Powertrain, generic (extended)

P23CF Fuel Heater Control Module Feedback Signal Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P23CF is logged when the feedback line from the fuel heater control unit stays near ground, below its valid signal range. Mostly the wire is chafed against ground or the feedback output inside the unit is shorted. Depending on how the signal is coded, a permanently low level can also look like a heater that never reports a result, which is why the engine module treats it as a circuit fault rather than as real data. No manufacturer documents P23CF publicly; the background is the temperature and diagnostic feedback that Bosch describes for its Flexstart heater unit. CARB requires the inputs of monitored emission components to be checked for out-of-range values. Cold-start heating may be suppressed. The high-side counterpart is P23D0, a missing signal P23CD.

Likely causes

Feedback wire shorted to ground
Moisture in a connector of the feedback circuit
Shorted feedback output in the fuel heater control module
Faulty input stage in the engine control module

Symptoms

  • Fuel heating not used for cold starts
  • Long cranking with ethanol in cold weather
  • 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

P23CDP23CEP23D0P23C8

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