I think my internet search skills are failing me today so I apologize for this in advance.

I'm hoping someone has some specific experience tuning efans in a 2001 Silverado. I have read some posts about that specific year of pcm where pin 33 is positive and not negative. I have a licence for my pcm on hptuners and I have successfully done a 4L80e swap with it but I am lacking in the knowledge as to how to tell it to use pin 33 for a fan control.

I wired it up based on this diagram below. If anybody could help I would very much appreciate it. Thanks.


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Wire it up as shown and in HPTs in the fans section set the low speed and high speed temps to whatever you want.

 

I don't need to enable pin 33 or anything? If not then something is still wrong. I was just out there and I am able to command the fans on but unless I command them on, relay 2 and 3 repeatedly click on and off.

 

There is a different way to hook up the fans for 99-02 and 03+. I have a 03 and I plugged into pins 42 and 33 . My wiring harness is the same as in the diagram in OP so I am thinking you have the wrong harness? you will need the one for the 99-02 trucks , which i think do not have plug and play pcm trigger? Sorry I only researched for my 03 truck. i think for 99-02 you have to splice the harness into an existing AC wire? I am just guessing from vague memory when I was doing some research.

_Zblee

 

this is what you need, there is no pin 33 , there is a wire to connect to AC wire.



where the 03+ harness has the pin 33

 

Well, that shouldn't be much of a change to the harness. I built it myself, but I assume that the wiring should be the same.

Now I just have to figure out where the A/C tap comes from.

Thanks for the reply.

 

If this is how you wired it, then you should have no problems once you get the settings correct in the tune. First question, what did you do with the wire that was in pin 33 to begin with? I removed mine and taped it off. You probably should do this.

You need to set the Recirculate Option to Fan#2





Then set all the other fan parameters (These are based on 2002 Camaro and have served me well):

 

99-02 A/C single pin Blue 42 triggered applications. Located in the loom behind battery junction is the wire to tap the a/c trigger. Locate the green wire. This wire may be light green or green w/ white stripe. Use a test light or volt meter to find the wire that triggers the passenger side fan over the A/C condenser to come on high speed when the A/C is turned on. CAUTION YOU MUST USE THE PROPER GUAGE WIRE TAP AND CONFIRM YOU HAVE THE RIGHT GREEN WIRE FIRST. FAILURE TO DO SO HERE WILL RESULT IN TROUBLE!. DO NOT TAP UNTIL YOU CAN CONFIRM YOU HAVE THE CORRECT GREEN WIRE. If the light dose not come on when you turn on the A/C, it not the correct green wire. Once you have located the correct green wire, then go ahead and tap it. Once you tap it, use your test light or volt meter to recheck and confirm proper operation (fig.4) Use pliers and a small flat head screwdriver, remove the grey harness retaining cover from the top of the blue PCM connector. Use the small flat head to pry the grey retaining tabs out. Flip the connector over and Remove the PCM. The black cover should pull off by pulling outward on the cover, releasing from the two plastic tabs. Take your 7mm socket remove the blue PCM connector closest to the engine. Use pliers and a thin pick or screwdriver, press on the white retaining tabs on each side of the blue-clear cover and pull it off. Lubricate the PCM pin and wire on the harness tagged BLUE 42 using vaseline or die electric grease. Gently push Blue 42 trigger through pin 42 on the PCM until it secures itself. You can see it though the clear plastic. It should should line up and look uniform like the rest of the pins. GENTLY, pull on it blue42 fan harness wire to seat it and make sure it is secure to not back out when reinstalling the retaining covers. Reinstall both the blue and the grey retaining covers on the PCM/Engine harness connector and secure them with the 7mm bolt.(fig.5)
This is from LS1fans.com for more info. I have an 03 truck and used this guys harness and instructions.. Good luck man!

 

If I'm not mistaken, tapping into the green trigger wire will keep the AC compressor relay energized all the time.

I know the pin 33 is not used for the 99-02 trucks because it is a positive output from the PCM. What is stopping me from using a 4th relay to switch the polarity from positive to negative?

If I hook the positive output from pin 33 on the PCM to pin 86 on this switching relay, pin 30 on switching relay to pin 85 on left fan relay and pins 85 & 87 on switching relay to ground I should be covered. Then all that is left is to do some HPT tuning.

 

Pin 33 IS used on some of the 99-02 trucks for auto recirculation.

I don't know if that pin is positive or ground in that configuration, but I guarantee you it is a ground when you switch the setting to FAN#2 in HPTuners.