I'm really just here to vent. I got my efans in my new to me 04 Tahoe tonight. Everything went well until I hooked up all of the wiring. I have the stock harness from the truck the fans came out of but it wqs cut up so I just spliced it back together. i noticed that there was no ground which must have just been part of the harness that I didn't get. So my fans didn't work at first. So I looked up the schematics and could see that I just needed to splice a ground into the black wire going to one of the fans. I did it and then the fan came on but it was LOUD. I turned on the AC and the other fan didn't come on. I commanded both fans on with my HPTuners and they both came on and were actually quieter but when I just let the teuck take over it would just command the one and it would be blasting. It was unacceptably loud. So I was messing with it trying to figure out if things were right and then the fans just turned off. The PCM was still commanding them on and nothing I did would get them on. So I don't know if I blew a fuse or a relay or if the fans burned up. I guess I'll have to figure it out tomorrow. I might just build my own 2 relay controller for simplicity. It's late. I can't mess with it anymore

 

Are you sure you spliced into the right wire and the fan actually isn't turning backwards? These fans are loud, but they move a ton of air. I didn't think you could hear them in the cab.

Has your tune been adjusted for the fans? When one is on high and the other is off that means the "high" trigger is on but the "low" is off.

 

I'm not 100% sure I spliced into the right wire, in fact I think I didn't and I fried something. Based on the Schematics I found that had wire color and everything, it should have been the black wire. It grounded one of the fans and one of the relays. I did set the tune up just like a stock 05. The weird thing is this,
1. If the PCM was commanding fan 1 on and fan 2 off - One fan came on full blast
2. If the PCM commanded fan 1 off fan 2 on - No fans ran
3. If the PCM commanded fan 1 on fan 2 on - Both fans ran half
So I know that's not what's expected. Maybe PCM wires were switched to the wrong pins, like fan 1 and fan 2 controls were switched but I'm not sure how that would cause it to do what was happening.

Now something is blown and I don't know what so I'll build my own harness. I checked one of the fans by hooking it up directly this morning and it came on so I know at least that fan still works. I also switched the fans before I did that and tried commanding them on and nothing happened so I'm almost 100% sure it's the harness that's broken.
I'll build a 3 relay harness tonight. It seems like the Nelson harness doesn't use any fuses but I guess I'll probably use them. Also, the fans are very dirty from the junkyard so maybe that's contributing to the loudness.

 

The trigger wires are ground activated, so try connecting the low speed direct to ground and they both should turn on low. When you connect the high speed and low speed the both should turn on high. Just the high speed wire grounded should make 1 fan come on high.

Did you change the fan type in the tune or just the turn on settings? Its on the next tab than the temp settings.

 

That's a great idea. I already cut the yellow and gray wire to one of the fans but I may splice it back together. . Actually I'm pretty sure it's not going to work until I build my new harness since I already burned something up but when I build my new harness I can test it like that. Thank you for the suggestion. It does sound like I have my PCM pins switched so when the computer commanded "Low" it was actually grounding the one high speed fan. Dammit! I wish that hadn't happenned. I have a lot more work to do now.

I did change the fan type to "2 Fans" in the tune.

 

PCM never commands one fan on and one fan off. When it commands fan 1 on they should both run low speed and when it commands fan 2 on they should both run high speed.

 

Thank you guys for the help. I think I had a few things going on. I might not have been getting a good hot on the post I hooked up to. I changed the 40A fuses on the harness and got a good hot and ground and tested the fans and relays by grounding the signal wires and they both worked. So hooked up to a good tested hot (on the fuse block) and switched my signal wires to the correct pins (green wire to blue pcm connector and blue wire to green one) and everything works fine now. I just need to clean up my harness now. I cut and spliced stuff together while testing stuff and made a mess. Easy fix now that it works. Thanks again for all the help.

BTW 2xLS1, you're right but if you wire your pins backward it commands fan 2 on full blast as "Low". Getting the pins right made it work just as you described.

 

Not quite. As I stated:

Fan 1 (low) on is both on low
Fan 2 (high) on is 1 fan on high and the other off
Fan 1 and Fan 2 on is both fans on high

 

There is never a condition where the PCM outputs a ground on fan 2 control without still outputting a ground on fan 1 control so my statement is correct.

 

Most pre-04 aftermarket/modified harnesses work off 1 fan pcm control and the high speed is controlled via the ac clutch. Not the best way to do it, but that is how a lot of them set up, and in that case you can have the "high" trigger engaged without the "low" being triggered if you use the AC before the engine is up to temp.

Thats not totally relevant here, but your first statement was ambiguous. Just saying when Fan 2 is triggered the fans are on high is not necessarily true because you need Fan 1 on activated in addition to Fan 2 for that to be the case.