Whenever a fault occurs, the first step is to decide where to start looking. Sometimes this is obvious, other times it is not. An owner who has made half a dozen adjustments or replacements without thinking may be lucky and the fault (or its symptoms) will disappear, but he will not know what to do if the fault reoccurs and he may end up spending more time and money than necessary. A calm and logical approach will cost less in the long run. Always take note of any signs of abnormal operation that may have been noticed in the time period preceding the fault - such as loss of power, high or low instrument readings, unusual odours, etc. Remember that faulty components such as fuses or spark plugs may only be a consequence of underlying faults.
These pages provide recommendations to help you find the most common faults that may occur when operating your vehicle. These faults and their possible causes are grouped under headings that represent the various components or systems of the vehicle, such as the engine, cooling system, etc. The possible causes of the faults are followed by the chapters and sections in brackets that contain the appropriate repair procedures. The following basic principles apply when finding and determining faults:
Make sure there is a fault. You should know exactly what the symptoms of a fault are before you begin work. This is especially important if you are helping someone else find a fault, who may not have described the fault very accurately.
Don't miss the obvious. For example, if the car won't start, check to see if there's gas in the tank. (Don't rely on anyone's word or the fuel gauge!) If there's a fault in the electrical circuit, look for a loose connection or broken wire before you get out the tester.
Treat the disease, not the symptoms. Replacing a discharged battery with a fully charged one will relieve you of the problem for a while, but if you do not find the cause of the discharge, the new battery will also quickly discharge. Likewise. replacing oil-contaminated spark plugs will allow you to continue driving, but you should remember that the cause of contamination (except for the use of non-regulated spark plugs) is not excluded - it must be identified and eliminated.
Don't take anything on faith. Remember, in particular, that a "new" component may have an "inherent" defect (especially if it's been sitting in the trunk for months), and don't skip components in the troubleshooting sequence just because they're new or recently installed. When you finally find the source of a difficult problem, you'll probably realize that it was obvious all along.