Checking the relay (VW Polo 4)

Many electrical circuits have a built-in relay. The switching relay works as a switch. When the consumer of electricity is switched on manually through the switch, the relay receives a command to supply current to the consumer. Of course, it would be possible to supply current to the consumer directly through the switch from the storage battery. However, all consumers that require a large current have an intermediate relay switched on so as not to overload the switch and to protect the circuit from a short circuit.

Checking the switching relay

Current is supplied to the relay when the corresponding consumer is switched on. Due to the switching current, the electromagnet coil inside the relay attracts the contact and thus closes the electric circuit of the working current. The working current then flows through the relay to the consumer.

The easiest way to check the relay's functionality is to replace it with a working one. This is what they do at service stations. Since a car enthusiast only very rarely has a new relay at his disposal, the following sequence of operations is recommended:

• Remove the relay from the board.
• Turn on the ignition and the corresponding switch.
• First, use a voltage tester to determine whether voltage is being supplied to the positive terminal (+) of the relay board. To do this, connect one electrode of the tester to ground (-), and carefully insert the other electrode with the sharp end into the terminal. If the LED of the tester lights up, then voltage is being supplied. If the tester shows no voltage, use the electrical diagram to find a break in the circuit from the positive pole (+) of the battery to the terminal.
• Make a jumper from a piece of insulated wire, cleaning the ends of the jumper until shiny.
• Connect the positive terminal (+) of the relay board using this jumper (this terminal is always supplied with voltage from the positive pole of the battery) with a terminal at the relay output.

This operation does practically the same thing as a working relay. The location of the relay board terminals can be determined by the color of the wires or by using the electrical diagram.



If, for example, the high beam lights up when the jumper is installed, we can conclude that the relay is faulty.

If the high beam does not light, you need to find out if the headlights are connected to ground (-) properly. Then, using the electrical diagram, find and fix the break in the wiring from the relay terminal to the main headlights.

If necessary, install a new relay.

Note: If a fault in the electrical circuit with a relay occurs only from time to time, the cause is usually due to a defect in the relay. In this case, the relay contact remains closed or open, while the relay functions perfectly the rest of the time. If this type of fault occurs, lightly tap the relay housing. If the relay operates as a result, it should be replaced.