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Pcm Pin 33 And 42


bssfan
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Hello,

 

Trying to do an electric fan conversion. I have read that pre-2007 trucks (assuming 2007+ use variable fan speed control) have two output pins (pin 33 and 42) that control two electric fans.

From what I have read, most people use pin 42 only, why? Can anyone explain the functions of pin 33 and 42? Does only one pin turn on the fan when A/C is on? Does the PCM turn off the fans when a certain vehicle speed is reached?

I know that 94-96 B-body vehicles have two pins and fan 1 turns on when temperature is 225F and or A/C head pressure is above 189psi. Fan 2 turns on when temperature is 232F and A/C 240psi. Both fans do not come on when vehicle speed is above 45 mph or so. Does the same hold for pre-2007 trucks? Thank you.

Edited by bssfan
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Read the Manual!

 

When the PCM wants the fans to come on at low speed it grounds the green wire (pin 42); when it wants high-speed fan operation, it grounds BOTH the green and blue wires.

 

Our draft document is correct for '03-'04 PCMs, we need more practical testing and research on '99-'02 PCMs, they're a little different on the high-speed triggering. The pre-03 PCMs (one of the PCM connectors is RED) was never intended by the factory to be used with electric fans in truck applications, and as such pin 33 was meant to be used to open/close the recirculating door on the climate control system inside the cab; some guys will make their high-speed trigger wire also ground here with the intention that when the A/C is on max cool you get fans running at high speed.

 

I am not completely up to speed on the pre-03 PCMs, I have been meaning to leech all the knowledge on this from a couple other truck forums. Likewise we need to document use of our E-Fans in applications where the customer is replacing factory efans, in this case the job is very easy as all that is required is to splice our green & blue trigger wires into the factory fan control wires, and another option is to modify our fan kit to use the existing factory control harness but I have to verify the amperage/loads to make sure that the SPAL fans don't cause too much voltage drop on the GM efan harness.

 

Mr. P. :)

 

ps - forgot to add, welcome to the forum :chevy:

Edited by Mr. P.
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  • 1 month later...

Hey Mr. P,

You seem to be very informed on the E-fans. I have an 04 Denali that is Wester's tuned, and I had the guy turn the settings ON for e-fans. I have read that only pin 42 will work though. I would like to have the fans operate exactly like OEM, or however your manual states. Will my pins 42 and 33 work or will just 42? If they both wont, will an 05 PCM do the trick?

 

Also, where can I get your fan kit? Thanks!

 

Keith

 

 

 

 

 

Read the Manual!

 

When the PCM wants the fans to come on at low speed it grounds the green wire (pin 42); when it wants high-speed fan operation, it grounds BOTH the green and blue wires.

 

Our draft document is correct for '03-'04 PCMs, we need more practical testing and research on '99-'02 PCMs, they're a little different on the high-speed triggering. The pre-03 PCMs (one of the PCM connectors is RED) was never intended by the factory to be used with electric fans in truck applications, and as such pin 33 was meant to be used to open/close the recirculating door on the climate control system inside the cab; some guys will make their high-speed trigger wire also ground here with the intention that when the A/C is on max cool you get fans running at high speed.

 

I am not completely up to speed on the pre-03 PCMs, I have been meaning to leech all the knowledge on this from a couple other truck forums. Likewise we need to document use of our E-Fans in applications where the customer is replacing factory efans, in this case the job is very easy as all that is required is to splice our green & blue trigger wires into the factory fan control wires, and another option is to modify our fan kit to use the existing factory control harness but I have to verify the amperage/loads to make sure that the SPAL fans don't cause too much voltage drop on the GM efan harness.

 

Mr. P. :)

 

ps - forgot to add, welcome to the forum :chevy:

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Hey Mr. P,

You seem to be very informed on the E-fans. I have an 04 Denali that is Wester's tuned, and I had the guy turn the settings ON for e-fans. I have read that only pin 42 will work though. I would like to have the fans operate exactly like OEM, or however your manual states. Will my pins 42 and 33 work or will just 42? If they both wont, will an 05 PCM do the trick?

 

Also, where can I get your fan kit? Thanks!

 

Keith

 

That depends on weather western set the fan operation as parallel or auxilary. If the former, you can use both trigger wires and be set like if it was stock. if the later you can only use one pin and will have to find another form to turn the fans on high speed. such as the green wire from the A/C line

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Hey Mr. P,

You seem to be very informed on the E-fans. I have an 04 Denali that is Wester's tuned, and I had the guy turn the settings ON for e-fans. I have read that only pin 42 will work though. I would like to have the fans operate exactly like OEM, or however your manual states. Will my pins 42 and 33 work or will just 42? If they both wont, will an 05 PCM do the trick?

 

Also, where can I get your fan kit? Thanks!

 

Keith

Hi Keith - welcome to the forum :cheers:

 

You will have to discuss your issue with Westers, but the steps we took to program the fans is included in our manual, which can be downloaded from here. We have found that (at present) if your tuner uses EFILive they will have much more control over fan parameters than HPT.

 

Mr. P. :)

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  • 14 years later...

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