P209A
Reductant Injection Air Pressure Sensor B Circuit
A general electrical fault is reported on reductant injection air-pressure sensor B — the second air-assist pressure sensor on dual-bank or dual-injector DEF systems.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
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)
Common causes
Ordered by how often each turns out to be the cause.
- Sensor failedCommon
- Harness faultPossible
Parts involved
- Reductant Air Pressure Sensor
P209A is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.