P204CReductant Pressure Sensor Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P204C means the DEF pressure sensor output has fallen below its valid range, which points to an open signal wire, a short to ground or a missing 5 V supply. On the 6.6 L LML, GM fails anything under 0.41 V lasting 0.4 s, GM's 2018 diesel table a raw value under 5 % of the supply, and the 2025 DEF controller less than 0.45 V in 6 of 100 samples, each Type A. Ford's 2023 diesels set it under 0.2 V. On 2017 to 2019 Super Duty trucks with the 6.7 L, Ford (TSB 19-2315) found water entering connectors C3613 and C4851 of the reductant harness and replaced harness, pump/heater assembly or tank. Deutz uses failure type 11 for it on the EMR5. Lacking a pressure value, the controller suspends dosing.
- What you may notice
- MIL on
- DEF dosing stopped, DEF warning messages
- Further reductant codes stored at the same time
- Likely causes
- LikelyWater intrusion in the reductant harness connectors (Ford TSB 19-2315)
- PossibleSignal wire open or shorted to ground
- PossibleMissing 5 V reference to the sensor
- RareFailed sensor in the pump/heater assembly
- 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: €60 – €1,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.