Powertrain, generic (extended)

P20A8 Reductant Injection Air Pressure Control Valve Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P20A8 says the air pressure control valve's drive circuit sits at too low a level, which normally means a short to ground. Depending on whether the valve is switched on the high or the low side, this either stops the valve from opening at all or energizes it without command. In both cases the controller loses control of the atomizing air. The fault differs from P20A6, where the circuit is interrupted, and from P20A9, a short toward battery voltage. No manufacturer documents P20A8 publicly. For the comparable valves of its air-assisted system, Deutz lists the high-side short to ground as P2060 on the air pump or supply valve and as P1061 on the air switching valve. CARB requires such circuit checks on every electrical component of the SCR system. A chafed harness on the frame rail is the classic finding.

Likely causes

Harness chafed through to ground along the frame
Solenoid coil shorted to the valve body
Water in the connector creating a path to ground

Symptoms

  • MIL or SCR lamp on
  • Blown fuse possible on high-side switched valves
  • Dosing stopped, derate on trucks

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–500
Time0.5–2.5 h

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

Parts involved

reductant air pressure control valve

Related codes

P20A6P20A9P20A7P2060

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