chris99gmc

Sorry to bring this thread back, but it's actually one of the only posts for 99-02 pcm's that have correct(updated) info for elec fans..

Can you confirm that this is what the function of changing the parameter to Fan#2 does in the tune??? Switching the output on pin 33 to ground??

Does anyone know what the proper setting is for fan type with this setup on a 99-01? Should it be set to Analog cycling? Or Auxiliary fans? Or...?

1FastBrick

iTrader: (17)

You need to enable the Fan settings from No Fans to Parallel Series Fans.

Under the AC parameters you need to change it from Auto Recirculation to Fan #2.

Hope that helps.

MidnightExpress99

I used same harness. Pushed blue pin into pin 42 of the ecm and tapped the AC wire near battery junction box mine is a 99 now with 34" radiator and dual gt fans and ls1fans.com harness. Everything works great. Low speed kicks on both at 218, high at 225 or 125 psi on trans and single hi on when AC clutch kicks on.

Sevex

Sooooo if I am reading this right, If I wire the fans up exactly like the picture the OP posted (with it wired to pin 33 and not tapping into the A/C wire) and switch fan settings AND A/C parameters it should work with a 99-01 ECM??

Or will I still need to use Pin 42 and Tap into the A/C wire (instead of pin 33) to get it to work?

MidnightExpress99

To my understanding and experience, I just did them on mine, I had to tap into the AC wire bc pinout differs slightly for the 03+ trucks. I did mine on 99. Dual GT truck fans, ls1fans.com harness. Pin 42 and tap ac wire. Ground point on pass side core support sucked to I cut it and grounded back to where harness grounds out on ALT bracket