P23B1NOx Sensor Heater Control Circuit/Open (Bank 1 Sensor 3)
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- A NOx sensor only measures once its built-in heater has brought the ceramic element up to temperature. P23B1 reports that the heater control side of the third sensor on bank 1 is open. GM's 2025 diesel calibration (table 25OBDG04B) looks for a missing load on the heater control pin of the post-second-catalyst sensor and fails after 80 of 160 samples at a 25 ms rate, with powertrain relay voltage above 11 V and the sensor bus relay switched on. GM rates it Type A, so the MIL comes on after a single trip. Bulletin 21-NA-149 includes P23B1 in its chafed-harness list for 2021–2022 3.0L LM2 trucks. CARB requires heater circuits to be checked for opens and shorts. P23B2 and P23B3 are shorts; P2205 and P22A3 cover sensors 1 and 2.
- What you may notice
- Check engine light after one trip
- Sensor 3 never reports operating temperature
- SCR warning on the display
- Likely causes
- LikelyHeater element in the sensor 3 probe burnt through
- PossibleBroken heater conductor between probe and sensor module
- RareProbe connector not fully engaged after a repair
- 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: €150 – €1,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.