What it means
The NOx sensor on bank 1 sensor 3 reports a value that stays at the upper end of its range despite changing engine conditions - sensor element biased or stuck high.
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 nitrogen oxides in the exhaust, and the control module checks whether its signal changes plausibly as operating conditions change. P23BD sets when the signal stays unusually high or near the upper end of its range instead of responding as expected.
Common causes
Most likely first.
- Sensor element biased high
- Sensor element aged beyond calibration window
- Sensor element contaminated by oil, soot or coolant
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 compare Bank 1 Sensor 3 NOx readings with engine and exhaust conditions and any related sensor codes.
- Check live data over changing operating conditions to confirm whether this sensor remains high while relevant conditions change.
- Inspect the sensor connector and harness for corrosion, damage, poor grounding, or wiring faults that could bias the signal.
- Check for oil, soot, or coolant contamination and for exhaust or aftertreatment problems that may affect the sensor reading.
- If wiring and exhaust conditions are sound, test the Bank 1 Sensor 3 NOx sensor using the manufacturer's diagnostic procedure.
Common fixes
- Repair poor connector contact, ground, or damaged Bank 1 Sensor 3 wiring found during checks.
- Address an identified oil, coolant, soot, or exhaust source contaminating the sensor.
- Repair an exhaust or aftertreatment fault shown by diagnosis to be affecting the reading.
- Replace the Bank 1 Sensor 3 NOx sensor if its signal remains biased high and it fails the manufacturer's tests.
- Carry out any manufacturer-specified calibration or relearn after repair.
Can I keep driving?
Cautious driving is generally possible if the vehicle runs normally, but an incorrectly high NOx reading can disrupt aftertreatment monitoring and emissions control. Have it diagnosed soon; increased emissions or an emissions test failure may result.
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.