P225CNOx Sensor Performance - Signal Biased/Stuck High (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
- P225C says the upstream NOx sensor of bank 1 reports more NOx than is plausible. Volvo describes its test on US17+OBD19 trucks: during engine motoring with zero fuel the engine makes no NOx, so the inlet sensor must fall below 50 ppm within about 10 s; each failure lights the MIL, which needs three clean drive cycles to go out. Volvo admitted false settings and told dealers not to replace the sensor. Mack and Volvo (KC-107) demand a NOx conversion test first; inlet and outlet should agree within 40 ppm before shutdown. Isuzu cured P225C on 2021 F-Series 5.2L trucks with a DCU update. FCA found most returned sensors from 3.0 EcoDiesel Ram and Jeep models fault-free and points to intake or EGR leaks, soot-clogged sensor ports and skewed MAF or coolant readings.
- What you may notice
- MIL on, often without any noticeable driving fault
- Code returns after the NOx sensor has been replaced
- Higher DEF consumption or SCR efficiency codes in some cases
- Likely causes
- LikelyEngine or DEF control unit software that flags the sensor too eagerly
- PossibleLeak in the charge air path or an EGR valve stuck partly open
- PossibleAir mass or coolant temperature signal that skews the NOx model
- RareUpstream NOx sensor with a genuine positive offset
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €100 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.