Powertrain, generic (extended)

P23D4 Cylinder 1 Fuel Heater Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P23D4 is not about wiring at all: the cylinder 1 heater circuit is electrically intact, yet it fails to heat as it should. The heater unit measures what each heat circuit delivers, so a heater that draws too little current, warms too slowly or reaches a lower temperature than its neighbours stands out. Bosch notes that its Flexstart unit keeps track of the heat energy put out by each of four separate circuits and reports the measured temperature to the engine module. Aging elements, deposits on a heated injector or a high-resistance contact are plausible reasons. No manufacturer documents P23D4 or its limits publicly. CARB asks for functional monitoring of heated fuel preparation. Cold starts may be rough on one cylinder; P23D1 to P23D3 cover the electrical faults.

Likely causes

Aged cylinder 1 heater with reduced heating power
High-resistance connection in the cylinder 1 heater circuit
Deposits reducing heat transfer at a heated injector
Low battery voltage during the heating phase

Symptoms

  • Cylinder 1 runs rough for a while after a cold start on ethanol
  • Longer cranking in cold weather
  • Engine warning lamp, depending on manufacturer

Repair estimate

DifficultyHardWorkshop job
Parts and labour€80–600
Time1–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

fuel heater cyl 1

Related codes

P23D1P23D2P23D3P23D8P23CE

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