Powertrain, generic (extended)

P23DD Cylinder 4 Fuel Heater Control Circuit/Open

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P23DD reports an open or general fault on the fourth and last heating channel. Bosch builds its heater unit with exactly four heat circuits and its heated rail for either three- or four-cylinder operation, so this code belongs to four-cylinder layouts. There the usual culprit is a heater at cylinder 4 that has burnt through or a plug that came loose during work on the intake manifold; a dead channel in the control unit itself is less likely. No manufacturer documents P23DD publicly, and CARB treats heated fuel preparation as an output that must be monitored. The engine then starts with one cold cylinder and runs unevenly on it for the first seconds, especially with high ethanol content. The shorts on this path are P23DE and P23DF.

Likely causes

Burnt-through heater at cylinder 4
Heater plug at cylinder 4 left loose after intake work
Dead channel 4 in the heater control unit

Symptoms

  • Uneven running on one cylinder for the first seconds after a cold start
  • Worse with high ethanol content
  • 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

P23DEP23DFP23E0P23D9P23D1

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