Powertrain, generic (extended)

P23C7 Fuel Heater Control Module Power Control Circuit/Open

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

Flex-fuel engines that must start on high-ethanol blends in the cold warm the fuel before injection, and a separate heating control unit switches the high heater currents on command of the engine module. P23C7 reports that the power control line to this unit is open or electrically faulty, so the heaters cannot be enabled. No manufacturer documents P23C7 publicly. Bosch describes its Flexstart heating control unit with a built-in relay for the heating current and full open/short diagnostics, and notes that ethanol ignites poorly below about 13 °C. CARB names heated fuel preparation systems as output components that need circuit monitoring. Expect long cranking or no start on ethanol in cold weather; P23C8 and P23C9 are the low and high cases.

Likely causes

Broken or disconnected power control wire between engine module and heater unit
Blown fuse or failed relay feeding the heater control circuit
Corroded or loose connector at the fuel heater control module
Internal fault in the fuel heater control module

Symptoms

  • Hard or failed cold starts on high ethanol blends
  • Rough running right after a cold start
  • Engine warning lamp, depending on manufacturer

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–600
Time0.5–2.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

fuel heater control module

Related codes

P23C8P23C9P23CDP23CAU01B6

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