P20E8Powertrain
Powertrain · SAE
Reductant (AdBlue/DEF) System Pressure Too Low
Meaning
The reductant pressure in the SCR system is below the required value. AdBlue dosing for NOx reduction is compromised.
Common causes
- Faulty or weak reductant (AdBlue) pump
- Clogged or crystallised dosing injector or lines
- Low AdBlue level or poor-quality reductant
- Faulty reductant pressure sensor
- Clogged reductant filter
- Leaks in the reductant circuit or air in the system
Symptoms
- Check-engine light, possibly an emissions-system message
- Reduced power
- No-restart countdown
- Failed emissions check
- Possible limp mode
Severity
Moderate to high: with the SCR system inoperative the vehicle may limit performance and block restarting.
What to do
- Check the AdBlue level and quality (correct concentration)
- Read live reductant-pressure data: desired vs actual
- Inspect the pump, dosing injector and lines for crystallisation or blockage
- Test the pressure sensor and, if needed, replace a faulty pump or injector