P23B8NOx Sensor Heater Sense 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
- Smart NOx sensors report heater temperature through a separate sense connection, which GM calls the HTemp pin. P23B8 means this line on sensor 3 of bank 1 is pulled to ground. GM's 2025 table 25OBDG04B looks for the ground short on the post-second-catalyst sensor once the powertrain relay is above 11 V, the relay feeding the sensor bus is switched on, the supply exceeds 9.90 V and the dew point is reached; 80 of 160 samples at 25 ms must fail, Type B with two trips. For Continental Gen 3.5 sensors GM adds that the sensor itself waits 1.5 s before passing on an electrical fault. Bulletin 21-NA-149 names P23B8 where the engine harness of 3.0L LM2 trucks has rubbed through. P23B9 is the short to power; P2210 and P22A8 cover sensors 1 and 2.
- What you may notice
- Check engine light after two trips
- Sensor 3 does not report valid NOx values
- Often stored together with other wiring-related codes
- Likely causes
- LikelySense wire chafed through and touching body, frame or exhaust ground
- PossibleWater or salt bridging the sense pin to ground in the connector
- PossibleInternal short in the sensor or its control unit
- 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: €20 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.