P23BDNOx Sensor Performance - Signal Biased/Stuck High (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
- P23BD means NOx sensor 3 on bank 1, the last probe downstream of the second SCR catalyst, reports more NOx than the operating state allows, or its value no longer comes down from a high level. A common test is engine overrun without fuel, when the exhaust contains no NOx at all: Volvo, for its inlet-sensor counterpart P225C, expects the reading to fall below 50 ppm within roughly 10 s. Ford's 2023 diesel summary allows the front sensor a positive offset of about 40 ppm under P2201. No manufacturer publishes P23BD itself. CARB names the offset-high failure mode for NOx sensors explicitly. A falsely high value behind the SCR system can make a healthy catalyst look worn out and lead to needless parts. P225C and P225E are sensors 1 and 2.
- What you may notice
- Check engine light on
- SCR efficiency code may follow although the catalyst is fine
- Sensor 3 reading stays high in overrun
- Likely causes
- LikelyMeasuring cell drifted upward with age or contamination
- PossibleSensor element damaged by thermal shock or poisoning
- RareMonitor calibration too strict, fixed by an engine software update
- 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: €150 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.