Powertrain, generic (extended)

P23CD Fuel Heater Control Module Feedback Signal/Open

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

Besides being commanded, a fuel heater control unit reports back to the engine module, so the engine knows whether heating actually took place. P23CD indicates that this feedback line carries no usable signal or is open. Bosch describes exactly such a return path for its Flexstart unit: the delivered temperature and diagnostic status are measured and handed on to the engine module, which uses them to dose the heating energy. No manufacturer documents P23CD publicly. Without feedback the engine module cannot confirm heater operation, may stop using fuel heating and cannot evaluate the individual heater circuits. CARB requires monitoring of heated fuel preparation. Implausible feedback is P23CE; shorts of the line are P23CF and P23D0.

Likely causes

Broken feedback wire between heater unit and engine module
Loose or corroded pin for the feedback signal
Heater unit without supply or ground, so it sends nothing
Failed feedback output in the fuel heater control module

Symptoms

  • Cold-start fuel heating disabled or unconfirmed
  • Harder starts on 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

P23CEP23CFP23D0P23C7

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