Troubleshooting Introduction (BMW 3 Series E46)

A car owner who follows the standard service intervals will not have to use this section of the manual very often. The reliability of branded parts is such that if you inspect or replace parts and components subject to wear at the specified intervals, then a sudden breakdown is unlikely. Malfunctions can occur not only as a result of a sudden breakdown, but also due to the accumulation of damage over time. Serious malfunctions are usually preceded by characteristic signs hundreds or even thousands of kilometers before the breakdown. Those components that sometimes fail without warning are usually small in size and can 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 (and its symptoms) will disappear, but he will not know what to do if the fault occurs again and he may end up spending more time and money than necessary. A calm and logical approach will end up being cheaper.

Always take note of any signs of abnormal operation that may have been noticed during the time period preceding the malfunction, such as loss of power, high or low instrument readings, unusual odors, etc. Remember that failure of 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 troubleshoot a fault, who may not have described the fault very accurately.

Don't miss the obvious

For example, if the car does not start, check if there is petrol in the tank? (Don't rely on anyone's words and don't trust the fuel level indicator!). If you have a problem with an electrical circuit, look for a loose connection or broken wire before you get out the 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 also quickly discharge. Likewise, replacing spark plugs contaminated with oil will allow you to continue driving, but you should remember that the cause of contamination (except for the use of unregulated candles) is not excluded - it needs to 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 lying in the trunk for months), and in the troubleshooting sequence, don't skip components 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.