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Do-It-Yourself Projects
Isolating and Replacing Problematic Relays
By Mike Bumbeck/
Printable version
Degree of DifficultyModerate
Estimated Time180 minutes
180 minutes
Remove and Replace
While pulling out the multimeter and testing every relay under the hood, dash or carpets is one way to commence attack on mysterious electrical problems, a better way is to obtain a service manual and isolate the circuit in question by consulting a wiring diagram. First check and see if the connector has become corroded or clogged with road grime. A quick cleanup of the contacts may be the lucky fix. One of the easiest ways to test a relay, once the circuit and relay are isolated, is to swap it out with a duplicate that is known to be good and see if the circuit and relay work together once again.
Relays of the same voltage and amperage are often used throughout the vehicle, so just find one that has matching numbers and pin connectors, swap it out, and test away. When swapping out relays, make sure to only swap with replacements of the same voltage and amperage rating, and keep in mind that some relays may require a diode to complete the circuit.
A service manual can help determine the correct replacement relay, as can a qualified parts counterperson. An electric radiator fan that doesn't switch on when an engine gets hot can lead to overheating, which could, in turn, lead to a blown head gasket or cracked cylinder head—an expensive mess caused by the failure of an inexpensive part. The failure of a five-dollar part can cause the five hundred dollar problem, so swapping out the relay in question with a new one may be the best plan of action.
Step 1 - Disconnect the negative post of the battery before working on the electrical system.
First Disconnect the Battery's Negative Post
Step 2 - Isolate the problem circuit and find the relay in question. This cluster is home to six relays that control everything from the AC condenser fan operation to the compressor magnetic clutch activation.
Find the Problem Circuit and Relay
Step 3 - Remove the screw or fastener holding down the relay. Release connector tabs. Disconnect the relay from the connector by grasping the relay and connector itself. Never pull on wires to remove a connector.
Disconnect the Relay From the Connector After Removing Screws or Fasteners
Step 4 - Check the connector pins for corrosion or road crud. Problems can sometimes be cured with a cleaning.
Check the Connector Pins for Corrosion or Road Crud
Step 5 - A dab of dielectric grease can help prevent corrosion from recurring, and keep moisture out of the connector.
Dielectric Grease Can Help Prevent Corrosion from Recurring
Step 6 - Reconnect the relay and secure the fastener. Check that all wiring is as it was before reconnecting the battery.
Reconnect the Relay and Secure the Fastener
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