Tuning for 05+ fans on '01 Silverado 4.8

[TurboWT]

Ok guys my tuner and I have been working on this issue for a while and hope you can help me shed some light on it.

I have a 2001 Silverado 4.8/4L60E without A/C and installed a 34" radiator with electric fans out of a 2010 silverado (has the built in oil cooler in radiator). Anyway here's my issue.

I installed this setup with a harness from Black Bear Performance. Its the type that has the one blue wire to plug into pin #42 in the PCM, and the green wire that you splice into the green wire in the harness running near the alternator. Threads say that it's either the green or green/black stripe wire that is used for high speed. However the green wire doesn't work and I have no green/ black stripe wire, but there is a green/ white stripe wire, also doesn't work.

So here's the problem, I only have low speed operation and no high speed. Every thread I've found are on rigs that have air conditioning and that is suppose to activate the high speed. We tuned the PCM for use with two fans, probed the #33 pin that is suppose to operate the high speed and still nothing.

The problem is that everyone talks about using the AC pressure for activating the high speed, but since mine doesn't have AC I'm not sure how to activate the high speed operation in the tune.

Sorry if this is repetitive and doesn't make sense, but I'm new to this and trying to learn! Any help would be appreciated.

[PitchblackC3]

If you don't have the beta, email support and get it.

Once you have it look under SYSTEM->A/C->GENERAL-> Recirc Option

Change that from AC recirc to Fan #2. That will activate pin 33 for high speed.

[AKlowriderZ71]

If you don't have the beta, email support and get it.

Once you have it look under SYSTEM->A/C->GENERAL-> Recirc Option

Change that from AC recirc to Fan #2. That will activate pin 33 for high speed.

Thank you for the help. I'm helping the OP with this, so I'm watching this thread. I've already switched the AC recirc to "Fan #2", and wired the high speed to pin 33 in the red connector.

He still has no high speed fans. I can command the low speed fans on with the HPT scanner, but the high speed fans will not command on.

Anybody?

[PitchblackC3]

I see the problem now.
If that black bear harness is made to tap into the AC circuit you will have to rewire it because it is looking for a 12v+ signal on the AC wire to activate high speed. The PCM outputs a ground (-) signal for high speed.
On the high speed relay the 85-86 control circuit needs to have 12v+ constant with the (-) triggered by the PCM.
Once you swap that it should work fine.

[AKlowriderZ71]

That makes sense to me. I'll check that relay harness & give that a shot, but it may be a few days before I see the truck again.

Appreciate the help.