P23DDCylinder 4 Fuel Heater Control Circuit/Open
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- P23DD reports an open or general fault on the fourth and last heating channel. Bosch builds its heater unit with exactly four heat circuits and its heated rail for either three- or four-cylinder operation, so this code belongs to four-cylinder layouts. There the usual culprit is a heater at cylinder 4 that has burnt through or a plug that came loose during work on the intake manifold; a dead channel in the control unit itself is less likely. No manufacturer documents P23DD publicly, and CARB treats heated fuel preparation as an output that must be monitored. The engine then starts with one cold cylinder and runs unevenly on it for the first seconds, especially with high ethanol content. The shorts on this path are P23DE and P23DF.
- What you may notice
- Uneven running on one cylinder for the first seconds after a cold start
- Worse with high ethanol content
- Engine warning lamp, depending on manufacturer
- Likely causes
- LikelyBurnt-through heater at cylinder 4
- PossibleHeater plug at cylinder 4 left loose after intake work
- RareDead channel 4 in the heater control unit
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €60 – €500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.