P23ADNOx Sensor Circuit Range/Performance (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
- P23AD flags the third NOx sensor on bank 1 as electrically intact but not trustworthy. GM's 2025 diesel table 25OBDG04B describes the check for its post-second-catalyst NOx sensor: the internal stability flags of the NOx and lambda current control are watched, and a flag counts as off when, for instance, the V2 cell voltage leaves a 40 mV band around its set point or the pump currents Ip1 and Ip2 change faster than allowed. If the off share exceeds 0.50 %, with fuel request and its rate steady, dew point passed and the heater on target, the fault matures after 2 of 2 samples; Type B, MIL after two trips. CARB demands monitoring of NOx sensor performance. P23AE and P23AF are hard out-of-range values, P2201 the front sensor.
- What you may notice
- Check engine light after two trips
- Sensor 3 NOx value jumps in live data
- SCR efficiency monitor may not complete
- Likely causes
- LikelyAged or poisoned sensing cell giving unstable pump currents
- PossibleHigh contact resistance in the sensor 3 wiring
- RareExhaust leak near the sensor upsetting the measurement
- 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.