P20E6: Reductant Injection Air Pressure Too Low

What it means

The DEF system air-assist pressure is below the required threshold — pump weak, line leak, or pressure-control valve stuck open.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

In an air-assisted reductant system, an air pump and pressure-control components supply air that helps deliver DEF into the exhaust. This code sets when the monitored air pressure is below the required threshold, so the system may not atomize reductant as intended for NOx control.

Common causes

Most likely first.

1. Air pump weak
2. Leak in air line

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)

How to diagnose it

1. Read freeze-frame data and use a scan tool to compare commanded and measured reductant air pressure, if available, to confirm when the pressure falls short.
2. Inspect the air lines and fittings for splits, loose connections, damage, or signs of leakage.
3. Check the air-pump electrical connector, wiring, and supply for visible damage or a poor connection.
4. Use the scan tool’s available actuator test to check whether the air pump operates and whether pressure responds.
5. Test the pressure-control valve and pressure sensing circuit using the manufacturer’s specification and vehicle-specific service information.
6. If the air supply and its circuit test correctly, investigate a control-module fault before replacing components.

Common fixes

• Reconnect or replace a leaking or damaged reductant air line or fitting.
• Repair a damaged air-pump connector or wiring section.
• Replace a weak air pump confirmed by testing.
• Repair or replace a pressure-control valve that fails its specified test.
• Repair a confirmed pressure-sensor circuit or control-module fault.

Can I keep driving?

You can generally drive cautiously if the engine runs normally, but arrange repair soon because NOx emissions may rise and a warning or starting restriction may follow. Avoid ignoring a countdown warning; the vehicle may eventually limit or prevent restarting.