2002 C240 Trans Prob

My co-workers C240 yesterday shifted hard into reverse coming out of the garage. When driving the engine reved real high for the speed. When she was at the gas station she hit the gas good and that stopped the problems but there is now a check engine light. Today the car shifted hard into reverse again so she didn't drive.

Do I have to hook the car up to a reader to pull the code or can you retreive it from the car?

Does this problem sound familiar with anyone (aka what it could be)?