Switching relay (Audi A4 B5)

Function of switching relay

1. When a certain consumer is switched on in the switching relay, the "switching current" supplied to terminal 86 closes the electrical circuit to terminal 85 (ground).

2. As a result, the electromagnetic coil attracts a powerful contact, counteracting the pressure of the spring, and thus closes the electrical circuit for the passage of the "working current".

3. In order to avoid voltage drop, the operating current is supplied via a short path to terminal 30 of the relay and from there, with the switch contacts closed, through terminal 87 further to the consumer.

4. Sometimes there is another terminal 87a. It is closely related to terminal 87, i.e. it has the same function.

Troubleshooting a Switching Relay

1. There should always be voltage at terminal 30 (supply voltage to working contact).

2. To check the voltage supply, remove the relay and tap the test lamp needle on terminal 30 in the relay base. No current: defect in the supply wire.

3. If the corresponding switch is on, there should be voltage at terminal 86, (applying voltage to the relay coil).

4. To check, tap terminal 86 in the relay base with the needle of a test lamp.

5. No current: defect in the wire or in the switch.

6. Terminal 85 is the ground wire to the coil. Check the battery with a test lamp –+ (for example, terminal 30).

7. The relay coil is checked on the removed relay: connect terminal 86 to the battery positive and terminal 85 to ground. The electromagnetic coil should attract the relay contact with a distinct sound, otherwise the relay is defective.

Temporary help for a faulty switching relay

1. Remove the relay from the socket.

2. Short-circuit terminal 30 and 87 in the relay socket with a paper clip or a piece of wire. This will provide the corresponding consumer with direct current.

3. To turn it off, disconnect the short-circuit jumper, since in this case this consumer is shorted.