Powertrain, generic (extended)

P2ADB Reductant Tank Temperature Sensor B Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Defective thermistor in the DEF quality or tank sensor unit
Moisture or DEF crystals in the sensor connector
Damaged signal or supply wiring to the tank sensor

Symptoms

  • 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

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€150–1,500
Time0.5–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

reductant tank temperature sensor bwiring harnessscr module

Related codes

P2ADAP2ADCP2ADDP2ADEP205C

References: gsi.ext.gm.com, gsi.ext.gm.com, gsi.ext.gm.com, law.cornell.edu.