OBD-II code · Powertrain (generic, extended)
P209B Reductant Injection Air Pressure Sensor B Circuit Range/Performance
The reductant injection air-pressure sensor B reads inside the electrical range but does not match expected behaviour over time or load — slow response or wrong offset.
Is it safe to drive with P209B?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelySensor drift
- Less likelySensor element aged beyond calibration window
- Less likelySensor mounting loose - signal damping
Symptoms
- Check engine light or NOx warning on
- AdBlue/DEF level or quality warning
- Possible no-start countdown after ignore period
- Failed emissions inspection (NOx)
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Best left to a mechanic
- Typical labour
- 0.7–2 h
- Emissions test
- Likely to fail
- Parts involved
- Reductant Air Pressure Sensor
Related codes
- P2038Reductant Injection Air Pressure Sensor A Circuit Range/Performance
- P209AReductant Injection Air Pressure Sensor B Circuit
- P2098Post Catalyst Fuel Trim System Too Lean (Bank 2)
- P2099Post Catalyst Fuel Trim System Too Rich (Bank 2)
- P209CReductant Injection Air Pressure Sensor B Circuit Low
- P209DReductant Injection Air Pressure Sensor B Circuit High
- P209EReductant Injection Air Pressure Sensor A/B Correlation
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.