GENERAL AUTOMOTIVE DIAGNOSTICS
by Mark Davidson

This website is designed help you learn about and diagnose your vehicle: car, truck, van, or Sport Utility Vehicle (SUV). This site contains a wealth of information that will help you learn and understand how your vehicle operates. Although your vehicle functions as a whole, it is really numerous systems working together to accomplish its goal.

Successful diagnosis is the result of an organized diagnostic approach. There is no magic wand available to wave over the hood that will instantly pinpoint the problem. OBD-II trouble codes offer only a clue as to what may be causing a particular problem with your car. An OBD-II trouble code, once extracted from your vehicle's onboard computer, should be looked up in a chart and used in conjuction with other data such as symptom observables, history of the problem in question, TSB's (Technical Service Bulletins), etc in order to reach an accurate diagnosis. A single symptom can be caused by numerous components on the vehicle. An accurate diagnosis should isolate the failed component. Sometimes however, it is more cost effective to replace the most suspect part and then spend the time or money on further diagnosis. Only you will be able to determine at what point this is.

Special tools are often required to work on late model vehicles. Often these tools can be rented or purchased for a nominal fee (in relation to having the work done). You should consult your local parts store for information regarding the availability of special tools or test equipment. When special tools or equipment are used, follow the tool manufacturers instructions for proper usage.

Servicing, diagnosing, and learning about your vehicle can be a rewarding challenge. Take the time to understand your vehicle by reading the associated articles for the system being serviced. It is money well spent to invest in the official manufacturer's manual which covers your particular make and model vehicle. This manual was written by the engineers which actually designed your vehicle, thus it is the most authoritative reference for your vehicle. Such a manual may cost well over $100.00 but it will help lead to accurate diagnosis of almost anything which can go wrong with your vehicle. Contact your nearest dealer parts department to purchase a manufacturer's manual which covers your make and model car.

Once you gain a working knowledge of how your vehicle operates, you are in a much better position to diagnose it. As you can see from the sub-topics of each section, there are many components that comprise each system of the vehicle. Each component accomplishes a specific goal. When a component fails, it fails to accomplish its goal and results in degraded vehicle performance and a symptom. There are less symptoms than components. In other words, many different components can fail and cause the same symptom. A leaking wheel cylinder, leaking caliper, or defective master cylinder can all manifest themselves with the same symptom, a low brake pedal or a brake warning lamp that remains on.

Visual inspection is the most effective diagnostic tool (along with OBD-II trouble codes). Once a symptom is selected, the diagnostic section usually prompts you to perform a visual inspection. It will also instruct you on specifically what to look for. Take time to look over each item carefully.

Read over the symptom diagnostic section carefully. Once you have determined what system you are diagnosing, you should familiarize yourself with the system by reading over each components theory and operation. You can access this information by clicking on the appropriate vehicle section or by searching this website for the component name. Do all this prior to opening the hood! Often by reading the theory and operation of each component, you can isolate the cause much more quickly, enabling you to efficient auto repair procedures.

(Mark gave up on sports when the Browns left Cleveland and now spends his Sundays working under a shade tree in the back yard tuning his son's soap box derby car.)