P23C2 code meaning
NOx Sensor Delayed Response - High to Low (Bank 1 Sensor 3)
Powertrain system Generic code P23xx codes Check engine light
What P23C2 means
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.
P23C2 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 2 hours
- Clears after repairAfter a drive cycle
Symptoms of P23C2
- Check engine light on
- Sensor 3 value holds briefly before dropping in overrun
- Engine runs normally
Common causes of P23C2
- Most likelyProtective tube partly blocked, so new exhaust gas reaches the cell late
- PossibleAged sensing cells reacting late to a change
- Less likelyCondensate in the sensor housing after many short trips
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Nox sensor b1s3
What each part of P23C2 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 3 | Area: ignition system or misfire. |
| C2 | The exact fault in that area. |
What to do next
- Note P23C2 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P23C2
What does P23C2 mean?
P23C2 means "NOx Sensor Delayed Response - High to Low (Bank 1 Sensor 3)". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P23C2?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P23C2 fail an emissions test?
Yes, it can. P23C2 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P23C2 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P23C2 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.