Relays

Relays are used to supply electrical current to the components of some vehicle electrical accessories. A malfunctioning relay causes failure of the component it serves.

If a relay is suspected of being faulty, it must be removed and diagnosed at a dealership or a specialized repair shop. A faulty relay is replaced as an assembly.

Relay Testing

Many electrical circuits include relays. When a consumer is switched on manually, the relay receives a command to supply power to the consumer. Power can also be supplied directly to the consumer from the battery. When high currents are consumed, a relay is included in the circuit so as not to overload the switch. In addition to switching relays, there are also function relays, for example the windshield wiper/washer relay.

Switching Relay Testing

When the corresponding consumer is switched on, a signal is sent to the relay. The control current energizes the electromagnetic coil, which closes the operating current circuit and supplies power to the consumer.

The easiest way to check a relay is to replace it with a known good one, as is done at service stations. If a spare relay is not available, it is recommended to test as follows. The terminal designations below may differ from those on your relay.

TEST

1. Remove the relay from the relay holder.
2. Turn the ignition and the corresponding switch on.
3. Using a voltmeter, check whether there is voltage at terminal 30(+) of the relay holder. To do this, connect the meter to ground (-) and carefully insert the other probe into terminal 30. If the meter LED lights up, voltage is present. If the meter shows no voltage, check the wiring diagram for an open circuit between the positive (+) battery terminal and terminal 30.
4. Prepare a jumper wire from insulated wire with stripped ends.
5. Connect terminal 30 in the relay holder (+ battery, always live) to the normally open relay contact output (terminal 87) with the jumper. This simulates the operation of a good relay. The terminal locations in the relay holder are indicated on the relay.
6. If the consumer operates with the jumper connected, the relay is faulty.
7. If the consumer does not operate, check that the ground connection to the consumer is good. Then check the connection from terminal 87 to the consumer. If an open circuit is found, repair it.
8. If necessary, install a new relay.

* If the fault appears intermittently, the relay is usually the cause. In this case the contacts may be stuck together. Lightly tap the relay housing with your finger. If the relay then operates, replace it.