P21BBCold Start Cylinder 6 Injection Timing
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- Cylinder 6 exists on six-cylinder engines and anything larger – inline sixes and V6 units such as Ford's 3.5-litre EcoBoost petrol or the 3.0-litre EcoDiesel in the Ram 1500. For that diesel FCA listed the warm-engine timing codes P020A–P020F together with the over-advanced and over-retarded codes in a 2021 bulletin whose fix was reprogramming the engine module. P21BB is the cold-start version for cylinder 6: during the heating phase after start, its injection timing did not match the target. Diesels adapt injection timing to coolant temperature after a cold start to hold emissions down before NOx sensors are working, as a GM patent describes. No manufacturer documents P21BB publicly; a software update is worth checking before replacing parts.
- What you may notice
- Check engine light after cold starts
- On diesels, more white smoke or knocking in the first minutes
- Hard start or rough idle when cold
- Likely causes
- LikelyInjector of cylinder 6 worn, coked or with drifting opening delay
- PossibleOutdated engine module software (analogous timing codes were cured by reprogramming)
- PossibleDamaged wiring or connector at injector 6
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €100 – €1,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.