P23C1NOx Sensor Performance - Sensing Element (Bank 1 Sensor 3)
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- P23C1 asks whether the measuring cells of NOx sensor 3 on bank 1 have lost sensitivity, for example because deposits clog the internal cavities. GM's 2025 table 25OBDG04B runs the test on the post-second-catalyst sensor during afterrun: the sensor shifts its internal pump currents so that oxygen in the second cavity rises to a target, and the outcome is set against a value the supplier recorded on the new part and wrote into the sensor EEPROM. A ratio above 125 % or below 75 % fails; results are smoothed with EWMA logic, the check runs once per trip at engine speeds under 1,500 rpm and exhaust temperatures below 400 °C, with Type A rating and a one-trip MIL. GM bulletin 21-NA-149 also lists P23C1 on 3.0L LM2 trucks. P22FB and P22FE are sensors 1 and 2.
- What you may notice
- Check engine light after one trip
- SCR monitoring results become unreliable
- No noticeable change in engine behaviour
- Likely causes
- LikelyInternal measuring cavities clogged by ash or other deposits
- PossibleSensing cells worn out after high mileage
- RareWiring fault upsetting the sensor supply during the test (GM 3.0L LM2)
- 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 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.