Powertrain, generic (extended)

P23D1 Cylinder 1 Fuel Heater Control Circuit/Open

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

Instead of one heater for the whole rail, some flex-fuel systems give every cylinder its own heating path, either a heated injector or an element at each rail outlet. P23D1 is the open or general circuit fault on the path for cylinder 1, so that cylinder gets unheated ethanol during a cold start. Bosch's Flexstart heating control unit supervises four separate heat circuits of about 260 W each and recognises interruptions, which matches this per-cylinder layout. No manufacturer documents P23D1 publicly. CARB lists heated fuel preparation as an output component to be monitored. Typically cylinder 1 misfires or contributes nothing in the first seconds after a cold start. Cylinders 2 to 4 follow from P23D5 onwards; a rail-wide heater uses P23CA.

Likely causes

Burnt-out heater at cylinder 1 (heated injector or rail element)
Broken wire or unplugged heater connector at cylinder 1
Corroded terminals in the cylinder 1 heater connector
Failed channel 1 output in the fuel heater control module

Symptoms

  • Cylinder 1 misfire right after a cold start on ethanol
  • Rough idle until the engine warms up
  • Engine warning lamp, depending on manufacturer

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–500
Time0.5–2.5 h

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

Parts involved

fuel heater cyl 1

Related codes

P23D2P23D3P23D4P23D5P23CA

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