Powertrain, generic (extended)

P209D Reductant Injection Air Pressure Sensor B Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

With P209D the second air pressure sensor reports a voltage above the top of its usable range, close to the supply or battery level. A real air pressure that high is not possible in the system, so the controller treats the value as an electrical fault. Usual explanations are a signal wire that touches a live conductor, a broken ground return so that the output floats up to the reference, or an open signal line on circuits that pull the input high. P209C is the mirror case with a reading too low, and P209A the umbrella code when the type of circuit fault cannot be narrowed down. P209D does not appear in any public manufacturer list; Deutz assigns the corresponding short to battery on sensor A to P2040. The SCR controller stops dosing because it can no longer confirm atomization, and the warning lamp comes on.

Likely causes

Sensor ground open at the connector or splice
Signal wire shorted to the 5 V reference or battery voltage
Sensor B output stage failed high

Symptoms

  • Warning lamp on, dosing stopped
  • Displayed air pressure stays at an impossibly high value
  • Inducement countdown on heavy vehicles if not repaired

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–450
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

P209AP209CP209BP2040

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