The better you're able to communicate your car's symptoms, the easier it is for the mechanic to diagnose and fix the problem. Write down what you hear, feel, see, and smell before you arrive and keep a log of exactly when the symptoms occur (for instance, when you're braking or when you're driving over a certain speed), and share this with your mechanic. Also, note the location and frequency of the symptoms, and if any repairs were done on the vehicle recently. Sometimes a problem is related to the last repair. Go online to a website, such as AutoMd.com, which can help you diagnose your car’s problem and see a list of questions your mechanic might ask.