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: How to check for bad relays in fuse box?


Communicator7
07-16-2005, 06:40 PM
Hey guys,

A few days ago I checked in the fuse box of the engine bay & found a blown fuse to a radiator fan. There was some suggestions to check the relays.

Well I'm wondering how do I go about checking to see if the relays in the fuse box are good or bad? I'm glad I asked this because this would be some useful information for me to carry down the road whenever I might have a possible problem with my car. Thanks!

ESMIKE96
07-16-2005, 09:53 PM
Basicly.

If your fans arnt working. And you think its a relay. Switch the fan relay with anouther relay thats in the same area as the fan relay. If your fans kick on then it was the relay. If they dont its not the relay.

Im sorry I cant be more of a help but its the only way I know how to check them.

froggy81500
07-17-2005, 12:23 AM
You have to figure out which are the two terminals for the field coil. Then you need to connect 12 volts to the positive and ground the negative and you will hear a "click" and might even feel it. Peppa boy's idea will work if you swap relays with something that you can turn on and off like the wipers (if they're the same relay) and you'll now for sure if the relay is bad or not. My instructions are just in general for any relay but for the car, try what peppa suggests.

lextrep
07-17-2005, 12:53 AM
The easiest way to check the relay is to do as Peppa Boy suggested and swap it with a known good relay. If you want to electrically check them the 2 outer parallell pins in the row that has 3 pins are the coil,(#85is negative and 86 is positive if they are numbered ) put 12volts to them and you should hear the relay click or check the other 3 pins with ohmmeter they are a common, normally closed and normally open

'98-ESer
07-17-2005, 01:07 AM
I just replaced the high and hi/low relays.

They cost $6 each.

Communicator7
07-17-2005, 04:48 AM
Hmm, good ideas. I'll switch them out & see how it goes. 98-Eser, I wonder why made your hi/low relay went bad?

alarkyokie
07-18-2005, 08:35 AM
If the need comes up to check a relay further, (and you have a meter),apply 12v as
stated above. Connect ohm meter across the other contacts and verify that the
contacts are electrically closing. Remove the 12v and the contacts should open.
There may be "normally open"(NO) contacts, and "normally closed"(NC) contacts,
which describes the no power applied state.

'98-ESer
07-18-2005, 09:49 AM
I only brought up the relays because of their low price. You can spend all day (or more) chasing down electrical problems or 'invest' in a 6 dollar part.

If you suspect a relay of being bad, you have to consider that it may only be failing under the heat/cold extremes *or* engine vibration *or* a combination thereof. Simply testing them for how they react to 12 volts on a workbench won't tell you if you the relay is good or not. It just tells you that it works ok on the bench.

Sometimes it pays just to replace the cheap parts. Those relays get a constant workout in the harsh under-hood environment.