Powertrain, generic (extended)

P209E Reductant Injection Air Pressure Sensor A/B Correlation

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

When an air-assisted DEF system carries two air pressure sensors, the controller can compare them under conditions where both should read alike, for instance with the air supply shut and the lines vented to ambient, or at a steady dosing point. P209E is set when the two values stay apart by more than the calibrated margin even though each lies within its own electrical range. The code says nothing about which sensor is wrong; a slow drift of one, a restriction in only one branch or a leak between them all show up this way. The individual sensor faults are P2037 to P2041 for A and P209A to P209D for B. No manufacturer documents P209E publicly. CARB asks for such cross-checks wherever redundant inputs exist. The SCR system typically limits or stops dosing until the cause is found.

Likely causes

One of the two sensors drifted; compare both against a reference gauge
Restriction or crystal build-up in only one air branch
Leak in the air path between the two measuring points
Replacement sensor with a different pressure range fitted

Symptoms

  • SCR or engine warning lamp on
  • Live data shows clearly different values for sensors A and B at rest
  • Reduced or suspended DEF dosing

Repair estimate

DifficultyHardWorkshop job
Parts and labour€80–700
Time1–3 h

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

Parts involved

reductant air pressure sensorreductant air pump

Related codes

P2038P209BP2037P209A

References: law.cornell.edu, energy.gov, mediathek-bosch-automotive.com.