Powertrain, generic (extended)

P2040 Reductant Injection Air Pressure Sensor A Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

With P2040 the injection air pressure sensor A reports a voltage above its upper limit, more than a real air pressure could produce. On Deutz's EMR L1 controller this is P2040-00 under SPN 4335, defined as a short circuit to battery. In practice that means the signal wire touches a powered conductor, the sensor ground is missing so the output floats up to the reference, or the sensor itself has failed high. A wrongly high reading is dangerous for the strategy because it could pretend that air is available when it is not, so the controller treats the signal as invalid and blocks DEF injection. Low readings are covered by P2039, implausible but in-range values by P2038. Check the ground pin first, then the harness for chafing against powered lines.

Likely causes

Signal wire shorted to battery or another powered line
Sensor ground open so the output floats high
Sensor failed with output stuck high

Symptoms

  • Emission warning lamp on
  • DEF injection blocked
  • Air pressure value shown at maximum

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

P2037P2039P2038P209D

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