Powertrain, generic (extended)

P209B Reductant Injection Air Pressure Sensor B Circuit Range/Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

Here the wiring of air pressure sensor B is intact and the voltage lies inside its valid band, yet the reported pressure makes no sense for the moment. Typical checks compare the value with the switching state of the air supply: pressure must rise when air is released to the mixing chamber and fall back when it is shut off, and with the system at rest it should sit near ambient. A sensor that sticks, drifts or reacts too slowly fails these tests. No manufacturer publishes P209B; Deutz reports such plausibility errors on its single air pressure sensor with its own code P1119. Besides the sensor, a leaking air line, a sticking supply valve or a clogged sensing port can produce the same picture. CARB requires rationality checks for every input the dosing strategy relies on.

Likely causes

Sensor B drifting or responding sluggishly
Leak in the atomizing air line between valve and dosing module
Sensing port blocked by urea crystals or dirt
Air supply valve sticking, so the expected pressure change does not occur

Symptoms

  • Check engine or SCR warning lamp
  • Dosing reduced or stopped, possible NOx efficiency codes later
  • No noticeable change in driving until an inducement starts

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 sensor

Related codes

P209AP209CP209DP209EP2038

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