I have a 1997 Toyota Avalon XLS, Miles are 155,239.
I had the engine check light come on and had it checked by a friend who had a meter who works at a Toyota dealership- it showed that I had a faulty transmission shift solenoid.
The shift solonoid is internal to the transmission. You have to know which one. There is more one. Have your friend find out which one. It should be done by a tranny person. If you aren't have shifting problems you will soon with a defective shift solonoid.