P221ANOx Sensor 1/2 Correlation (Bank 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
- P221A compares the two NOx sensors of bank 1, upstream and downstream of the SCR catalyst. When conditions should make both read alike, the gap between them is too large, so the system cannot tell which value to trust. Volvo and Mack list P221A among codes that often lead to needless sensor swaps; before replacement a NOx conversion test must show the inlet and outlet readings disagreeing by more than about 40 ppm shortly before engine shutdown, or the cause lies elsewhere. Nissan bulletin NTB16-048 covers early 2016 Titan XD trucks with the Cummins 5.0L V8: P221A with P229E and P22A7 is fixed by a new outlet sensor and ECM reprogramming. P2201 and P229F judge each sensor alone, P221B is bank 2.
- What you may notice
- Malfunction indicator lamp on
- Often stored with P20EE or other SCR codes
- Implausible NOx conversion values in live data
- Likely causes
- LikelyOne of the two NOx sensors (often the outlet sensor) reading wrongly
- PossibleExhaust leak between the two sensors diluting the reading
- PossibleECM software (Nissan Titan XD 5.0L 2016, NTB16-048)
- RareFaulty DEF dosing distorting the comparison
- 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 – €1,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.