Wrench light on dash on 2005 Ford F-250 Super Duty

I recently purchased my 2005 F250 Crew cab FX4 King Ranch 4x4 with 50,000 miles on it. After driving for a few weeks I noticed a wrench light on the dash. It only comes on while highway driving for around 15-20 miles and seems to be triggered when the brakes are applied hard when traffic slows suddenly or coasting to slow down. There is no loss of power or unusual noises or even smoke. When the engine is shut off the light doesn't return until a similar situation occurs. I live alone and this is my only transportation. I work long hours and will have to take a day off from work to get it diagnosed at Ford as well as costing me $100 deductible on my warranty. The previous owner told me he took the vehicle in for this light and I see on car fax that it was services at $8,000 mile. he also said that Ford told him that these lights come on sometimes for no reason. Is this true and is there a common cause for this that I can fix and avoid loss of work and a deductible?