Troubleshooting electrical equipment (BMW 5 Series E39)

When troubleshooting an electrical system, a systematic approach is important. This applies to both checking failed incandescent lamps and checking non-working electric motors.

If an electrical component is protected by a fuse, the first step is to check the fuse. The location of the correct fuse is determined by the diagram located under the fuse cover in the glove compartment and on the back of the right side trim of the luggage compartment (see also chapter "Replacing fuses").

The defective fuse is replaced and after switching on the power consumer it is necessary to check whether the fuse does not immediately burn out again. If the fuse burns out again, the fault must be found and eliminated, as a rule, it is a short circuit. This means that in some place, perhaps also inside the device, the ground and the positive conductor are connected to each other.

The second step of checking: if the incandescent lamp does not light or the electric motor does not work with a good fuse, it is necessary to check for the presence of supply voltage.

Checking an incandescent lamp

Remove the bulb and inspect it. If the bulb is burnt out or loose in the socket, it should be replaced.

To eliminate doubts about the lamp's serviceability, proceed as follows: connect one conductor to the positive (+) and the other to the negative (-) pole of the battery, and connect the free ends of the conductors to the lamp. It does not matter how the conductors are connected to the lamp. One conductor to the current-supplying connector, and the other to the lamp body. If the lamp does not light, it should be replaced.

Note: Make sure that the contacts of the lamp and lamp socket are not rusted. If necessary, clean rusted or bent contacts and restore them to a perfect condition.

If the lamp is in good condition, insert the lamp and turn it on. If the lamp does not light, use a test lamp to check for supply voltage. To do this, connect the test lamp to ground. This means that one wire of the test lamp must be connected to a reliable ground of the engine (clean metal surface) or directly to the negative pole of the battery. The other electrode of the test lamp (+) must be connected either to the current-carrying plug or inserted into the current-carrying wire. If the test lamp now lights up, but the incandescent lamp still does not light, then there is a break in the ground wire. To check this, install a jumper from the ground to the lamp socket. The lamp should light up.

If the lamp's current-carrying conductor has no voltage, i.e. the control lamp does not light, it is very likely that the switch is faulty. Check the switch.

Otherwise, it is necessary to check the hanging module.

Checking Electric Motors

Increasingly, small electric motors are being used in cars to improve comfort. They are used in mechanisms such as window lifters, the drive for the sliding roof panel or the electric central locking system. Each electric motor is activated when needed by a switch, in most cases manually.

Check the fuse for the corresponding electric motor and replace the fuse if necessary.

Application: Electric motors of the window lift and the roof panel drive are usually equipped with a protection machine, which opens the electric circuit when overloaded, and closes it again after a while. Before switching on again, it is necessary to eliminate the cause of the overload. It may consist of frozen windows or dirty window guide rails.

If the fuse blows again immediately, a short circuit has occurred.

To definitely determine whether the electric motor is working properly, it is necessary to connect it with two auxiliary wires with a diameter of approximately 2 mm directly to the car battery or to the positive and negative connectors located in the engine compartment. The positive pole of the battery must be connected to the positive connector of the electric motor, and the negative pole to the negative connector. In doubtful cases, the location of the positive and negative connectors of the electric motor is determined in accordance with the electrical diagram. If necessary, the electric motor is removed. All electric motors of the car are supplied with an on-board voltage of 12 to 14 volts. If the electric motor now works normally, the cause of the malfunction was the lack of supply voltage.

Note: If the motor rotates slowly or intermittently, the carbon brushes may be worn out and should be replaced.

If the engine is running, use the electrical diagram to determine which conductor supplies voltage to it when the switch is pressed and before the ignition is turned on.

Check the supply wire with a test lamp. Since a large current flows through the electric motor, you can use a regular incandescent lamp as a test lamp. It is equipped with sharp electrodes that can be used to pierce the connecting wire. This allows you to easily determine the presence of supply voltage. Electric motor connectors are marked with unified numbers with small digits:

• terminal 32 is the ground connector (-);
• terminal 33 is the positive (+) connector.

Reversible electric motors, such as window motors, have two positive terminals. In such motors, terminal 33L is energized to make the motor rotor rotate to the left, and terminal 33R is energized to make the motor rotor rotate to the right.

Note: The windscreen wiper motor has a different terminal designation, see the relevant chapter.

If voltage is not supplied to the motor, the supply circuit is faulty. In accordance with the electrical circuit, find the fault in the wiring and fix it. Electric motors, due to the need for high currents, usually have an additional switching relay. Checking the relay is described in the relevant chapter.

If no fault was found, check the switch.

If there is a wire defect, it is advisable to lay a new wire, since it is quite difficult to localize the wire defect.