Someone told me some time ago I needed to have my H2 reflashed with Denali or Tahaoe features to utilize the stock fog light switch. I've been told the same thing for replacing my stock fan clutch with electric fans. I got a pigtail from the junk yard to work with the stock switch, but I haven't had any luck finding a wiring diagram to figure out the wiring harness beyond the wiring for the rear windshield wiper portion of the switch. I found a foglight relay to fit in the foglight spot in the fuse box and even found a video showing how to wire it in the back of the fuse box, but I still couldn't get the foglight switch to work. (although, i got the light to come on, but it stayed on and wouldnt go off with that setup). I presume this has to do with the wiring needed for the negative trigger of the BCM that you mentioned. You're definitely right about the 03-07 H2s NOT having any place to activate the fog light function in the BCM. My H2 is an 06.

I didn't understand your remarks about the "Latching Relay." Were you saying that I can bypass the BCM & make the stock foglight switch work independently of the BCM with a latching relay? If so, please give a detailed explanation that a lay person like me can follow. Thank you kindly.

 

Latching relay setups can be somewhat complicated. Simplest would be a bistable pulse type but those run $50 or more. Pretty much all latching relays require two separate momentary push buttons. What would really be needed would really be called a soft latch switch which would need to be built. I'm not sure if an off the shelf one is available but probably is. It basically used a couple of transistors, capacitors, etc to switch the transistors on and back off again. https://circuitdigest.com/electronic...switch-circuit

There might be other ways using multiple standard relays but I'm not certain and it would take me a bit to try and wrap my head around the idea.

The use the BCM would require reprogramming it with as you mentioned, software for a different vehicle. The only way I can think you might be able to do that would be to use a custom bench programming harness and use the VIN for the other vehicle or simply use a BCM from a donor SUV. The problem though is there might be unintended consequences as some of the modules in the H2 are specific to the H2 only like the DDM, air ride, etc. so certain things might stop working. For example, the DDM (on 05-07) has a global windows function which is exclusive to the H2 while those same buttons on an SUV are for power pedals in/out. Oceanbrave on here I belive is an electrical engineer. Maybe he has some ideas.

For using the actual factory BCM the only thing I can think would be to physically remove the BCM, get a chip clip and dump the eeprom, decompile it, modify it, and write it back which no one is likely going to attempt to do. I did consider really digging deep into the TIS2000 software and trying to locate the actual various modules firmware and seeing if I can find the correct file that way and then try to decompile and poke around. If that is doable then it might be possible to then copy it back to the TIS2000 and then use TIS2000 to program a new BCM with the hacked firmware.

 

Man, you are waaaaay more advanced than me. That's just too much trouble for one button. Why can't i just locate the specific wires for the button on the pigtail and connect them like a regular switch & circuit with the fuse, relay and power. Is there anyway to just do this like a regular switch?

 

The issue is with trying to use the factory fog light button from one of the SUV's. If that were a latching push button (press and it stays in and connected, press again and it pops out and disconnects) it would be simple. Problem is that the factory style fog light button is momentary contact only which greatly complicates using it without the BCM computer. With just a regular relay you would have to hold the button for the fog lights to stay on which obviously would not work. The simplest solution would be to not use a factory button and just install any aftermarket toggle switch/button in our original rear wiper **** panel in the blank spot where the factory type button is on the SUV's then just use a regular relay (could still wire it to the factory relay in the underhood fusebox which we do have).

 

Bingo. That's what I will do..great explanation.

 

I was curious so yesterday evening I tried poking around some with the Tech2. I connected it to the H2 and told it to do an update which polls all of the modules and saves the to the linear PCMCIA card in the Tech2. I then took the card out and put that in a laptop with the memory card explorer software (a linear pcmcia flash card cannot be used like other memory card) to write out a bin file of the card. Then put it back in, connected the Tech2 to the laptop and ran TIS2000. It will not let you do an update if no modules are changed so I selected to change it to non-power folding mirrors so it would at least write something back to the card. Then back to card explorer and wrote out another bin file to compare and poke around some. I'll reset so it does not actually update anything on my H2 but on a quick look and doing a compare, there is a difference in the bin file but with a 32mb file that is a LOT to dig around in. I can find my vin number stored no problem though. Not likely to be fruitful though as I'm not a coder. I can id things and can see some C++ library references though so someone who knows how to decompile C++ might have a way to figure things out. Maybe not though if it is encrypted. Does not appear to be as all of the things like my VIN and text on the Tech2 screens are all in plain text in the bin image.

There is only one guy I know of in the entire world who has figured out GM body control modules and can hack them and he charges for the service. You have to tell him what you want modified and send him a BCM and he will send it back to you.

 

WOW, WOW AND MORE WOW...you are pretty advanced...i've just decided to open up the switch and remove the nonlatching fog light switch and put in a factory looking latching toggle switch. I hate to do it this way, but it still looks factory and its just tooo much trouble for one button. Do you think I'm going to have to go the BCM reprogramming route for converting from a fan clutch to dual electric fans? I've heard the electric fans, like the factor fog light button is NOT push and play.

 

No, but..... Electric fans are controlled PCM and you will have to get your PCM re-programmed by a tuner to enable them if you are going the route of a factory fan harness from a 2003-2007 GM truck or SUV. That is the best way to control electric fans by the way. The PCM has all of the ability and setting for electric fans, they are just not enabled in the PCM on vehicles that did not come with them.

For what its worth. I've done the conversion on several GM trucks already. Ideally you also want to get the other underhood fuse box shroud/cover that has the secondary small removable cover on the corner near the firewall but really not needed since you have to remove the fender brace to open it anyways. The factory relay/fuse block for the fans mounts under the fuse box shroud in that corner. There are a couple of regulars on performancetrucks forums who carefully remove the harness from junkyards and sell them (not easy since the wiring is also tied in with other wiring and they do it right separating the harness). The power comes from the stock fusebox aux stud, and there are two wires that have to be connected to the PCM in two open spots. Then get the dual 7 blade factory fans. You will also need to either replace both of the oil cooler lines and one of the trans cooler lines with those for a 08/09 H2 or cut/modify your existing lines since they will interfere with the electric fans shroud.

I actually have everything here to do mine (including a new all aluminum 2 row radiator) which I will be doing very soon... probably will install it all in about a month. I also have a full EFILive tuner so enabling them in the PCM is simple for me to do. Overall if the harness was properly removed (PCM pins, carefully removed and not cut off or anything) its not a very hard conversion but the oil and trans cooler lines complicate things as does the custom tune modification needed.

 

Man, you must be a professional mechanic. Your comprehension is so thorough and has me beat by a mile. I wish I could just drop off my H2 with you & pay you to complete everything on my wish list. By the way, is there any way to turn that factory fog light switch into a latching switch? I plan to open it up this weekend. If I can't re-rig it competently, I plan to remove the OEM foglight switch from the hole, drill a small hole out the back to run wires and put this 3pin latching switch in its place: . I'd rather have the push button, but this will be as close as I can come to preserving an OEM factory look without going into the BCM. I'm a bit uneasy about sending my BCM off to someone. That takes a lot of trust. Someone messes up anything with that and you're screwed. Where is your guy located? Does he have a website?

On the electric fan conversion, I noticed you specifically mentioned the 08/09 gen 2 H2, but do you have to do anything with the oil & transmission cooler lies on a gen 1 06 H2? Also, why did you get an "new all aluminum 2 row radiator."? Is that something I need to do too? Which EFI Live Tuner do I need to get and is operating it pretty simple? I've never used one before

Finally, can you please explain the difference between BCM, PCM and ECU?

 

If you know someone with hp tuners, they can enable the electric fan to function. There are many places online that provide this service. You'd have to mail your pcm to them however. If you are close by I could do it for you.