2003 Honda Odyssey check engine light?

My customers have an 03 Honda Odyssey with 98K miles on it. Yesterday the check engine light came on and today when my customers drove it my customers noticed that it revved a lot before shifting into the next gear. And a couple of times after stopping at a light or a stop sign it wouldn't go when my customers stepped on the accelerator Car Diagnostic Tools. It just sounds like the wheels are spinning but it doesn't want to go. Any clues? My customers really don't want to replace a transmission right now. Someone please tell me that's not what it is!