Powertrain, generic (extended)

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

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P22FC is reserved for the rear NOx sensor on bank 1, behind the SCR catalyst, when its signal climbs too slowly after NOx at that point increases. No manufacturer documents this code publicly, and the NHTSA bulletin index has no entry for it. GM, whose tables describe the front-sensor version P22F9, files the dynamic check of the rear sensor under P229F instead (2018 diesel fault bundle for the NOx2 dynamic test). CARB requires every NOx sensor to be watched for a loss of response rate before emissions pass the OBD limits (13 CCR 1968.2 (f)(5.2.2)(A)). Since a working SCR leaves little NOx downstream, a rising edge only shows during a dosing pause or a NOx burst. A slow outlet sensor can hide SCR faults; expect the MIL.

Likely causes

Rear NOx sensor aged or contaminated by urea deposits, oil ash or cleaning agents
Exhaust leak between SCR catalyst and sensor
Calibration of the test itself, check for software updates

Symptoms

  • Check engine light on
  • No change in driving behaviour

Repair estimate

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

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

Parts involved

nox sensor

Related codes

P22FDP22FEP22F9P229FP20EE

References: law.cornell.edu, gsi.ext.gm.com.