Powertrain, generic (extended)

P21BB Cold Start Cylinder 6 Injection Timing

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modeNo

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.

Likely causes

Injector of cylinder 6 worn, coked or with drifting opening delay

Outdated engine module software (analogous timing codes were cured by reprogramming)

Damaged wiring or connector at injector 6

Symptoms

Check engine light after cold starts
On diesels, more white smoke or knocking in the first minutes
Hard start or rough idle when cold

Repair estimate

DifficultyHardWorkshop job

Parts and labour€100–1,500

Time0.5–4.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

fuel injectorinjector wiringengine control module

References: law.cornell.edu, static.nhtsa.gov, patents.google.com, en.wikipedia.org.