Powertrain, generic (extended)

P204B Reductant Pressure Sensor Circuit Range/Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

P204B is a plausibility test: the DEF pressure sensor is electrically fine, but its value disagrees with the system state. GM uses moments when the true pressure is known. The 6.6 L LML sets it if more than 50 kPa appears while the line is empty and unpressurised (Type A, Type B on the 2014 Cruze diesel); GM's 2018 diesel table compares the reading with ambient after the end-of-trip purge, and GM's 2025 DEF controller fails it when the value strays more than 36.4 kPa from ambient before priming. Deutz marks the case on the EMR L1 with failure type 64. Hino released new DCU software in 2016 (SB-16-015) because the unit stored P204B falsely on conventional trucks. A genuine offset mostly means an ageing sensor in the pump module.

Likely causes

Pressure sensor offset drift inside the pump module
Dosing control unit software misjudging the reading (Hino SB-16-015)
Line not emptied at shutdown, e.g. afterrun interrupted or frozen DEF

Symptoms

  • MIL on, possibly only after a second trip
  • Emission service message
  • Often no noticeable driveability change

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€0–1,200
Time0.5–3 h

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

Parts involved

reductant pressure sensor

Related codes

P204AP204CP204DP204EP20E8

References: gsi.ext.gm.com, gsi.ext.gm.com, gsi.ext.gm.com, serdia.deutz.com.