Powertrain, generic (extended)

P2039 Reductant Injection Air Pressure Sensor A Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P2039 is stored when the signal of injection air pressure sensor A sits below the lowest voltage a working sensor can deliver. Deutz documents it on its EMR L1 controller as P2039-00 under SPN 4335 and lumps two causes together: a grounded signal and an open circuit, since the input is pulled low when the signal wire is interrupted. A loss of the 5 V reference is another common reason for a reading near zero. Because the controller can no longer confirm that atomizing air is present, it stops DEF injection; Deutz engines then run without NOx reduction until the inducement logic of the machine steps in. The opposite fault is P2040, and electrical faults of the sensor supply fall under P2037.

Likely causes

Signal wire open or shorted to ground
5 V reference to the sensor lost
Sensor output stuck low

Symptoms

  • Emission warning lamp on
  • DEF injection stopped
  • Power derate after a while on machines with inducement

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–450
Time0.5–2 h

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

Parts involved

reductant air pressure sensor

Related codes

P2037P2040P2038P209C

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