P225FNOx Sensor Performance - Signal Biased/Stuck 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
- P225F is set when the downstream NOx sensor of bank 1 reports less NOx than expected or does not move away from a low value. A sensor behind the SCR catalyst that reads too low makes the catalyst look better than it is, so the efficiency monitor can no longer be trusted. The only public manufacturer source is the Volvo and Mack NOx sensor replacement guide for US10 and newer trucks: it lists P225F next to P225D among codes whose description mentions the NOx sensor although the sensor is rarely the cause, notes that the probe is reading fresh air, and tells technicians not to replace it. Leaks in the exhaust ahead of the sensor and harness faults are the more likely culprits. P225D is the upstream case; P225E the high-reading counterpart.
- What you may notice
- MIL on
- SCR efficiency cannot be confirmed, readiness may stay open
- Likely causes
- LikelyExhaust leak upstream of the downstream sensor drawing in outside air
- PossibleChafed or corroded wiring between sensor module and probe
- RareDownstream NOx sensor with reduced sensitivity
- 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: €80 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.