Powertrain, generic (extended)

P23D7 Cylinder 2 Fuel Heater Control Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

For P23D7 the module reads the cylinder 2 heater control line as low, which on these power circuits nearly always means a path to ground: a chafed wire, a heater element shorted to its body, or fuel or water bridging the connector pins. The short draws more than the channel is meant to carry, so the heater unit protects itself; Bosch mentions reverse-voltage and internal overtemperature protection as well as short detection per circuit. In practice the heater on cylinder 2 is switched off and that cylinder starts cold while cylinders 1, 3 and 4 still get warm fuel; a blown heater fuse is possible. No manufacturer documents P23D7 publicly; CARB demands circuit checks on this output. High and open on cylinder 2: P23D6, P23D5; cylinder 1 equivalent: P23D3.

Likely causes

Cylinder 2 heater wire chafed through to ground
Heating element at cylinder 2 shorted to its housing
Fuel or water bridging pins in the cylinder 2 heater plug

Symptoms

  • Rough cold start on one cylinder
  • Fuel heater fuse blown
  • 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

P23D5P23D6P23D8P23D3P23DB

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