P22F9NOx Sensor Performance - Slow Response Low to High (Bank 1 Sensor 1)
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- P22F9 concerns the NOx sensor ahead of the SCR catalyst on bank 1 and how fast it follows a rise in engine-out NOx. After a load step the control module times the sensor signal and compares it with the curve of its own NOx model. GM's 2025 diesel table starts both timers at 30 ppm and stops them at 220 ppm; a lag beyond 2 s or a relative delay above 10 % fails the check, rated Type B with the MIL after two trips. GM's 2016 diesel table used a 50 to 200 ppm window. GM bulletin 24-NA-058 cures P22F9 on 2024 Silverado and Sierra HD with the 6.6L L5P through new ECM software. P22FA covers the falling direction, P22FC the rear sensor. A sluggish front sensor feeds the urea dosing late information, so NOx output may climb.
- What you may notice
- Check engine light on after two drives
- Usually no noticeable change in driving
- SCR efficiency codes may follow
- Likely causes
- LikelyFront NOx sensor aged or contaminated (oil ash, silicone, cleaning agents), reacting slowly
- PossibleECM calibration error, fixed by reprogramming (GM 24-NA-058 for the 2024 L5P)
- RareExhaust leak ahead of the sensor diluting the gas sample
- RareSoot or deposits covering the protective cap of the sensor
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €0 – €1,100
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.