What it means
The NOx sensor on Bank 1 Sensor 3 responds too slowly when the measured level falls.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The Bank 1 Sensor 3 NOx sensor measures exhaust nitrogen oxides, and the control module checks how quickly its signal follows a fall in measured NOx. P23C0 sets when the signal takes longer than expected to move from a higher reading to a lower one, which may reflect a slow sensor or an unstable reference supply.
Common causes
Most likely first.
- Sensor element aged
- Sensor element contaminated by oil, soot or coolant
- 5V/reference voltage unstable under load
Symptoms
- Check engine light
- Possible NOx or aftertreatment warning
- Increased NOx emissions or failed emissions test
How to diagnose it
- Use a scan tool to save freeze-frame data and check Bank 1 Sensor 3 response along with any reference-supply or related sensor codes.
- Review live data through conditions where NOx readings should fall and confirm whether this sensor's high-to-low response is delayed.
- Inspect the sensor connector and harness for corrosion, damaged insulation, loose contacts, or heat exposure.
- Test reference supply stability and circuit connections under the manufacturer's specified conditions, since supply instability can affect response.
- If wiring and supply are sound, test the Bank 1 Sensor 3 NOx sensor and exhaust conditions using the manufacturer's diagnostic procedure.
Common fixes
- Repair damaged or poorly connected Bank 1 Sensor 3 wiring and connector contacts.
- Restore a stable reference supply if testing identifies a circuit fault.
- Correct an exhaust, oil, coolant, or soot issue confirmed to affect the sensor.
- Replace the Bank 1 Sensor 3 NOx sensor if its high-to-low response remains too slow and it fails the manufacturer's tests.
- Perform any manufacturer-specified calibration or relearn after repair.
Can I keep driving?
Cautious driving is generally possible if the vehicle operates normally, but delayed NOx readings can impair emissions control and lead to an aftertreatment warning or emissions test failure. Arrange diagnosis soon, especially if other exhaust warnings appear.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.