Malfunctions can occur not only as a result of sudden failure, but also due to the accumulation of damage over time. Serious failures are usually preceded by characteristic signs hundreds or even thousands of kilometers before the failure. Those components that sometimes fail without warning are usually small in size and easily fit in the trunk.
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 much may get lucky and find the fault (or its symptoms) will disappear, but he will not know what to do if the fault occurs again and may end up wasting more time and money than necessary. A calm and logical approach will be cheaper in the long run. Always take note of any signs of abnormal operation that may have been noticed in the period preceding the fault – loss of power, high or low instrument readings, unusual odours, etc. – and remember that faulty components such as fuses or spark plugs may only be a consequence of underlying faults.
These pages contain 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 chapters and sections in brackets that contain descriptions of 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, make sure there's gas in the tank? (Don't rely on anyone's words and don't trust the fuel indicator!) If you have a problem with an electrical circuit, look for a loose connection or broken wire before you get out your tester.
Treat the disease, not the symptoms. Replacing a dead 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 soon become discharged too. Likewise, replacing spark plugs contaminated with oil will allow you to continue your journey, but you should remember that the cause of the contamination (unless it was the wrong type of candles) remained and it must be identified and eliminated.
Don't take anything on faith. Especially, remember that a "new" component may be defective from the start (especially if it's been lying in the trunk for months) and don't skip components in the troubleshooting sequence just because they are new or recently installed. When you finally find the source of a difficult problem, you'll probably realize that it was obvious all along.