P23C2NOx Sensor Delayed Response - High to Low (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
- P23C2 targets the dead time of NOx sensor 3 on bank 1 when NOx drops: the reading only starts to fall too long after the exhaust has changed, even if it then moves at a normal pace. CARB separates these two failure types in its oxygen sensor definitions, calling the time before a sensor first reacts delayed response and a sluggish transition slow response. No manufacturer documents P23C2 publicly. GM's 2025 table builds such a delay timer into the front-sensor test P22F9 for the rising edge: it runs from the moment the NOx model reaches 30 ppm until the sensor does, and more than 2 s counts as a fault. A partly blocked protective tube or aged cells are the usual reason. Sensors 1 and 2 use P24F4 and P24F5, while P23C0 stands for a slow falling transition.
- What you may notice
- Check engine light on
- Sensor 3 value holds briefly before dropping in overrun
- Engine runs normally
- Likely causes
- LikelyProtective tube partly blocked, so new exhaust gas reaches the cell late
- PossibleAged sensing cells reacting late to a change
- RareCondensate in the sensor housing after many short trips
- 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.