P23B2NOx Sensor Heater Control Circuit Low (Bank 1 Sensor 3)
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- P23B2 points to the heater control line of bank 1's NOx sensor 3 being pulled to ground. GM's 2025 diesel table 25OBDG04B checks that pin on the sensor downstream of the second catalyst for a short to ground and, unlike the open-circuit test, waits until the dew point has been reached, so that the heater is actually allowed to run; 80 failed out of 160 samples set the code. GM rates it Type B, two trips before the MIL lights. The bulletin for the 3.0L LM2 diesel, 21-NA-149 (model years 2021–2022), lists the code too and traces many faults to chafed engine harnesses. CARB demands detection of heater circuit shorts that contradict what the heater was told to do. The heater can then no longer be regulated; P23B3 is the short to power.
- What you may notice
- Check engine light after two trips
- Sensor 3 slow or unable to become ready
- Likely causes
- LikelyHeater control wire chafed against ground
- PossibleInternal short in the heater of sensor 3
- RareWater bridging the heater pins in the connector
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €100 – €1,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.