What it means
The NOx sensor circuit for Bank 1 Sensor 3 has a signal that does not meet the module’s expected range or performance criteria.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Bank 1 Sensor 3 is a NOx sensor in the exhaust aftertreatment system; the control module uses its signal to assess NOx levels at that point in the exhaust. This code sets when the signal is present but its range or response does not match what the module expects, which can result from sensor drift or an exhaust leak near that sensor.
Common causes
Most likely first.
- NOx sensor bank 1 sensor 3 fault or drift
- Exhaust leak near the sensor
- Damaged wiring or poor connector contact
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 other available aftertreatment data under the recorded operating conditions.
- Inspect the Bank 1 Sensor 3 connector and harness for heat damage, corrosion, loose pins, or chafing that could distort its signal.
- Check the exhaust around Sensor 3 for leaks that could change the gas sample reaching the sensor.
- With a scan tool, monitor the Sensor 3 signal as the exhaust warms and operating conditions change to see whether it responds plausibly or remains biased.
- If wiring and exhaust are sound, test the sensor circuit and sensor response using the vehicle manufacturer's diagnostic procedure.
Common fixes
- Repair an exhaust leak near Bank 1 Sensor 3.
- Clean or repair a loose or corroded Sensor 3 connector and secure the harness away from heat and vibration.
- Repair damaged wiring affecting the Sensor 3 signal.
- Replace the Bank 1 Sensor 3 NOx sensor if its signal remains out of range after circuit and exhaust checks.
Can I keep driving?
If the vehicle runs normally, a short, gentle trip is generally possible, but arrange diagnosis soon and avoid extended driving. The fault can leave NOx emissions high and may trigger an aftertreatment warning or emissions-test failure.
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.