P22FANOx Sensor Performance - Slow Response High to Low (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
- P22FA mirrors P22F9 for the falling edge: when engine-out NOx drops, mostly as the driver lifts off into overrun, the front NOx sensor on bank 1 takes too long to come down. GM's 2014 Cruze 2.0 diesel fails it when the signal needs more than 1.8 s between 30 and 60 % of its starting value at 1320 rpm or more; the 6.6L LML allows 2.3 s for a drop from 70 to 40 %. GM's 2016 diesel table uses a short timer above 4 s or a long one above 8 s, Type B. Software was often the real cause: GM PI1485 reflashed 2015 Cruze diesels that showed P22FA alongside a dashboard warning about poor DEF quality, and FCA flashed the 3.0L diesel of the 2014 ProMaster (18-018-15) and the 2020 Ram 1500 (18-008-21, 18-002-23). The MIL comes on.
- What you may notice
- Check engine light on
- Warning about poor DEF quality on some GM diesels
- Usually no change in engine behaviour
- Likely causes
- LikelyEngine software anomaly, cured by reprogramming (GM PI1485, FCA 18-018-15, 18-008-21)
- PossibleFront NOx sensor aged or contaminated, signal decays slowly
- RareExhaust leak near the sensor disturbing the measurement
- 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.