P204AReductant Pressure Sensor Circuit
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- 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.
- What you may notice
- MIL on, DEF system warning
- No DEF dosing
- Power or speed limitation after the countdown
- Likely causes
- LikelyOpen signal or ground wire to the pressure sensor
- PossibleSensor supply voltage out of range
- PossiblePressure sensor inside the DEF pump unit failed
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €100 – €1,200
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.