P22FC: NOx Sensor Performance - Slow Response Low to High (Bank 1 Sensor 2)

What it means

NOx sensor on bank 1 sensor 2 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 2 is the downstream NOx sensor after the SCR catalyst on bank 1. The module monitors how quickly this sensor reports rising NOx and sets this code when the low-to-high response is too slow. A delayed downstream reading can make it harder to assess SCR catalyst performance and emissions.

Common causes

Most likely first.

1. Sensor aged
2. Sensor element aged beyond calibration window
3. 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

1. Save freeze-frame data and review both NOx sensor readings to see whether the slow rise was recorded downstream of the SCR catalyst.
2. Use service information to identify bank 1 sensor 2 and inspect its connector and wiring for corrosion, loose pins, or heat damage.
3. Check the downstream sensor and nearby exhaust for soot deposits, damage, or leaks that could affect the reading.
4. Compare bank 1 sensor 2 response with upstream NOx data and reductant dosing commands on a scan tool.
5. If the wiring and exhaust checks pass, test the downstream sensor's rise response using the manufacturer's procedure.

Common fixes

• Repair damaged wiring or poor connections at bank 1 sensor 2.
• Repair an exhaust leak affecting the downstream NOx measurement, if present.
• Replace bank 1 sensor 2 if it fails the response test.
• Correct an identified source of oil, soot, or coolant contamination.

Can I keep driving?

You can generally drive gently if the vehicle runs normally, but emissions monitoring may be unreliable. Address AdBlue/DEF alerts promptly, since a restart countdown on some vehicles can eventually prevent restarting.