Powertrain, generic (extended)

P204A Reductant Pressure Sensor Circuit

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P204A is the general electrical fault of the sensor that measures DEF pressure between pump and injector; in most systems it is built into the pump module. The secondary ECU of Deutz's EMR L1 uses it for two states that are neither low nor high: a ground fault (failure type F0) and a sensor supply outside its window (1C), while shorts to ground or battery go to P204C and P204D. Mack trucks to US13 emissions report P204A-13 for an open signal or ground wire; repair instruction GDC18-058 has the harness checked and otherwise lists the complete DEF pump unit as the part to fit. Without a valid pressure value the controller cannot regulate dosing, so it stops the pump and the inducement timer starts. CARB requires such inputs to be monitored for circuit faults.

Likely causes

Open signal or ground wire to the pressure sensor
Sensor supply voltage out of range
Pressure sensor inside the DEF pump unit failed

Symptoms

  • MIL on, DEF system warning
  • No DEF dosing
  • Power or speed limitation after the countdown

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€100–1,200
Time0.7–3 h

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

Parts involved

reductant pressure sensorreductant supply line

Related codes

P204BP204CP204DP204E

References: serdia.deutz.com, serdia.deutz.com, static.nhtsa.gov, law.cornell.edu.