Powertrain, generic (extended)

P23D2 Cylinder 1 Fuel Heater Control Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P23D2 is the high-voltage fault on the cylinder 1 heater circuit; note that in this series the high code comes before the low code (P23D3). The control side of the heater shows supply voltage while it should be switched off, so the switching stage has lost control: a short to a positive wire or a switching element that no longer turns off are the usual reasons. A heater left energized keeps warming fuel at cylinder 1 after start and draws current constantly. No manufacturer documents P23D2 publicly. Bosch credits its Flexstart heater unit with diagnosing the switching FETs of each of its four heat circuits, which is the kind of check behind this code. CARB requires circuit monitoring of heated fuel preparation. Opens are P23D1.

Likely causes

Cylinder 1 heater control wire shorted to a positive feed
Channel 1 switching element stuck on in the heater unit
Damaged connector letting the heater pin touch a supply pin

Symptoms

  • Cylinder 1 heater stays on, higher current draw
  • Possible hot-restart problems
  • 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 1

Related codes

P23D1P23D3P23D4P23D6

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