Answer: Again, since 1996, all vehicles built to be sold in the United States have on-board diagnostics that monitor engine’s performance and inform drivers of problems. Your vehicle basically monitors and diagnoses its own performance. However, you can purchase your own computer or scanner to check for problems with your engine. These are the same scanners that technicians use to receive and diagnose problems stored by your OBD-II System. You can purchase one of these scanners and periodically check your engine’s performance, or you can rely on your OBD-II System and have your vehicle inspected by a trained technician whenever your “check engine” light comes on.