P2ADB: Reductant Tank Temperature Sensor B Circuit Low

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.

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

Most 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

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the AdBlue/DEF level and quality, and do not add additives or water
2. With the connector unplugged, check whether the signal wire is making contact with ground.
3. Look for white crystals around the injector and the tank
4. Check connectors and heaters with the scanner
5. Run the dosing test available on your diagnostic tool
6. Replace parts only when the test points to that component

Good to know

• Repair difficulty: medium
• It can trigger limp mode.
• It affects emissions.

What each character of P2ADB means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• A: Hybrid or air and fuel
• DB: Specific fault in that system

Frequently asked questions

Can I keep driving with code P2ADB?

Deal with it soon. If the instrument cluster shows a countdown, the car may not restart once it reaches zero.

What causes code P2ADB?

The most common causes are: 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.

Related codes

• P2ADAReductant Tank Temperature Sensor B Circuit Range/Performance
• P2ADCReductant Tank Temperature Sensor B Circuit High
• P2ADDReductant Tank Temperature Sensor B Circuit Intermittent/Erratic
• P2ADEReductant Tank Temperature Sensor B Circuit
• P205CReductant Tank Temperature Sensor A Circuit Low

Sources

• gsi.ext.gm.com: 18OBDG04 Engine Diagnostics
• gsi.ext.gm.com: 17OBDG04 Engine Diagnostics
• gsi.ext.gm.com: 25OBDG04A
• law.cornell.edu: 13 CCR 1968.2

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.