Powertrain, generic (extended)

P23D6 Cylinder 2 Fuel Heater Control Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P23D6 flags the control circuit of the cylinder 2 fuel heater as high. A heater driver typically checks the line both with the channel off and with it on; a level that stays near supply voltage in both states points to a control wire touching a positive feed or to a driver that no longer pulls the circuit down. Depending on the wiring, the heater then either stays energized or cannot be switched at all. Bosch documents that its Flexstart unit also diagnoses the FET switches of every heat circuit individually, and that is where a fault of this kind surfaces. P23D6 itself appears in no public manufacturer document, while CARB counts heated fuel preparation among the outputs to watch. Expect either a cold cylinder 2 at start or a heater that runs on. Low and open faults: P23D7, P23D5.

Likely causes

Cylinder 2 heater control wire touching a positive feed
Switching FET of channel 2 failed in the conducting state
Bent connector pin touching a supply terminal

Symptoms

  • Heater at cylinder 2 runs on or does not switch
  • Cylinder 2 starts cold on ethanol
  • 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 2

Related codes

P23D5P23D7P23D8P23D2P23DA

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