Troubleshooting fan relay - JeepForum.com

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post #1 of 19 Old 06-08-2013, 04:09 PM Thread Starter
tommyd123
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Troubleshooting fan relay

The electrical fan in my 2002 was not working. I know the fan is good, so now I am at the relay. What voltage readings should I be getting at the connection to the relay and to the fan. Also, is the relay interchangeable with any other Chrysler vehicles?

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post #2 of 19 Old 06-09-2013, 04:17 AM
4Tom
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The relay is a solid state electronic relay under the headlight. Not sure if it was used in anyother models but I doubt it was.

Its very difficult to test because the output to fan isn't a constant voltage you can read with a meter. It uses pulse width modulation or PWM for short. Easy way to think of it is short pluse of 12v sent to fan.
The wider the pulse the faster the fan will spin. But a DC meter can't read pluses.

Many test the fan by applying 12v dirrectly to fan. Its not a conclusive test by any means as the fan may spin but doesn't tell you if the fan is drawning too much current.

The electric fan relay can and does just fail, it can also fail if the fan is drawing too much current. Repeated relay failure is often down to bad fan ( or cheap replacement relays)

I would start with replacing the relay and see how you get on.

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post #3 of 19 Old 06-09-2013, 05:50 AM Thread Starter
tommyd123
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4Tom, thanks for the reply.

I'll keep my eyes open at the local junkyard for a relay. I would really hate to spend 50 dollars on a new one just to have it go bad by my fan pulling too much current.
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post #4 of 19 Old 06-09-2013, 05:55 AM
Terminal
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I had to replace mine too a several years ago. Why get an old junkyard one that will have the same issue very soon and go through the trouble of replacing it again? It would be wise to buy the new and not fool with installing another. It's a real pain in the @ss to replace the fan relay. To each his own I guess...
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post #5 of 19 Old 06-09-2013, 06:40 AM Thread Starter
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I understand your reasoning to go with a new part, and appreciate your advice. I have been living without a radiator fan for over a year now and I drive the jeep very little, so I think a junkyard relay will do fine.. Besides, if it keeps going out, then I know to look at getting a new fan.

As far as being a PITA to replace, it takes me no more than 5 min from start to finish and a single 8 or 9mm socket.
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post #6 of 19 Old 06-09-2013, 06:45 AM
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How's that cooked transmission fluid that runs through the radiator looking?

Good luck to you.
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post #7 of 19 Old 06-09-2013, 06:56 AM Thread Starter
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Considering it is NOT cooked, not too bad. Thanks for asking.
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post #8 of 19 Old 06-09-2013, 07:39 AM
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I'm guessing you have a mechanical fan as well? I bought a Mopar fan relay about five years ago and it's been fine since. Like 4Tom said, not that easy to diagnose, but it can be done. But with such a cheap part, might as well just replace it.
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post #9 of 19 Old 06-09-2013, 01:35 PM
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The input voltage will be 12 volt, plus a 5v PWM signal from the PCM. It pulses the relay, which in turn will pulse the output. You cannot read an accurate voltage on the output of these.

Getting a used one, you'll run into the same issue quickly.

What I'd recommend: getting a new one at a local parts store that comes with a lifetime warranty. Use some type of thermal compound (CPU compound like used on computers is best) to put under it before you remount it. IF it fails again, you know your fan is pulling too much current and needs a replacement as well. Swap out the lifetime warranty relay, and replace the fan as well at that time.
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post #10 of 19 Old 06-10-2013, 08:08 AM Thread Starter
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Thanks for the feedback, everyone. More than likely I will be getting the new fan relay.
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post #11 of 19 Old 06-10-2013, 08:43 AM
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I've got a handful (7) that I have on hand. Replaced one with a virtually new one and haven't had an issue with it since.. My problem I recently had was the connector on the fan having corrosion issues. The mechanic I see has a DRBIII scanner which we used to diagnosed the fan and relay. One of the relays I had was toast, fan is good. Once we got the connector fixed, all was good again. Also with the relay I did have in originally when it went, it would throw an engine code as well.

The beatings will continue until attitudes improve!

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post #12 of 19 Old 06-10-2013, 10:03 AM
Cirruslydakota
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Quote:
Originally Posted by narnwv View Post
The input voltage will be 12 volt, plus a 5v PWM signal from the PCM. It pulses the relay, which in turn will pulse the output. You cannot read an accurate voltage on the output of these.

Getting a used one, you'll run into the same issue quickly.

What I'd recommend: getting a new one at a local parts store that comes with a lifetime warranty. Use some type of thermal compound (CPU compound like used on computers is best) to put under it before you remount it. IF it fails again, you know your fan is pulling too much current and needs a replacement as well. Swap out the lifetime warranty relay, and replace the fan as well at that time.
^This.

Its exactly what I did and I havent had any problems at all. I also replaced the fan motor at the same time. I also have the mechanical fan but the electric is needed for good A/C performance. When I do junk yard runs I usually grab the fan relays if theyre easy to get to. I have 5 laying around here (I keep 1 in my tool bag with some thermaltake cpu mount) for those "just in case" moments.

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post #13 of 19 Old 06-15-2013, 02:34 PM Thread Starter
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Update...


Replaced the relay with a junkyard one and works good, for now. Considering the price I was charged, I feel good about the used part.

I originally asked if the fan relay was interchangeable with other vehicles, and I found out it is. I pulled mine from a minivan. I forget if it was a dodge, chrystler, or Plymouth, but it worked just fine.

As an added bonus, I pulled some headlights from the junkyard jeep. Now it looks like I have brand new headlights now! I'll call this a good day!
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post #14 of 19 Old 06-15-2013, 04:45 PM
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That relay for the radiator fan is used on other vehicles as well. Many of the vehicles Chrysler built that year..
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post #15 of 19 Old 06-15-2013, 06:06 PM
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I can't justify buying a new one when I have a handful of virtually new ones at my disposal now. So it blows. Just change it out and keep going. Got another one yesterday. Some one obviously cut the bottom of the header panel to replace it. Looks to be a matter of months old. Same as the one I put in to replace my bad one. Up here to get from the dealer is always at least twice for you guys are able to get them for. Why give more money to a dealership when there's plenty of good ones that will be usually scraped anyways.

The beatings will continue until attitudes improve!

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