Powertrain
Definition only
Lights the check engine lamp
P209C: Reductant Injection Air Pressure Sensor B Circuit Low
Standardized SAE J2012 code · P20xx — Fuel & air metering and auxiliary emission controls
What does P209C mean?
The reductant injection air-pressure sensor B reads below its lower plausibility limit — short to ground or sensor internal short.
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 Short to ground
- Low Connector pins corroded - high contact resistance
- Low Harness chafing through insulation
Likelihood is a general estimate across vehicles; your make and model may differ.
Add your car to see reports of P209C on the same make and model first.
P209C in the community
Ask about P209CNo one has posted about P209C yet
Share your vehicle, the tool you used and what you tested — the first thread helps everyone who searches for this code.
Describe your P209C problem