Powertrain, generic (extended)

P20A7 Reductant Injection Air Pressure Control Valve Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

With P20A7 the air pressure control valve is electrically fine, but the air pressure it should produce does not appear. The check relies on the air pressure sensor: after the valve is opened or its duty changed, the measured value must reach the target band within a set time. If pressure stays too low, overshoots or reacts sluggishly, the valve is judged ineffective. No manufacturer documents P20A7 publicly; Deutz reports comparable symptoms with its own codes, P1126 for a defective SCR air valve and P1124 for air pressure too low. Beyond a worn or dirty valve, an empty air reservoir, a leaking line or a blocked air filter upstream can explain the fault. Electrical problems belong to P20A6, P20A8 and P20A9; a valve clearly jammed in one position gives P20AA or P20AB.

Likely causes

Valve worn or contaminated with oil, water or urea deposits from the air supply
Insufficient supply pressure from the vehicle air system or compressor
Leaking air line or fitting downstream of the valve
Air pressure sensor reading wrong

Symptoms

  • SCR warning, often together with air pressure codes
  • Poor atomization, possible deposits in the exhaust pipe
  • Rising NOx and later efficiency faults

Repair estimate

DifficultyHardWorkshop job
Parts and labour€80–600
Time0.5–3 h

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

Parts involved

reductant air pressure control valve

Related codes

P20A6P20AAP20ABP2038

References: law.cornell.edu, serdia.deutz.com, mediathek-bosch-automotive.com.