P23B4NOx Sensor Heater Sense Circuit (Bank 1 Sensor 3)
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- Besides its drive line, the heater of a NOx sensor has a sense connection through which its resistance, and with it the element temperature, is measured. P23B4 reports a fault in that sense path for the third sensor on bank 1. GM's 2025 diesel table 25OBDG04B checks the HTemp pin of the post-second-catalyst sensor for an open circuit: 80 of 160 samples, Type A, MIL after one trip. A note in the table says that the Continental Gen 3.5 sensors debounce electrical faults internally for 1.5 s before reporting them, which lets the affected wire be pinpointed. Bulletin 21-NA-149 adds P23B4 to the harness-chafe list of LM2-powered 3.0L trucks from 2021–2022. Heater circuit monitoring is a CARB requirement. P23B5 is the plausibility check, P2208 and P22A6 the other sensors.
- What you may notice
- Check engine light after one trip
- Sensor 3 temperature status invalid
- Likely causes
- LikelyHeater sense lead broken between probe and module
- PossibleBacked-out or corroded terminal at the probe connector
- PossibleInternal break in the sensor 3 probe
- 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.