Powertrain, generic (extended)

P23C8 Fuel Heater Control Module Power Control Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P23C8 covers the case where the engine module finds the heater unit's power control line pulled to ground. The likely culprit is a chafed wire touching the body or engine, or a short inside the heater unit. Because the line is held low, the heating unit either never receives its enable or, depending on the circuit design, the fuse protecting it may blow. No manufacturer documents P23C8 publicly; the background is Bosch's Flexstart concept, in which the heating control unit drives the fuel heaters with roughly 260 W per circuit at 12 V and reports short-circuit diagnostics back. CARB requires circuit checks on heated fuel preparation. The car usually still runs on gasoline-rich fuel; cold starts with ethanol become difficult. Open is P23C7, high P23C9.

Likely causes

Power control wire chafed through to ground
Moisture in the heater unit connector creating a path to ground
Shorted control input inside the fuel heater control module
Faulty output driver in the engine control module

Symptoms

  • Long cranking in cold weather on ethanol
  • Blown fuse in the fuel heater circuit
  • 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

P23C7P23C9P23CFP23CB

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