What if you don't have any codes stored and you still have a performance issue with your vehicle? This is where things can get a bit tricky. One of the first things I do is try to nail down the system where the problem is originating. It could be an engine or transmission problem, or something else, such as an issue with the final drive. It could also be a problem with the brakes, the tires, the engine mounts, or any number of things. One of the first things you can do is determine if it's an engine problem or an automatic transmission problem. If you have a manual transmission, this test won't work for you.