# Can someone explain a 3 pin relay to me?



## DKWunlimited (Sep 11, 2006)

I need help understanding what a 3 pin relay does. I know that it is in the fuse box however I have one person (a car saleman) telling me that it is no big deal, that it's just like a fuse but has 3 pins instead of 2. I have another person telling me that it is a relay switch that relays any problems with the car to the computer and makes the warning lights come on and it's a HUGE deal because if it is missing it can make a car look like it is fine when it is not.

In laymans terms.. what does a 3 pin relay actually do? and would you buy a car if it was missing?


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## unioncreek (Jun 18, 2002)

To me a relay is used to turn something on, most often they are used on lights so the lights get a full 12 volts. Have you Googled it?

Here Debbie, I Googled it. I was curious too.
http://www.autoshop101.com/forms/hweb2.pdf

Bob


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## DKWunlimited (Sep 11, 2006)

Yes, I have googled it but what I seem to be finding is technical jargon so I was hoping someone could explain it better.


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## unioncreek (Jun 18, 2002)

Debbie,

I would ask the salesman which relay is missing and why. Also ask them to replace it, it's just like putting a new fuse in. If they balk at doing it I would be cautious, you may want to make an appointment with a mechanic so you could get an independent assessment of the vehicle.

Bob


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## DKWunlimited (Sep 11, 2006)

I have done both of those things.. the salesman is saying that it just controls the dash lights and is "no big deal" he doesn't have one is stock so he wants me to go ahead a buy the car and they will replace it when the part comes in. The mechanic is saying no way no how, he says that the relay is what sends the signals to make the warning lights on the dash show a problem and the fact that it is missing is a bad sign.. he says people often pull these relays before they trade in or sell a car to avoid those lights coming on.


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## cfabe (Feb 27, 2005)

I've not heard of a relay being used to turn on warning lights. Usually they are used to switch on the power to a high current device, like the headlights, defroster, horn, fuel pump, things like that. 

It's possible that the missing relay was never there in this car if it was a provision for an option that the car did not have. For example, in a car that did not come with a rear window defroster, there may be a spot in the fusebox for the relay that would power it, but the relay would have never been installed because it was not needed. They do this so they only have to produce one fusebox not a bunch of different ones.

If everything in the car is operational it may not be a problem. Like your mechanic has said, it could also be disabling something that was broken. If you can post the make/model/year of the vehicle and which relay is missing, I might be able to look up more specifc information on it.


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## DKWunlimited (Sep 11, 2006)

It's a 2001 dodge stratus.. I don't know the exact relay,, but when I took it in to O'rileys they said that it was a relay for the "body computer" and had to be purchased thru a dodge dealer. does that help?


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## OntarioMan (Feb 11, 2007)

If the relay is not such a big deal, wait for it to be replaced before you commit to purchasing. A relay controls something, and without that relay, that something will not work. As others have mentioned, just because there is a spot for the relay does not mean that the car requires that relay.

A 2001 vehicle is OBDII - which means it uses a computer to monitor and control many function of the engine/vehicle. Bring the car to a mechanic and get them to scan the computer for any error codes. A bit of a warning here is that codes can be reset, and may not return for weeks.

Purchasing any used vehicle is always somewhat of a gamble - even if you do research, purchase carfax or other reports, have mechanics inspect the vehicle, ect. ect. All this does is decrease the chances of you purchasing a lemon - but the chance is still there.


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## OntarioMan (Feb 11, 2007)

And you may be referring to the BCM - Body Control Module

A quick google search show : The BCM provides the following features:

â¢ Automatic door locks 
â¢ Battery protection 
â¢ Chimes 
â¢ Compass/mini-trip support 
â¢ Courtesy lamps 
â¢ BCM diagnostic support 
â¢ Door lock inhibit 
â¢ Headlamp time delay 
â¢ Ignition key lamp 
â¢ Illuminated entry 
â¢ Instrument panel dimming 
â¢ Mechanical instrument cluster support 
â¢ Power door locks (with/without remote keyless entry) 
â¢ Sliding door memory lock 
â¢ Vehicle Theft Security system (VTSS) 
â¢ Windshield wipers / washers (front and rear) 

I'll guess that its not the BCM relay, but a relay which controls something else, like power door locks, headlamps, wipers... something. Without the BCM, none of the functions above would work - so test them : do the door locks work, windshield wipers...


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## agmantoo (May 23, 2003)

It is probably that d***mn buzzer relay that annoys me to no end when I want to open the door with the key still in the ignition. I think it allows the computer to send an audible signal when something insignificant malfunctions or needs to be brought to the attention of a driver. The relay is probably somewhere in the vehicle where the previous owner put it when he removed the annoyance.


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## Wis Bang (Feb 20, 2009)

Relays use a low amperage circuit [like from the horn button] to turn on a high amperage device that is connected directly to full battery amperage. Keeps from melting down the dash & wiring harness if there is a short.


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## Ozarka (Apr 15, 2007)

close but not there. A relay is a tiny electromagnet which is a coil of wire wrapped around a piece of steel, energising the coil causes a piece of steel connected mechanically to a set of contacts to move, changing the contacts from open to closed or vicea versa. Since the specific application is not known, as a person who has been skinned by used car salespeople, if it's such an insignificant item, let them get it in, install it and see if the car still works. Listen to the mechanics and if they say put 'er in tha rearview mirror, walk away from the car.


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## agmantoo (May 23, 2003)

Ozarka you are close but still not there either
We now have two types of relays, electomechanical and solid state. We do not know the type that is missing do we?

A solid state relay (SSR) is an electronic switch, which, unlike an electromechanical relay, contains no moving parts. The types of SSR are photo-coupled SSR, transformer-coupled SSR, and hybrid SSR. A photo-coupled SSR is controlled by a low voltage signal which is isolated optically from the load. The control signal in a photo-coupled SSR typically energizes an LED which activates a photo-sensitive diode. The diode turns on a back-to-back thyristor, silicon controlled rectifier, or MOSFET transistor to switch the load.


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## foxtrapper (Dec 23, 2003)

I don't know what this "3-pin relay" is either. Where is this thing missing from, and how did you determine it was missing?

There is no one relay in the proverbial system that sends the codes to "the computer" like your mechanic has described. Quite honestly, as another mechanic, I'd say that mechanic isn't particularly competent if he's saying this. But I'm also quite well aware that I'm getting everything via hearsay, and not hearing his/her words or seeing the car.

A 2001 Dodge Stratus is not a remarkable or wonderful or rare car. You seem hesitant, so hesitate. If the car sells before this problem is fixed, so be it. There will be others on the market, as well other cars that are fine right now on the market. Unless there is some odd pressing reason that you absolutely must by this particular car right now, I would recommend erring on the side of caution.


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## Beeman (Dec 29, 2002)

DKWunlimited said:


> I have done both of those things.. the salesman is saying that it just controls the dash lights and is "no big deal" he doesn't have one is stock so he wants me to go ahead a buy the car and they will replace it when the part comes in. The mechanic is saying no way no how, he says that the relay is what sends the signals to make the warning lights on the dash show a problem and the fact that it is missing is a bad sign.. he says people often pull these relays before they trade in or sell a car to avoid those lights coming on.


 Let's start at the very beginning..

What if anything is wrong or not working on this car? What if anything brought your attention to this relay?


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## raymilosh (Jan 12, 2005)

I'm interested to hear your answers to beeman's questions.

Hearing what ive heard, though, I'm also thinking it may be a relay that made noise. I remove them onmy cars and others ask me to do it for them, too. It's the chime or buzzer that alerts me/annoys me while i have the door open or the keys in the ignition or the lights on, etc.

Listen for such a chime under those circumstances to see if the car is more silent than you'd expect it to be.


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## Ozarka (Apr 15, 2007)

agmantoo, the technical world just gets getting more and more complicated. I think that it is over complicated in many respects. I was studying a garage door opener today and counted 5 or 6 integrated circuits alone and I wonder just how many decisions does a gdo have to make? thanks for the update on solid state relays, there are so many more devices on the market than when I studied electronics and entered the electrical trade in '70. I think, more and more, I'd just rather beat on iron, but these nice nice folks keep askin' me to wire up their kitchen remodels.


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## cfabe (Feb 27, 2005)

Ozarka, back in '70, any guy with a little bit of electronics knowledge could build up a universal opener and drive down the street opening garage doors. That's not possible any more thanks to all those mysterous microchips in your shiny new opener that make an unhackable scrambled code. Sometimes complicated electronics are a good thing!


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