P209E: Reductant Injection Air Pressure Sensor A/B Correlation
Standardized SAE J2012 code · P20xx — Fuel & air metering and auxiliary emission controls
What does P209E mean?
The two reductant injection air-pressure sensors A and B disagree by more than the allowed tolerance — one is reading off, or there is a real pressure imbalance between the two air-assist branches.
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 One sensor drifts relative to the other
- Medium Real imbalance between air branches
Likelihood is a general estimate across vehicles; your make and model may differ.
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P209E in the community
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