What it means
NOx sensor on bank 1 sensor 1 responds too slowly when NOx concentration rises (typically observed when SCR dosing is reduced or stopped). The sensor has aged or its protection cap is clogged.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Bank 1 sensor 1 is the upstream NOx sensor ahead of the SCR catalyst on bank 1. The emissions control module monitors how quickly this sensor reports a rise in NOx, such as when reductant dosing is reduced, and sets this code if the response is too slow. A slow upstream reading can interfere with SCR dosing control and emissions monitoring.
Common causes
Most likely first.
- Sensor aged or protection cap clogged
- Sensor element aged beyond calibration window
- Sensor element contaminated by oil, soot or coolant
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
- Read freeze-frame data and live NOx and reductant dosing values to confirm the fault occurred during a condition when NOx was expected to rise.
- Identify bank 1 sensor 1 from the vehicle service information and inspect its connector and wiring for heat damage, corrosion, or loose pins.
- Check the sensor body and protection cap for soot, deposits, or physical damage without disturbing the sensing element.
- Compare bank 1 sensor 1 response with the downstream NOx reading and commanded reductant changes using a scan tool.
- If wiring and exhaust conditions are sound, test the upstream sensor response using the manufacturer's procedure.
Common fixes
- Repair damaged wiring or poor connections at bank 1 sensor 1.
- Correct an exhaust leak or other condition that is affecting the sensor's gas exposure, if found.
- Replace bank 1 sensor 1 if its response remains slow and the circuit checks pass.
- Address oil, soot, or coolant contamination at its source if inspection identifies one.
Can I keep driving?
You can usually drive gently if the vehicle runs normally, but arrange diagnosis soon because NOx emissions may be high. Do not ignore an AdBlue/DEF warning or countdown, which can eventually restrict or prevent restarting on some vehicles.
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.