P209AReductant Injection Air Pressure Sensor B Circuit
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- Air-assisted DEF dosing, as in Bosch's first Denoxtronic generation of 2004, mixes the fluid with compressed air before it reaches the exhaust, and a pressure sensor confirms that this air is there. A second sensor B can sit in another air branch or serve as a cross-check for sensor A. P209A is the general circuit fault of sensor B, set when its signal or supply cannot be evaluated at all; P209C and P209D split off the clearly low and high readings. No manufacturer documents P209A publicly, and Deutz, whose air-assisted EMR L1 system has only one such sensor, uses the P2037 family for it. CARB counts air-assisted injection among the delivery functions that must be monitored. Without a usable reading the controller usually suspends dosing, NOx rises and a derate may follow.
- What you may notice
- Malfunction indicator lamp or SCR warning on
- DEF dosing suspended, higher NOx output
- Engine power derate or inducement countdown on trucks
- Likely causes
- LikelyCorroded or loose connector at sensor B, often from DEF residue or road spray
- PossibleReference voltage or ground of the sensor interrupted or out of range
- PossibleInternal electronic failure of pressure sensor B
- RareInput stage in the dosing control unit defective
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €60 – €450
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.