Powertrain, generic (extended)

P23DB Cylinder 3 Fuel Heater Control Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

With P23DB the cylinder 3 heater control circuit is too low, meaning the line or the heater itself has found a path to ground. Because a single heat circuit is sized for several hundred watts, such a short trips the current limit at once; Bosch describes short detection per circuit and an integrated current relay in its Flexstart unit, which then cuts only the affected channel. Cylinder 3 starts on cold fuel while the remaining heaters keep working, so the engine shows roughness on one cylinder rather than a general cold-start problem. Water entering the connector, a damaged harness clip near the rail or an internally shorted heated injector are plausible causes. No manufacturer documents P23DB publicly; CARB requires circuit monitoring. Related: P23DA, P23D9, P23DC.

Likely causes

Water in the cylinder 3 heater connector
Harness chafed through at a damaged clip near the rail
Heated injector at cylinder 3 shorted internally

Symptoms

  • One-cylinder roughness when starting cold
  • Other cylinders start normally
  • 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 3

Related codes

P23D9P23DAP23DCP23D7P23DF

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