P23B3NOx Sensor Heater Control Circuit High (Bank 1 Sensor 3)
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- If, on NOx sensor 3 of bank 1, the heater control pin sits at supply voltage when the electronics expect it to switch, P23B3 is stored. GM's 2025 diesel table 25OBDG04B describes it, for the sensor behind the second catalyst, as a battery short at the heater drive pin, evaluated every 25 ms with sensor supply above 9.9 V and dew point reached, and failing at 80 of 160 samples; Type B with the MIL on the second trip. GM also lists P23B3 in bulletin 21-NA-149 for 3.0L LM2 Duramax light trucks of 2021–2022. CARB requires the OBD system to catch heater circuit states that contradict the command, naming a short to 12 V as the example. As electronics and heater form one unit, the complete sensor is usually replaced once the harness is ruled out. P23B2 is the ground short.
- What you may notice
- Check engine light after two trips
- Sensor 3 heater status shows an error in live data
- SCR warning
- Likely causes
- LikelyHeater control wire shorted to a supply line
- PossibleHeater driver inside the sensor 3 electronics failed
- RareHeat-damaged connector with pins touching
- 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.