PCM Outputs - High or Low?

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May 15, 2006 | 04:40 PM

Happy Jim

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From: Wokingham, United Kingdom

PCM Outputs - High or Low?

Hi all,

I'm just finishing up my home made loom and a thought occurs

Does the PCM signal a change in state as +12V or Earth?

Only critical on Fan1 - Fan2 & Fuel pump, as I'll be pushing these through relays.

Thanks

Jim

May 15, 2006 | 05:08 PM

Schitzo

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From: Minneapolis MN

for the fuel pump 12v for the fans ground (earth)

May 15, 2006 | 05:08 PM

70 LS1

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From: Gig Harbor, Wa

Depends on the function. Some are active high and some are low. For the fans the PCM grounds the 3 relays turning them on.

Don't know on the fuel pump.

May 15, 2006 | 05:09 PM

70 LS1

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Damn, beat me to it.

May 15, 2006 | 07:42 PM

ghettocruiser

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On a related note... About those fan relays. Im curious because Im working on the same thing right now... Why are there three relays for the fans??? There are only two cooling fans, but three relays. Also...in the pin outs that I have for a 99...they mention Fan High Output... Fan Low Output... What is the high/low they are referring to?? Thanks...

Justin

May 15, 2006 | 07:53 PM

70 LS1

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Check out the schematic. When the Fan Low Output goes low it will energize the two fans in series so each fan only gets 6V. This will make the fans run in slow speed. When both the Fan Low Output and Fan High Output go low, they will energize the fans in parallel with each fan getting 12V.

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May 15, 2006 | 08:32 PM

88s10

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From: seaford D.E

fuel pump is 12v fans are ground and mil light is ground signaled from pcm. hope that helps

scott

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May 16, 2006 | 07:49 AM

ghettocruiser

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From: West Chester, PA

Hmm..ok. That makes sense.. So on an LS1 car, at a certain temp, both fans come on at 6V rotating at a slow speed. Then when the temp rises to another point, they both get full 12V and rotate at full speed. Is this basically correct? So when I wire this up...I should wire it the same way as stock...and both fans will always operate together?>?

I was under the impression that I should be running off of one fan at full speed, then at a certain temp have the second fan come on..or with the A/C...

Thanks for the drawing and the info!!

Justin

May 16, 2006 | 08:09 AM

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Schitzo

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From: Minneapolis MN

Quote:

Originally Posted by ghettocruiser

I was under the impression that I should be running off of one fan at full speed, then at a certain temp have the second fan come on..or with the A/C...

Thanks for the drawing and the info!!

Justin

this is how I will be running my fans. It is a simple setup and works just fine

May 16, 2006 | 10:10 AM

#11

70 LS1

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From: Gig Harbor, Wa

Quote:

Originally Posted by Schitzo

It is a simple setup and works just fine

So does the stock setup with 3 relays. its only one more relay and is completely controlled by the PCM.

May 16, 2006 | 02:57 PM

#12

Schitzo

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From: Minneapolis MN

now that I have looked at it closer, I think the stock setup is better since both the fans are always running. The schematics were alittle bit confusing at first but now I get it..