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Old 05-03-2013, 05:14 PM
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cooling fan runs more than it should... possible relay issue?

Hi, I am troubleshooting a cooling fan issue on my 1995 Japanese-made Toyota Corolla. When it's cold and I turn the key to ON, the fan does not cut off as designed. Also, the fan has begun to run too often while driving. Sometimes it cuts off after a period of cooling when the engine is hot, but more often than not, it stays on.

When I turn the car off, the fan cuts off, as it should.

The ECT switch is new, aftermarket. I cleaned the connections to the ECT switch and to the relay with electrical contact cleaner, but the problem persists. The relay is a Nippondenso-type Toyota 90987-03003/156700-0130 12V 4Pin light relay.

Deciding to test the relay, I referenced my manuals. All of them - Chilton, Haynes and Toyota - say that when I test the relay posts with an ohmmeter, I should get "continuity." The question is, I don't know if "continuity" in the manuals' interpretation means zero resistance, or anything less than infinite. When I test pins 1 and 2, I get 0 ohms resistance. But when I test pins 3 and 4, I get about 71 ohms. Is this normal, or have I diagnosed a bad relay? Would resistance across these two pins cause the fan to stay on more than normal?

Putting voltage across pins 1 and 2 resulted in a clicking sound and no continuity between posts 3 and 4, which is correct behavior, according to the manuals.

Thanks for any help in advance.

-Paul

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Old 05-03-2013, 05:39 PM
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Sounds like the radiator is not throwing the heat from the engine , causing the fan to run longer as it doesnt cool the engine well. Just a thought.
After you warm it up, shut the engine down and feel the radiator from top to bottom. See if it is warm all over or if it has a bunch of cool spots.That will tell all.
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Old 05-03-2013, 09:55 PM
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Thanks, but this doesn't account for why the fan isn't shutting off when the engine is cold and first started.

My original question was if the relay should be showing ~70 ohm resistance across pins 3 and 4.

I tested the ECT switch a few months ago and it was fine.

-Paul
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Old 05-03-2013, 10:22 PM
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Also, the radiator is very clean inside and functioning well, no blockages. I removed it and flushed it multiple times last summer and filled it with clean fluid and distilled water. It's still bright green and barely lost a drop since then. I keep the overflow tank topped off. I get good cooling, drove it over a thousand miles last months and never went above normal temperature. Drove it a thousand a few months before that and same thing. Brand new thermostat. I'm thinking there might be a short at this point, but not sure how to troubleshoot.
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Old 05-03-2013, 11:02 PM
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E=ir

When using a meter and testing for resistance some basic electrical knowledge is required.
Continuity means a complete circuit.
This is also known as '0' electrical resistance. Meaning an electrical circuit can flow freely through the circuit without resistance.

But the opposite of this is infinity, meaning there is an infinite amount of electrical resistance. Meaning an electrical circuit cannot flow through this.



vicrod
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Old 05-03-2013, 11:51 PM
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unplug the coolant temp sender and see if it stops?
if it does it can be the sender or a short in that wiring..

ecu could turn fan on if it gets no signal from sender..
not sure on a toyota of those years..
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Old 05-04-2013, 07:28 AM
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From your description you have a bad relay. I have never seen a 4 terminal Normally Closed (NC) relay, not saying they don't exist-just I've never encountered one.

From your description this is what I'm getting
Terminals 1-2 are the coil terminals, you stated you put voltage across them and the relay clicked. You didn't get continuity across these two....... If these are the coil terminals you should get continuity.

3-4 terminals from your description, would be NC, as you stated you have continuity and a measurment of 71 ohms, when the relay isn't energized. (which I've hever encounted).

in most instances that I'm fam with, the switching side of a 4 pin relay is NO, or the contacts are open untill the relay is energized, ie...... the temp switch gets hot and closes, sends juice to the fan relay, it closes sending juice to the fans etc......

Not sure how a NC relay would work in a cooling set up, or I'm not understanding you description
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Old 05-04-2013, 03:29 PM
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The problem with troubleshooting Toyota systems is sometimes the translation ends up being Engrish instead of English, leading to some confusion. They usually specify continuity on a meter reading, even if it's 0 ohms or a small resistance. The relay you tested should have had 70 ohms on the 1 and 2 terminals. This is the standard resistance for small Toyota relay coils. The fact that the relay is normally closed with power off is standard with many Toyota cooling fans. This is done in case there is a failure of the fan control module or some other part of the system, the relay will go to the off position and the fan will come on, making the system "fail safe". There may be several relays controlling the fan and you may have to backprobe the terminals for voltage readings to see which part of the system is causing the problem.
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Old 05-04-2013, 03:56 PM
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Quote:
Originally Posted by EOD Guy View Post
3-4 terminals from your description, would be NC, as you stated you have continuity and a measurment of 71 ohms, when the relay isn't energized. (which I've hever encounted).
I'm sorry, in my original post I incorrectly stated that terminals 3-4 were getting 71 ohms resistance. It's terminals 1 and 2 that are giving this resistance. When the relay is not energized, terminals 3 and 4 give zero resistance (continuity, which the manual says is correct). When the relay is energized (across terminals 1 and 2) I am getting infinite resistance (no continuity) across terminals 3-4, which the manuals also say is correct. It's the 71 ohms resistance across terminals 1 and 2 that I'm wondering about. A previous poster, vicrod, says that 71 ohms is not the same as "continuity." He says that there should be zero resistance to meet the definition of continuity. Of course, none of my three manuals makes this clear. I'm supposed to just know it, I guess. For what it's worth, Wikipedia describes an open circuit as one with "excessive" resistance. This is the definition that I always assumed... which is that a circuit with some resistance but which current can flow through is still technically a closed circuit, and therefore continuous.

Thanks for all the help guys. I am listening to what everyone says, but I wanted to clear up the error in my original post.
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Old 05-04-2013, 04:06 PM
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Quote:
Originally Posted by sparkchaser View Post
The relay you tested should have had 70 ohms on the 1 and 2 terminals. This is the standard resistance for small Toyota relay coils.
Okay, it's reassuring to hear someone say that. I just clarified this with EOD Guy... yes, I get 71 ohms resistance across terminals 1 and 2. In my original post I incorrectly said I got this resistance across terminals 3 and 4.

Anyway, then, I suppose my relay is fine. I understand the failsafe concept... better to have the fan always running than never running. On the other hand, I have to figure out what is causing the incorrect fan operation. Time to backprobe, I guess. I will let everyone know what I find. I am going to follow gearheadslife's suggestion by disconnecting the ECT switch to see how the fan reacts.
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Old 05-04-2013, 05:19 PM
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A 4 pin normally closed relay isnt too common but they are out there. I would assume they are used for like a Wide open throttle cutout for an AC clutch etc.
If you have an EWD for the cooling fan circuit that would be a huge help.
Also wait till you get to the EWD and wire colors. There is a translater for wire colors too. B is not for blue , L is for blue and it goes on.
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Old 05-05-2013, 06:07 AM
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OK I understand the failsafe idea....... That being the case something has got to trigger the relay when the engine is cold and my guess would be the temp controller. Again a guess is that the temp controller controls the fan relay directly or via a second relay.
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Old 05-05-2013, 06:23 AM
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I don't know how the Toyota manual is worded, but there is a difference between continuity and resistance.
Continuity - is there a connecting path between two points. The path you are checking must be disconnected from other wiring or you will not get an accurate measurement. You can use simple a test lamp or the resistance scale on a VOM (voltage-ohm-millammeter) instrument to verify continuity.
Resistance/ohms - measure the resistance between two points (which must also have continuity). This measurement also assumes there is zero voltage from other sources (e.g., your car) because the VOM runs its own voltage through the path to measure resistance.

Bruce
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