One problem related to service engine light on has been reported for the 2010 Ford Focus. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2010 Ford Focus based on all problems reported for the 2010 Focus.
While driving at around 15 mph, my car started to accelerate even though my foot wasn't on the gas. I looked at my dash to confirm cruise control was not on (it wasn't) and noticed the service engine light was on. If I didn't touch the gas or brake the car would accelerate up to 30 mph and stay constant at that speed. I rode the brakes to the local Ford dealer. They inspected the car and determined the issue was the throttle body sensor, and said I had to replace the entire throttle body. Cost was $400 for the part and $230 for labor. This was not covered on the powertrain warranty I still have.