What it means
The NOx sensor on Bank 1 Sensor 3 responds too slowly when the measured level rises.
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 rise in measured NOx. P23BF sets when the signal takes longer than expected to move from a lower reading to a higher 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 record freeze-frame data and check Bank 1 Sensor 3 response and any reference-supply or related sensor codes.
- Review live data through conditions that should produce changing NOx readings and confirm that the rise is unusually delayed.
- Inspect the Bank 1 Sensor 3 connector and harness for corrosion, damage, poor contact, or heat exposure.
- Check reference supply and wiring stability under the manufacturer's specified test conditions, since an unstable supply can slow the reported response.
- If supply and wiring are sound, test the sensor and exhaust conditions using the manufacturer's diagnostic procedure.
Common fixes
- Repair loose, corroded, or damaged Bank 1 Sensor 3 wiring and connector contacts.
- Repair an unstable reference supply or related circuit fault found during testing.
- Correct an exhaust, oil, coolant, or soot issue confirmed to affect the sensor.
- Replace the Bank 1 Sensor 3 NOx sensor if its low-to-high response remains too slow and it fails the manufacturer's tests.
- Perform any manufacturer-specified calibration or relearn after repair.
Can I keep driving?
The vehicle may remain drivable if it runs normally, but slow NOx response can impair emissions control and lead to an aftertreatment warning or emissions test failure. Avoid putting off diagnosis, 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.