Powertrain, generic (extended)

P23C9 Fuel Heater Control Module Power Control Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P23C9 is stored when the power control line to the fuel heater control unit shows battery voltage although the engine module has it switched off, pointing to a short to a live wire. The real risk here is the reverse of the low case: the heater stage may be enabled without being asked, warming the fuel after it is no longer needed and loading the electrical system. No manufacturer documents P23C9 publicly. Bosch lists reverse voltage and internal overtemperature protection for its Flexstart heating unit, which limits damage, and the engine module normally only heats depending on ethanol content and outside temperature. CARB requires output circuits of heated fuel systems to be checked. P23C7 covers the open and P23C8 the low fault.

Likely causes

Power control wire shorted to a battery or ignition feed
Welded relay contact keeping the circuit energized
Internal leakage in the fuel heater control module
Engine module output that does not switch off

Symptoms

  • Fuel heating active when not needed, possible battery drain
  • Heater unit or wiring gets unusually warm
  • 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

P23C7P23C8P23D0P23CC

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