P2ADBReductant Tank Temperature Sensor B 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
- P2ADB flags a value from the second DEF tank temperature sensor that lies below the lowest temperature the sensor can physically report, so the controller treats it as a circuit fault and not as cold fluid. GM is the documented user. In its 2017 and 2018 diesel tables sensor B is the thermistor inside the DEF quality sensor: a reading under −55 °C in 40 of 50 samples (100 ms task) sets a Type A code, MIL on the first trip. The 2025 DEF controller (25OBDG04A) leaves the range check to the smart tank unit, which sends an error flag over SENT; below −50 °C for 2 s P2ADB is stored. Without a valid value the SCR controller loses one input for managing the tank temperature. The upper limit is P2ADC, unsteady readings are P2ADD.
- What you may notice
- Check engine light right after the fault is detected
- DEF or SCR system warning in the cluster
- Countdown to reduced power or restart lock if left unrepaired
- Likely causes
- LikelyDefective thermistor in the DEF quality or tank sensor unit
- PossibleMoisture or DEF crystals in the sensor connector
- RareDamaged signal or supply wiring to the tank 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: €150 – €1,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.