P21C5Reductant Level Sensor A Stuck
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- P21C5 is a plausibility code: the level sensor A reports valid readings, yet they hardly move when the fluid in the tank should be sloshing. GM spells this out for the ultrasonic sensor in its 2025 diesel tables, where it is sensor 1. While the vehicle is above 5 km/h, accelerating by more than 0.1 m/s², the fluid is liquid and over 5 L remain, a level change below 0.3 mm within one second counts as a failed sample; after about 200 s of such samples the module sets the code as Type B, so the MIL comes on after two trips. Jaguar issued SSM73632 for the 2017 to 2018 F-Pace with P21C5-64 and blamed a level sensor calibration, fixed by new engine software. Electrical faults of the same sensor are P203A to P203E, sensor B stuck is P21C6.
- What you may notice
- Check engine light on after two drives
- DEF gauge stays at the same value while fluid is being used
- DEF warning messages in the instrument cluster
- Likely causes
- LikelyLevel sensor calibration in the engine software (update available, e.g. Jaguar)
- PossibleUltrasonic level sensor in the tank unit faulty
- PossibleCrystal deposits or gas bubbles disturbing the echo
- RareFluid partly frozen or slush around the sensor
- 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 – €1,200
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.