P23BENOx Sensor Performance - Signal Biased/Stuck Low (Bank 1 Sensor 3)
- 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
- P23BE is the low-side mirror of P23BD: NOx sensor 3 on bank 1 shows less NOx than is plausible, or it stays near zero while the engine is clearly producing some. Behind a working SCR system the true value is small anyway, which makes a low-stuck sensor the more dangerous error for monitoring, because it can hide a failing catalyst. No manufacturer documents P23BE publicly. Ford's 2023 diesel summary sets a negative-offset limit of about 20 ppm for the front sensor under P2201. Volvo's troubleshooting guide treats the low-stuck counterparts P225D and P225F as a probe measuring outside air, so an exhaust leak or air entry is the likelier cause than the sensor. CARB lists gain-low failure modes for NOx sensors. P225D and P225F are sensors 1 and 2.
- What you may notice
- Check engine light on
- Sensor 3 reads near zero under load
- Possibly an audible exhaust leak at the rear section
- Likely causes
- LikelyExhaust leak or air drawn in ahead of sensor 3, diluting the gas
- PossibleMeasuring cell lost sensitivity and reads too low
- RareSensor not seated correctly so it samples too little exhaust
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €50 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.