Powertrain, generic (extended)

P23DE Cylinder 4 Fuel Heater Control Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P23DE means the cylinder 4 heater control circuit is at a high level where the module expects otherwise. Either the line has contact with a voltage source, or the driving stage no longer switches off, so heater 4 may keep running. The risk lies less in starting than in overheating: Bosch states that its heated rail works with fuel temperatures from 70 up to 125 °C depending on system pressure, and that the heating element can tell when it is running in air or vapour. If cylinder 4 keeps heating once the engine is warm, vapour bubbles form at that outlet and hot restarts can suffer. No manufacturer documents P23DE publicly; CARB requires circuit monitoring. Low fault: P23DF, open: P23DD, performance: P23E0.

Likely causes

Channel 4 driver no longer switching off
Cylinder 4 heater line touching a voltage source
Connectors swapped or mismated after repair

Symptoms

  • Hard restart when the engine is hot
  • Uneven idle after hot soak
  • Engine warning lamp, depending on manufacturer

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–500
Time0.5–2.5 h

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

Parts involved

fuel heater cyl 4

Related codes

P23DDP23DFP23E0P23DAP23D2

References: bosch-mobility.com, law.cornell.edu.