P21A8Reductant Level Sensor B Circuit
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P21A8 is the general circuit code for the second reductant level sensor, needed only where a DEF tank reports its fill level through more than one sensing element. GM's 6.6L Duramax (LML/LGH) and the 2014 Cruze diesel read three discrete level sensors, numbered 1 to 3 in GM's tables, which corresponds to A to C. GM does not use P21A8 itself but splits the fault into P21AA (below 0.17 V after a test pulse) and P21AB (open load or short to battery). A maker using the umbrella code stores it for any wiring fault it cannot assign to one side. CARB requires such input circuits to be monitored (13 CCR 1968.2 (f)(15.2.1)). Expect a DEF warning message and, if left unrepaired, the usual SCR warning sequence.
- What you may notice
- Check engine light on
- DEF system warning message in the cluster
- DEF level or range display missing or wrong
- Likely causes
- LikelyDamaged or corroded harness or connector at the DEF tank
- PossibleLevel sensor B in the tank assembly failed
- RareTank level evaluation electronics 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: €80 – €1,200
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.