P23C1 code meaning
NOx Sensor Performance - Sensing Element (Bank 1 Sensor 3)
Powertrain system Generic code P23xx codes Check engine light
What P23C1 means
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.
P23C1 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 P23C1
- Check engine light after one trip
- SCR monitoring results become unreliable
- No noticeable change in engine behaviour
Common causes of P23C1
- Most likelyInternal measuring cavities clogged by ash or other deposits
- PossibleSensing cells worn out after high mileage
- Less likelyWiring fault upsetting the sensor supply during the test (GM 3.0L LM2)
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 P23C1 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. |
| C1 | The exact fault in that area. |
What to do next
- Note P23C1 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 P23C1
What does P23C1 mean?
P23C1 means "NOx Sensor Performance - Sensing Element (Bank 1 Sensor 3)". P23C1 asks whether the measuring cells of NOx sensor 3 on bank 1 have lost sensitivity, for example because deposits clog the internal cavities. It is a generic code, so it means the same on every make.
Is it safe to drive with P23C1?
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 P23C1 fail an emissions test?
Yes, it can. P23C1 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 P23C1 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 P23C1 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.