What it means
NOx sensors 1 and 2 on bank 2 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 2 has two NOx sensors that provide readings used to assess nitrogen oxides across the emissions system. This code sets when the bank 2 sensor readings disagree beyond their allowed correlation over a drive cycle, which may reflect sensor drift or a real change caused by an exhaust leak or SCR problem.
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 2 under the conditions that set the code.
- Inspect both bank 2 sensor connectors and harnesses for loose or corroded terminals, heat damage, and chafing.
- Check the bank 2 exhaust around both sensors for leaks that could alter the measured NOx levels.
- Review related SCR and DEF faults and watch how both bank 2 readings change as the system warms and operates.
- If the exhaust, wiring, and SCR operation check out, test each bank 2 NOx sensor using the manufacturer's procedure to find a drifting sensor.
Common fixes
- Repair a leak in the bank 2 exhaust near either NOx sensor.
- Clean or repair a poor connection at the affected bank 2 sensor connector.
- Repair damaged wiring to the bank 2 NOx sensors.
- Replace the bank 2 NOx sensor that fails the specified test.
- Repair the SCR fault if testing shows it is causing abnormal bank 2 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.