P2ADC: Reductant Tank Temperature Sensor B Circuit High

P2ADC is the upper limit check on the same sensor B: the reported DEF temperature is higher than the fluid in the tank could ever get. In GM's 2017 and 2018 diesel calibrations the quality sensor thermistor has to exceed 155 °C in 40 of 50 samples, with cranking finished and more than 11 V at the powertrain relay; the outcome is a Type A code. GM's 2025 DEF controller draws the line much lower at 90 °C, held for 2 s and again computed inside the smart tank unit. GM bulletin 21-NA-149 names P2ADC among the codes that a chafed engine harness produced on 2021 trucks and SUVs with the 3.0 L LM2 diesel. Such a high value usually means trouble in the sensor electronics or its wiring rather than real heat. Too low and unsteady signals are handled by P2ADB and P2ADD.

Symptoms

• Check engine light on
• DEF system message, often together with other harness-related codes
• Possible inducement countdown toward reduced power

Most likely causes

• Internal fault in the quality sensor or smart tank sensor unit
• Chafed engine harness disturbing the sensor circuit
• Corroded or loose pins at the tank sensor connector

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. Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
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 P2ADC means

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

Frequently asked questions

Can I keep driving with code P2ADC?

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

What causes code P2ADC?

The most common causes are: internal fault in the quality sensor or smart tank sensor unit; chafed engine harness disturbing the sensor circuit; corroded or loose pins at the tank sensor connector.

Related codes

• P2ADAReductant Tank Temperature Sensor B Circuit Range/Performance
• P2ADBReductant Tank Temperature Sensor B Circuit Low
• P2ADDReductant Tank Temperature Sensor B Circuit Intermittent/Erratic
• P2ADEReductant Tank Temperature Sensor B Circuit
• P205DReductant Tank Temperature Sensor A Circuit High

Sources

• gsi.ext.gm.com: 18OBDG04 Engine Diagnostics
• gsi.ext.gm.com: 17OBDG04 Engine Diagnostics
• gsi.ext.gm.com: 25OBDG04A
• static.nhtsa.gov: MC 10205552 9999

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.