Checking the relay (Audi A6 C5)

Many electrical circuits have a relay in their structure. A switching relay works like a switch. For example, in order to turn on a consumer using a manual switch, you need to manually press it or move it to the desired position. In this case, the relay "receives an order" to supply power to the corresponding consumer. Of course, the voltage from the battery to the consumer could be supplied directly through the switch. But in the electrical circuit of all devices consuming a large current (horn, fog lights, radiator fan), a relay is included as an intermediate link in order not to overload the switch or to shorten the current path. Along with such switching relays, there are control relays, for example, for the interval mode of the windshield wiper and washer.

Checking switching relays

When the corresponding consumer is switched on, the voltage supplied to the relay closes its electric circuit. The magnetic coil inside the relay attracts the contact, thus closing the circuit of the "working" current. The "working" current flows from the relay to the consumer.

The easiest way to check the relay's functionality is to replace it with a known good relay. This is what workshops do. But since a car enthusiast does not always have spare relays at hand, the following approach is recommended when checking them.

1. Remove the relay from the holder.

2. Turn on the ignition and the corresponding switch.

3. First check with a voltage tester whether voltage is supplied to terminal 30 (+) on the relay holder. To do this, connect the tester to the "ground" (-), and carefully place the other contact rod on terminal 30 (+). If the tester's LED lights up, then there is voltage. If the tester does not register voltage, use the circuit diagram to find an open circuit from the positive pole of the battery to terminal 30 (+) of the relay holder.



4. Make a jumper from a piece of insulated wire, stripping the insulation from its ends.

5. Connect this jumper to terminal 30 (+) on the relay holder (voltage is supplied here constantly from the battery) with the closing contact of relay 87. This technique does almost the same thing that a working relay should do. The location of the terminals on the relay holder can be determined by the markings on the contacts or on the relay itself.
If the corresponding network consumer works when the jumper is connected, then we can assume that the relay is faulty.

If the consumer does not work in this case either, find out if the consumer's connection to the vehicle's "ground" (-) is working properly. Then, using the circuit diagram, find and eliminate the break in the circuit from terminal 87 of the relay to the current consumer.

6. Install a new relay if necessary.

Attention! If the relay functions intermittently, then the fault, as a rule, should be looked for in the relay itself. Sometimes the so-called gluing of the relay contact occurs, as a result of which it does not open, although the relay otherwise works perfectly. If this fault is detected, simply knock on the relay body. If such a relay short circuit occurs again, then replace this relay with a new one.

This article was previously published on the resource: AudiManual.ru