Vehicle Component and System Troubleshooting

Vehicle owners who perform routine maintenance in accordance with the schedule given in the Maintenance and Tune-up chapter of this Manual will seldom need to refer to the material in this Section. The reliability of the components installed on modern vehicles is so high that, provided worn parts and parts that have deteriorated due to material aging are replaced on time, the probability of their sudden failure is extremely low. Failures rarely occur spontaneously; they are usually the result of a defect that has developed over a sometimes lengthy period. In particular, the failure of mechanical components is almost always preceded by the onset and development of characteristic symptoms, which may appear many thousands of kilometers before the failure. Components that may fail unexpectedly are usually not vital to the operation of the main units and systems of the vehicle, or they can be easily replaced under roadside conditions.

The fundamental step in identifying the cause of any failure is selecting the starting point of the investigation. The cause is often obvious; in some cases, however, a small amount of investigation is required. A car owner who carries out a half-dozen random checks, replacements and repairs may well find the cause of the failure (or its symptom), but this approach cannot be considered reasonable, as it is labor-intensive and wastes time and money. A calm, logical approach to locating the failed unit or component is far more effective. Be sure to take into account all symptoms and warning signs that preceded the failure, even minor ones, such as loss of engine power, changes in gauge readings, unusual noises and odors, etc. Do not forget that the failure of components such as fuses or spark plugs may be only a symptom of a more deeply hidden malfunction.

The following subsection contains a fairly simple chart for diagnosing the most common failures. Causes of malfunctions and their symptoms are grouped by the unit or system whose operation they affect: “Engine”, “Cooling System”, etc. References to the relevant Chapters and Sections of this Manual covering the operation of the suspected components are given in parentheses.

Regardless of the nature of the failure, the following basic principles always apply when investigating its cause:

Make sure the failure symptoms are correctly identified. This means being certain of the boundaries of the search area, which is especially important when another car owner who cannot accurately describe the symptoms is assisting with diagnosis.

Do not overlook obvious faults. For example, if the engine will not start, do not hesitate to check for fuel in the fuel tank (and do not take the word of the owner of the faulty vehicle on trust). In the event of an electrical failure, first check the condition and security of the wiring terminal connections; only after that is it worth using diagnostic equipment.

Try to eliminate the cause of the failure, not its symptom. Replacing a discharged battery with a new one will allow the engine to start, but the cause of the discharge of the old battery will remain unresolved, which will quickly lead to the failure of the new one as well. Likewise, replacing spark plugs fouled with oil will restore engine operation for a while, but the failure will inevitably recur soon (unless the cause was simply the use of plugs of the wrong type).

Do not accept any statements on trust. Remember that a “new” component may also be faulty, especially if it has been lying in the trunk for a long time. Do not exclude a component from the list of items to check just because it is new or has been recently installed. If this recommendation is ignored, do not be surprised when the cause of the failure, finally identified, turns out to have been obvious from the very beginning.