Im at a loss here. I had wheatley send me new pcm under the assumption the 0411 pcm in the truck had a short or something to that nature in it for the efan pin. Well being the good guy he is, he sent me one out and I got it in and still nothing. when commanded on low it turns on. when commanded on high the relay clicks and clicks, AND NO FANS!... Anyhow with my stock pcm that I threw in to see if maybe the 1st pcm was bad, it works as it should. Only thing I can come up with at this point is the 0411 pcm is pinned in a different spot for the high fans than the 99-00 pcm. When I ground the pins manually they work as they should also. Any help would be greatly appreciated.

 

I failed to mention these are OEM fans and the relay harness is also oem.

 

Are you using pins 33 and 42?

 

Bad relay maybe?

 

The wiring is different on the 05 up from the 99-02 trucks. The way it energize the relay is different.

See this thread as it shows how to do exactly what your referring to. https://www.performancetrucks.net/fo...-chevy-484892/

If you are 100% sure the wiring is correct, the Relays are good, and the fan motors are good, Then check with your tuner and make sure the fans are set up correctly in the tune for how they are wired up.

 

Are you removing the pin from C2-33 or splicing to it? Remove that wire and don't use it. Install your fan wire directly into C2-33.

Jeff

 

I have removed the pin completely!
The relay and fan motors are definetally good as everything worked fine with the stock pcm

 

Thanks everyone, that link from 1fastbrick helped a lot. I think what's happening is when I'm commanding high the relay clicks because its hitting it with 12 volts. It needs negative and not power. So I either need to add the relay to switch the activation from power to ground and leave it in c-2 33 or splice it directly into the green a/c wire. That's where I'm still confused. Because with the old stock pcm its fine. I'm wondering if the pin 33 gets energized with the a/c on, with the 0411 PCM. I'll have to check it out today when I get a little time.

 

The pin you are trying to use for fan 2 control on the 02 and older PCMs is used for A/C Auto Recirculation control. I use Tuner Cat OBD2 on those PCMS and I have the ability to reassign that pin for fan control in the calibration. I believe HP Tuners allows you to do that with a version of their 2.23 beta and now with 2.24 available. I don't know if EFI Live does.

 

So is there a reason it works the way it is now with my original 2000 PCM and not with the 0411 I have in it now?