Relay — purpose and replacement (BMW 7 Series E38)

To supply power or control signal to some of the electrical consumers in the vehicle (such as fuel injection system components, horn, starter, cooling fan, fog lights and others) relays are used. In fact, the relay is an electric key that ensures the closure of the high-voltage circuit by a low-voltage signal. If the relay fails, the corresponding consumer will not function. The relays are installed in the mounting block under the instrument panel and in the blocks in the engine compartment (see Specifications in Chapter On-board electrical equipment). A description of how to check the proper functioning of the relay is given below. Failed relays are subject to replacement.

If it is not possible to find out how to connect the relay to the corresponding electrical circuit using the electrical connection diagrams (Electrical equipment diagrams), it should be remembered that the approach to testing any relay is, in principle, the same in all cases.

In most cases, the control circuit is always connected to two of the relay contact terminals. When low-voltage voltage is applied to these terminals, current begins to circulate through the relay control winding, resulting in the closure of the large contacts of the working circuit of the consumer of electrical energy. The remaining terminals are the terminals of the working (H/H) circuit.

To facilitate identification of the relay terminals, explanatory markings with an image of the key connection diagram are usually applied to its body.

1. Before removing the relay, make sure that the corresponding circuit is de-energized.



2. Connect a fused jumper wire between one of the relay control terminals and the positive battery terminal. Use a second jumper wire to ground the other control terminal – the relay should click. Some relays require polarity – if there is no click, try reversing the polarity of the control terminals.

3. With the jumper wires connected, check for continuity between the I/O circuit terminals.

4. If the test result is negative, replace the relay.

This publication was borrowed from an online resource: «BMWman.ru»