Dual Fans Problem

New to the forum here and of course I come looking for help.

I have a 2000 Silverado ECSB that had a factory 4.8/5-speed setup. I recently replaced the entire running gear with an LS3/Tremec Magnum, BeCool Direct-fit Radiator and electric fans, Kooks long tubes, Corsa Sport, 4.56 gears. The fans are powered through a Nelson Performance 3-relay harness. No, I don't know which harness I have, but at the moment I don't believe it's the universal harness. My problem is with the fans.

When I first had the engine running the fans would not turn on. I even let the temp get up to 200 and they still didn?t turn on. If I turned on the A/C, both fans would run at full speed but only for a few seconds and then turn off. They would cycle like this with the A/C on. In the tune I have Fan 1 set to turn on at 199 and off at 190. Fan 2 is set to turn on at 205 and off at 200.

The shop that did the work recommended replacing the LS3 ECT sensor with the stock 4.8 sensor. I did that and now both fans run a low speed whenever the engine is running, even cold and with the A/C off. That?s what I need to fix. When the engine is off and the key on the fans don?t run.

I have two gauges for monitoring ECT. One is the factory dash gauge and the other is a ScanGage plugged into the OBD2 connector. With the LS3 sensor I read about 165 on the dash and 132 on the ScanGage after warmup. With the new sensor I read 185 on the dash and 145 on the ScanGage. The thermostat is a 186.

This morning I connected the scanner to monitor the fans and A/C pressure. With the engine cold and running, Fan 1 shows a value of On, Fan 2 is Off, and both fans are running at slow speed. I can command Fan 1 to turn on and it will run at high speed. Commanding Fan 2 to turn on only operates the A/C recirc door and does not turn on the fan.

Attached is my current tune file for review. I?m using the factory Blue/Red ECM. I?m new to the tuning world but computer literate. I appreciate any help you folks can provide.

Attachment 87008

Upon further review, it appears that the 0411 ECM from a 2002 Silverado will resolve the fan issue, but it opens up a whole new can of worms for me. If I get an 0411 ECM from the local salvage yard, is it as simple as burning my VIN into it and then flashing it with my tune? If not, please walk me through the steps so I don't screw it up. I'm assuming I need to buy two more credits to make it happen. Am I on the right track?

im not at my laptop, but sounds like the setting under a/c needs to be switched from a/c recirc to fan#2

I have it set to Fan 2 and that's not doing the trick.

Consensus around this forum and others lead me to believe my 4896 ECM won't handle the fans correctly and that I need the 0411 ECM from a 2002 Silverado. I can find the ECM locally so that's not a problem. What I need to know now is the steps to take to get my current tune and VIN into the new one.

Thanks for your help.

You just need a 02 OS. You can put one in a 4896 PCM. And you won't be able to put a 00 VIN in it with HPT if by chance you need that for emission testing.

Any idea where I can get the 02 OS? Is that a downloadable thing or do I need to see the dealer? No smog check in my part of the state, so I'm good there.

And not to change my own subject, but my version of HPT has an option to change VIN. Is that not enabled? I don't have all the bells and whistles, just the standard MPVI2 and two licenses.

00 vin in a 02 OS will create s VIN/OS mismatch. HPT won't let you create that. Other editing software will. Once it is created with another product HPT will allow licensing it though. Find a 02 truck that closely matches your maybe in the repository. But with your limited experience it's going to be difficult for you do do it right. And you really need to identify which Nelson fan harness you have. The one for the early trucks only triggers high speed fan operation when the A/C clutch is engaged. The one for the 03+ trucks can be made to work on the earlier trucks and I think it is the preferred one to use. There is even a way to make it trigger fans with A/C pressures.

Thanks for the help, 2x.

I'm told the harness is for 1999 - 2007 trucks. It's three relays with one wire going to ECM pin 42 and another going to the green wire for the A/C. I have a 2-core aluminum radiator, so I don't think cooling is going to be an issue. I just want the fans to turn on and off when they're supposed to.

So it seems to me that I have two options. The first is to update my current OS to the newer version with whatever steps are necessary to do that and then flash with my current tune. That should cost me one credit, no? I don't know how to go about updating the OS, so if you know, please tell me.

The second option is to get an 0411 ECM from a 2002 Silverado (easily done) and flash it with my tune. That should cost me one credit as well, no? I don't think I need to care about VIN mismatch since we don't have smog checks here, but it would still be good for it to match the truck. I'm kinda fussy that way.

If it's not that simple, please tell me what I'm missing and how to go about getting this issue resolved.

I appreciate your help.

one thing just came to me. you said it actuates the recirc door. That means its still wired to the recirc door, not the fans. sounds like you need to double check the wiring

Thanks, mbray. I'm going to review everything again tomorrow, but I believe you could be on to something. If I recall correctly, no matter the fan setting (recirc or Fan 2), the commanded Fan 2 on operates the door. I'll check to see just what green wire they connected and go from there. Fixing a wiring issue will sure be cheaper and easier than an ECM swap...

Quote:

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Originally Posted by 2K_Silverado

Thanks for the help, 2x.

I'm told the harness is for 1999 - 2007 trucks. It's three relays with one wire going to ECM pin 42 and another going to the green wire for the A/C. I have a 2-core aluminum radiator, so I don't think cooling is going to be an issue. I just want the fans to turn on and off when they're supposed to.

So it seems to me that I have two options. The first is to update my current OS to the newer version with whatever steps are necessary to do that and then flash with my current tune. That should cost me one credit, no? I don't know how to go about updating the OS, so if you know, please tell me.

The second option is to get an 0411 ECM from a 2002 Silverado (easily done) and flash it with my tune. That should cost me one credit as well, no? I don't think I need to care about VIN mismatch since we don't have smog checks here, but it would still be good for it to match the truck. I'm kinda fussy that way.

If it's not that simple, please tell me what I'm missing and how to go about getting this issue resolved.

I appreciate your help.

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Your harness is for 99-02. 03-07 classic harness has both fan control wires going to the PCM. You will never get high speed fan operation with coolant temp. Only with A/C compressor operation. You write entire a 02 calibration to your PCM Once that is done you can not just flash your current tune to it because it is based on a different OS. That's why I said with your current understanding of how things work it's going to be difficult for you. You will need to copy your 00 tune into the 02 OS based calibration using the editor. And you should start with a 02 OS that is from a M/T truck if that is still your truck's configuration.Starting with a 02 A/T calibration is going to make things even harder for you to do. When the PCM commands fan 2 it is going to activate the air duct recirculation because the fan 2 control was originally assigned to that function and the control wire is still in the connector. If you are going to not change to the 2 wire harness then you should set the fan 2 control parameters very high so the PCM never activates fan 2. There is no control for fan 2 anyway in the fan harness you are using. The early trucks did not use an A/C pressure sensor. They used a pressure switch that would activate auto air recirculation when the pressures got too high.

Thanks for the info, 2x. Let me see if I can simplify this a bit...

The problem that I have is that both fans turn on low speed whenever the engine is running. It's fine that both fans run when engine temp commands, but not when the engine is cold. And if both fans turn on high only when the A/C is on until I get up to whatever speed I have set, that's great. But at the moment turning on the A/C doesn't seem to have any effect on fan speed.

So the real question is can I do what I'm after with my current ECM, OS and harness? Like mbray said above, there may be an issue with the green wire connection which I will check tomorrow. But assuming I do have the correct connection or fix it so that I do, will my current setup allow me to control the fans?

You're right, I'm a complete novice when it comes to tuning and I don't want to screw it up. That's why I'm trying to be very methodical in my approach and asking a lot of questions before I go and do something stupid.

I appreciate you taking the time to educate me.

I have resolved the problem. Turns out there was an insufficient ground for the relays. The ground wires were connected to the alternator mount where the large letters tell you that's the place to connect grounds. Well, that ain't necessarily so. I left the wires there and added a 10awg wire between that point and the firewall. Both fans now come on low when commanded, Fan 2 control operates the recirc door, and when the A/C clutch engages, the fans go into high speed. The only thing left is to fine-tune the on/off temps for the fans.

Thanks to all for your responses and assistance in getting this resolved.