Powertrain, generic (extended)

P20A9 Reductant Injection Air Pressure Control Valve Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

If the control line of the air pressure control valve shows battery voltage or excessive current where it should not, P20A9 is stored. A wire touching a positive feed, a coil with shorted turns or a bridged connector can cause it. On a low-side driven valve the coil would then be live permanently; on a high-side driver the output often detects overcurrent and shuts down. Either way the atomizing air no longer follows the commands. P20A8 is the matching short to ground and P20A6 the open circuit. No manufacturer publishes P20A9. Deutz handles the comparable faults on its air pump or supply valve as P2061 for a short to battery and P2059-19 for critically high output current. Because the air supply is shared, check for further codes on the air pressure sensors before replacing parts.

Likely causes

Coil with shorted turns causing overcurrent
Control wire shorted to a positive feed in the harness
Output stage in the dosing control unit defective

Symptoms

  • Warning lamp on
  • Air pressure uncontrolled, often too high or permanently on
  • DEF dosing suspended

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

P20A6P20A8P20AAP2061

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