Po742

2nd post : 2001 Buick Century 112000 miles. I took this car to a transmission shop for this problem(very good shop) they checked the transmission out and told me it was working fine and if I could live with the check engin light, drive it! This was about a month ago and the check engin light comes on about every week or ten days. The fluid has been changed every 50000 miles. Is there a good product to add to the fluid that might help this problem. Could this be an external wiring problem? If so where or what would you clean? Thanks Ernie