P21AFReductant Level Sensor C Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P21AF is set when level sensor C, called level sensor 3 by GM, reads below 0.17 V right after the tank electronics apply their test pulse, which GM interprets as a short to ground. Supply must be above 8 V and the error must persist for more than 3 s. The 2014 Cruze diesel stores it as Type B, so the MIL lights after the second failing trip; on the 6.6L LML Duramax it appears in the same form, and GM bulletin 12-06-04-002C places it in the first group of DEF codes to be repaired before the warning tests can run again. When P203C or P21AA are present as well, several sensors reading low at once point to a common wiring or connector problem rather than to sensor 3 alone.
- What you may notice
- Check engine light after two trips
- DEF warning message
- Implausible DEF level shown
- Likely causes
- LikelySensor 3 signal wire shorted to ground
- PossibleWater or fluid bridging contacts in the tank connector
- PossibleLevel sensor C shorted 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: €80 – €1,200
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.