P20E6
Reductant Injection Air Pressure Too Low
The DEF system air-assist pressure is below the required threshold — pump weak, line leak, or pressure-control valve stuck open.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
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
Ordered by how often each turns out to be the cause.
- Air pump weakCommon
- Leak in air linePossible
Parts involved
- Reductant Air Pump
- Reductant Air Pressure Control Valve
- Reductant Air Line
P20E6 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.