Ford F350 6L diesel trucks are compliant with the OBD-II (onboard diagnostic) codes mandated by law. The truck’s computer operates an OBD system that diagnoses problems automatically. So, if the check engine light illuminates on the dashboard, you will need to access the computer and read the code. All you need is an OBD-II scanner, available at any auto-parts store.
Connect the OBD-II handheld to the diagnostic jack. This outlet will be on the driver’s side, near the steering column.
Turn the handheld on.
Place the key into the F350′s ignition and turn the truck on.
Wait a few seconds as the handheld and the truck’s computer talk to each other.
Write down the code that pops up on the handheld. You can reference the codes online through automotive OBD-II coding sites, or by merely typing the trouble code into Google, Bing, Ask or another search engine.