Please help!!! Codes?? 96 Cavalier

My 96 Cavalier does not swith gears on its own. It is an automatic and about a month ago, it started. I have to let my foot off the gas then push on it again in order for it to switch. Otherwise, the RPM gauge goes past 4 and it will not switch gears. A mechanic suggested it was the knock sensor and it was replaced, but no change. I'm in Okinawa, Japan so this car is foreign to the mechanics here. They suggested I find trouble codes online and that may be able to help them. I don't know what else to do. Please help if you have ANY suggestions. Thank you!