P203BReductant Level Sensor A Circuit Range/Performance
- 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
- P203B means the level reading of sensor A is electrically present but cannot be trusted. GM's 6.6L LML and 2014 Cruze diesel set it after 5 s (Type B) when the three discrete level contacts report a combination that is physically impossible, e.g. a higher contact wet while a lower one is dry. Ford's 2023 diesel summary sets P203B when the ultrasonic sensor reports no valid level, flags itself faulty or gives a height above the tank, checked only above 0 °C fluid and 3 kg contents. GM's 2025 DEF controller uses the sensor's readiness bit, which drops on a weak or missing echo (Type B). Jaguar (Ingenium 2.0D) and FCA point to overfilled tanks, Mercedes (Sprinter 906, SCR unit) to wrong filling and poor contact at tank module pins 3 to 5. Hard wiring faults are P203C/P203D.
- What you may notice
- MIL, often with a DEF service message
- DEF gauge stuck, jumping or showing empty with a full tank
- Restart countdown on some models
- Likely causes
- LikelyTank overfilled, so the ultrasonic sensor gets no usable echo
- PossibleIce or urea crystals on the sensor after cold soak
- PossibleWrong or diluted fluid in the DEF tank
- PossiblePoor terminal contact at the tank module connector
- RareLevel sensor or tank unit defective
- 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.