The extension is just a cable so that you can sit in the drivers seat and use the code reader from there. It doesn't take long at all to use and it's got tons of features. I think other than just regular codes the best thing is the cylinder balance test, which cuts fuel to each cylinder one at a time to test for lack of power from each one. You can use it to test for headgasket leaks and compression tests, it'll all show with the balance test.