P204B: Reductant Pressure Sensor Circuit Range/Performance
Standardized SAE J2012 code · P20xx — Fuel & air metering and auxiliary emission controls
What does P204B mean?
DEF pressure sensor reads within electrical range but plausibility fails — does not rise during prime, drift over a drive cycle, or stuck at a constant value.
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 Sensor drift or stuck reading
- Medium Pump pressure builds slowly
- Low Sensor element aged beyond calibration window
Likelihood is a general estimate across vehicles; your make and model may differ.
Add your car to see reports of P204B on the same make and model first.
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