P204C code meaning
Reductant Pressure Sensor Circuit Low
Powertrain system Generic code P20xx codes Check engine light
What P204C means
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.
P204C at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium
- Typical labor0.5 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P204C
- MIL on
- DEF dosing stopped, DEF warning messages
- Further reductant codes stored at the same time
Common causes of P204C
- Most 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
- Less likelyFailed sensor in the pump/heater assembly
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Reductant pressure sensor
What each part of P204C means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 0 | Area: fuel and air metering and auxiliary emission controls. |
| 4C | The exact fault in that area. |
What to do next
- Note P204C and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P204C
What does P204C mean?
P204C means "Reductant Pressure Sensor Circuit Low". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P204C?
Drive gently and only to a workshop. With P204C the car can go into limp mode (reduced power) to protect itself.
Will P204C fail an emissions test?
Yes, it can. P204C is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P204C to fix?
Difficulty: medium. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will P204C clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.