Electric radiator cooling
fans use a lot of juice. So carmakers use a fan relay to switch them on and
off. If your radiator fan doesn't work, don't automatically assume you've got a
bum fan motor. First test the fuse for the radiator fan. If it checks out, test
the radiator fan relay.
Here's how. Unplug the
electrical connectors to the radiator fans. Then turn your A/C to the MAX
position and start the engine. Use a multimeter to check for power at the
unplugged fan connectors. If you don't see 12 volts at the connectors, the fan
isn't getting power from the relay. The relay is usually located near the
bottom of the engine compartment on a metal frame member. The metal acts as a
heat sink to keep the relay cool. So, unplug the connector at the relay and
repeat the check for power. If you get power, you've got a bum relay. If you
aren't getting power at the relay, you've got a more serious wiring or computer
problem, and that's a job for a pro. But you can easily replace a bum relay
Start by removing the old
relay and checking for corrosion around the mounting surface. DIYers often just
replace the relay without removing the corrosion. That's a prescription for a
repeat failure. Instead, sand off all the corrosion until you get to bare
metal. Then apply a generous amount of thermal grease to the back of the new
relay (see photo, right).
Secure it to the metal frame and let the grease squish out
on all sides. The new relay will power up the fans, and the thermal grease will
transfer heat to the metal frame and prevent corrosion.
— Rick Muscoplat, Automotive
For more vehicle maintenance and repair tips, visit our Auto Repair section.