Powertrain
Definition only
Lights the check engine lamp
P209D: Reductant Injection Air Pressure Sensor B Circuit High
Standardized SAE J2012 code · P20xx — Fuel & air metering and auxiliary emission controls
What does P209D mean?
The reductant injection air-pressure sensor B reads above its upper plausibility limit — open signal line or short to B+.
The code tells you which monitor failed, not which part is broken. Test before replacing parts.
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
- High Open signal line
- Low Connector pins corroded - high contact resistance
- Low Supply wire pinched against B+ source
Likelihood is a general estimate across vehicles; your make and model may differ.
Add your car to see reports of P209D on the same make and model first.
P209D in the community
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