Powertrain, generic (extended)

P20A6 Reductant Injection Air Pressure Control Valve Circuit/Open

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

In an air-assisted DEF system the compressed air must reach the mixing point at a defined pressure, whether it comes from the vehicle's brake air supply or from a separate compressor. A solenoid valve sets or switches this air pressure. P20A6 marks an open circuit in its control: the controller commands the valve, but no current flows, so the atomizing air cannot be regulated. No manufacturer documents P20A6 publicly. Deutz, whose EMR L1 controller drives a similar air supply valve, files the open circuit under P2059 for the air pump or supply valve and under its own code P1062 for the air switching valve. Low and high faults of the same circuit are P20A8 and P20A9. Air-assisted dosing appeared with Bosch's Denoxtronic 1 in 2004 and was later replaced by airless systems.

Likely causes

Solenoid coil of the air pressure control valve open
Connector unplugged or wire broken near the valve
Fuse or supply feed for the valve missing

Symptoms

  • SCR warning lamp or MIL on
  • Dosing stops for lack of atomizing air
  • Power derate on heavy vehicles

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–500
Time0.5–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

reductant air pressure control valve

Related codes

P20A7P20A8P20A9P2059

References: law.cornell.edu, serdia.deutz.com, energy.gov.