Powertrain, generic (extended)

P23D9 Cylinder 3 Fuel Heater Control Circuit/Open

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P23D9 is the open-circuit or general circuit fault of the heating path for cylinder 3. The fuel heater control unit drives each heater through a channel of its own; when channel 3 is switched on but no load current appears, the connection to the heater is considered broken. Bosch lists interruption among the faults its Flexstart unit diagnoses on all four heat circuits, and its heated rail can be configured for three- or four-cylinder engines, so on a triple cylinder 3 is the last heated outlet. No carmaker documents P23D9 publicly; CARB names heated fuel preparation as a monitored output. Below about 13 °C ethanol ignites poorly, so it is the unheated cylinder 3 that stumbles after a cold start. High and low faults on this path: P23DA and P23DB.

Likely causes

Open heating element at cylinder 3
Terminal pushed out of the cylinder 3 heater connector
Wire broken where the harness flexes near the rail
Failed channel 3 output in the heater unit

Symptoms

  • Stumble on cylinder 3 after a cold ethanol start
  • Harder starting below about 13 °C
  • 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 3

Related codes

P23DAP23DBP23DCP23D5P23DD

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