Why does the ford transit traction control light stay on?

Contrary to what some other people may be saying here, the most common reason that Your traction control light is staying on is a fault in the ABS system. This applies to the Ford Transit, as well as most other vehicles. There are a number of things that could go wrong with the ABS, so I'll briefly touch on a few of them here. More than likely, what's at fault is a failed wheel speed sensor. These are relatively inexpensive, and can be swapped out by most auto enthusiasts with even a little bit of know how. However, You may have some deeper problems. The sensors get their readings from magnetic or grooved plates called tone wheels -- if Your tone wheel is shot, You'll likely have to replace Your bearing or hub assembly. It's best to start at the cheapest thing and work Your way up. You'll first want to get access to an OBD-II device and see what trouble codes, if any, Your Transit is throwing.