Unfortunately it looks like you have no way of reading codes on your tractor without dealer computer. I believe that was not available for your model until a later year model. THe Service Advisor connection on your tractor is behind the seat. There should be a panel behind the seat held down with 2 thumbscrews. Remove that panel and on left side under cover is a large round black connector. That is where you plug in to do diagnostics. There is a performance monitor that can be bought to plug in to do diagnostics and calibrate hitch. Monitor and wiring harness to plug into diagnostic plug runs near $2000.00. If you have diagnostic manual, it will tell you how to use monitor to diagnose.