P22FDNOx Sensor Performance - Slow Response High to Low (Bank 1 Sensor 2)
- 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
- P22FD stands for the falling edge at the rear NOx sensor on bank 1: after a NOx peak downstream of the SCR catalyst, the signal decays more slowly than permitted. No manufacturer documents this code publicly, and no bulletin in the NHTSA index names it. How such a check works is visible in GM's front-sensor test P22FA, which times the drop between two fractions of the starting value (on the 6.6L LML 2.3 s from 70 to 40 %), while GM itself puts rear-sensor dynamics into P229F. Engines with a third NOx sensor have P23C0 for the same fault at sensor 3. Section (f)(5.2.2)(A) of CARB's OBD II rule names response rate among the sensor faults to detect. A sluggish outlet sensor makes the SCR look weaker than it is and can lead to efficiency codes such as P20EE.
- What you may notice
- Check engine light on
- SCR efficiency code may appear as well
- Likely causes
- LikelyRear NOx sensor aged or coated, signal falls too slowly
- PossibleUrea crystals around the sensor tip after dosing faults
- RareExhaust leak close to the outlet 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: €100 – €1,100
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.