In between my other activities, I enjoy reading forum posts where George, Barney and Elmer try to diagnose a modern vehicle without a scan tool. The stories are all the same. They go on eBay or another site, buy a part, put it on and nothing changes. Same problem.
Modern vehicles are computer controlled with complex software that controls systems. In many cases, the fault code will prevent the system from restarting and must be cleared before the system will resume normal operation. The days of repairing vehicles with a screwdriver and a monkey wrench are gone.
A 1977 Chevrolet Nova and a 2016 Toyota Camry are not the same. One post that really got me was a guy who put a circuit board (conductor plate) in a 2002 Mercedes and after all the work, the transmission still wouldn't shift. After his third conductor plate and drain/fill of transmission oil, he asked for help. I advised him to clear the codes then drive the vehicle
He found a mobile mechanic who cleared the codes and the vehicle drove like new. This vehicle had been out of service for a year due to the lack of knowledge and trying this and that.
A good scan tool is the first tool in a modern vehicle toolbox.
