Powertrain, generic (extended)

P204C Reductant Pressure Sensor Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Water intrusion in the reductant harness connectors (Ford TSB 19-2315)
Signal wire open or shorted to ground
Missing 5 V reference to the sensor
Failed sensor in the pump/heater assembly

Symptoms

  • MIL on
  • DEF dosing stopped, DEF warning messages
  • Further reductant codes stored at the same time

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–1,500
Time0.5–4 h

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

Parts involved

reductant pressure sensor

Related codes

P204AP204DP204BP204E

References: gsi.ext.gm.com, gsi.ext.gm.com, fordservicecontent.com, static.nhtsa.gov.