Powertrain, generic (extended)

P22F9 NOx Sensor Performance - Slow Response Low to High (Bank 1 Sensor 1)

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

Likely causes

Front NOx sensor aged or contaminated (oil ash, silicone, cleaning agents), reacting slowly
ECM calibration error, fixed by reprogramming (GM 24-NA-058 for the 2024 L5P)
Exhaust leak ahead of the sensor diluting the gas sample
Soot or deposits covering the protective cap of the sensor

Symptoms

  • Check engine light on after two drives
  • Usually no noticeable change in driving
  • SCR efficiency codes may follow

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€0–1,100
Time0.3–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

nox sensor

Related codes

P22FAP22FBP22FCP2201P2200

References: gsi.ext.gm.com, gsi.ext.gm.com, static.nhtsa.gov, law.cornell.edu.