Powertrain, generic (extended)

P23DF Cylinder 4 Fuel Heater Control Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P23DF marks the cylinder 4 heater control circuit as low, which in practice is a short to ground between the control unit and the heater. The channel then stays off until the next start. On four-cylinder engines cylinder 4 is the outermost rail outlet, where the harness often passes brackets and hot components; chafed insulation there, a heating element shorted to its housing and moisture in the plug are the usual suspects, an internally shorted output in the control unit less so. No manufacturer documents P23DF publicly; the CARB rule expects such outputs to be checked for circuit faults. In daily use the fault shows as a rough cold start on one cylinder, sometimes together with a tripped fuse. Its high counterpart is P23DE, the open circuit P23DD.

Likely causes

Chafed insulation on the cylinder 4 heater lead at the rail end
Heating element at cylinder 4 shorted to its housing
Moisture in the cylinder 4 heater plug
Shorted channel 4 output in the heater unit

Symptoms

  • Rough cold start on one cylinder
  • Tripped fuel heater fuse
  • 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

P23DDP23DEP23E0P23DBP23D3

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