OBD-II code · Powertrain (generic, extended)
P204B Reductant Pressure Sensor Circuit Range/Performance
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.
Is it safe to drive with P204B?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelySensor drift or stuck reading
- PossiblePump pressure builds slowly
- Less likelySensor element aged beyond calibration window
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)
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Best left to a mechanic
- Typical labour
- 0.7–3 h
- Emissions test
- Likely to fail
- Parts involved
- Reductant Pressure Sensor
Related codes
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.