Powertrain, generic (extended)

P23D0 Fuel Heater Control Module Feedback Signal Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P23D0 applies when the return signal from the fuel heater control unit is stuck above its plausible maximum. A short to a voltage source on the feedback wire is the usual explanation; with a pull-up input in the engine module an open ground at the heater unit can produce the same picture. Because a pinned-high signal could be misread as an overheated heater, the engine module discards it and records a circuit fault instead. No manufacturer documents P23D0 publicly. Bosch's Flexstart unit is described as sending heat and diagnostic data back to the engine module, which is the signal checked here. CARB requires out-of-range detection on such monitored inputs. Fuel heating is usually switched off as a precaution. The low case is P23CF, implausible values P23CE.

Likely causes

Feedback wire shorted to a voltage supply
Missing ground at the fuel heater control module
Feedback output of the heater unit stuck high
Faulty input stage in the engine control module

Symptoms

  • Fuel heating switched off as a precaution
  • Poor cold starts on high ethanol blends
  • 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

P23CDP23CEP23CFP23C9

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