Powertrain, generic (extended)

P23D5 Cylinder 2 Fuel Heater Control Circuit/Open

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

Cylinder 2 has its own fuel heating path on flex-fuel engines that warm the fuel per cylinder, and P23D5 says this path carries no current although the heater is commanded on, or the control line shows a general fault. To the heater unit the open simply looks like a missing load on channel 2. Bosch describes its Flexstart unit as checking each of four heat circuits for interruption and shorts and passing the result to the engine controller. No carmaker publishes P23D5 or its limits. CARB lists heated fuel preparation among the output systems to be monitored. Cylinder 2 then receives cold ethanol during the first seconds of a cold start. A quick check is to compare the resistance of heater 2 with that of its neighbours. Shorts on the same path are P23D6 and P23D7.

Likely causes

Heater at cylinder 2 burnt through (open element)
Cylinder 2 heater plug loose or not latched after intake work
Broken conductor in the cylinder 2 heater lead
Channel 2 output of the heater control unit failed

Symptoms

  • Cylinder 2 misfires briefly after a cold start on ethanol
  • Uneven idle in the first minute when cold
  • 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 2

Related codes

P23D6P23D7P23D8P23D1P23D9

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