wire open or shorted to voltage
- PossibleLevel sensor C open inside the tank assembly
- 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 – €1,200
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.