What it means
NOx sensors 1 and 2 on bank 1 disagree by more than the allowed tolerance over a drive cycle. One sensor drifts, or there is a real NOx gradient that exceeds the calibrated map.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Bank 1 has two NOx sensors whose readings let the emissions control system assess nitrogen oxides before and after emissions treatment. This code sets when their readings disagree beyond the allowed correlation over a drive cycle, which can point to a drifting sensor or an unexpected exhaust or SCR condition.
Common causes
Most likely first.
- One NOx sensor drifting or failing
- Damaged wiring or poor connection at a sensor
- Exhaust leak affecting sensor readings
- SCR system issue causing unexpected NOx readings
Symptoms
- Check engine light or NOx warning on
- AdBlue/DEF level or quality warning
- Possible no-start countdown after ignore period
- Failed emissions inspection (NOx)
How to diagnose it
- Record freeze-frame data and compare live readings from NOx sensor 1 and sensor 2 on bank 1 under the operating conditions that set the code.
- Inspect both bank 1 sensor connectors and harnesses for loose or corroded terminals, heat damage, or chafing.
- Check the bank 1 exhaust path around both sensors for leaks that could distort their readings.
- Review related SCR and DEF faults and compare the sensor readings as the system warms and emissions treatment operates.
- If wiring, exhaust sealing, and SCR operation check out, test each bank 1 NOx sensor against the manufacturer's procedure to identify the sensor that drifts.
Common fixes
- Repair a leak in the bank 1 exhaust near either NOx sensor.
- Clean or repair a poor connection at the affected bank 1 sensor connector.
- Repair damaged wiring to the bank 1 NOx sensors.
- Replace the bank 1 NOx sensor that fails the specified test.
- Repair the SCR fault if testing shows it is causing abnormal bank 1 NOx readings.
Can I keep driving?
A short drive may be possible if the vehicle runs normally, but arrange diagnosis soon and avoid ignoring a DEF or NOx warning. Continued incorrect emissions control can cause a failed inspection or, on vehicles that use one, a no-start countdown.
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.