Will pull out the FSM in the morning and give a recommendation. Back to drinking wine now.

 

OK, I have looked at the design and there are 2 ways to bypass the BCM and actuate the motor(s). I would like to discuss these approaches with you first. Then I can scan the schematics if you like and provide them. I am going to PM you with my number so we can talk.

 

Mr Sam, turns out my switch was good, same resistance as yours. Apparently too much resistance to make the ground work. Knowing I could buy a replacement for $38 on ebay if I rendered it inoperable I decided to take it apart. Not easy but a careful use of hacksaw on each end did the trick.
Here's a pic of the board inside the switch, remember I only have the trunk switch no fog lights:






If I'm reading the resistor bands correctly, should be 787ohms with a 1% tolerance.

I soldered a short wire to circumvent the resistor then put it all back together, (needed a bit of epoxy to reassemble the switch housing).

Now back in the dash with the #1 pin on the switch connected to the light blue wire off connector C1 on the BCM and the number 6 pin on the switch to ground.

WORKING TRUNK RELEASE SWITCH!!! and no BCM replacement.

Fascinating process and it left me wondering why these have to be engineered with such complexity? At least 2 relays, resistors, circuit boards, switches, solenoids, fuses and who knows what's inside the BCM, all to pop the trunk, why not run a cable like they do for the hood?

Anyway thanks for all the advice and helpful guidance, couldn't have done it without this fantastic forum.

 

Good job Joe. Thanks for the pictures and feedback.

I guess the design team said if it isn't needed, add it. If you can make it more complicated you get a bonus, after all, we're trying to make a Cadillac with 2 seats.

 

Wanted to say thank you so much for this posting. I have the exact same problem, followed all the diagnostic steps that you took, and made it to this final step of circumventing the resister in the trunk release switch (with a wire connecting pin #1 in the trunk release switch to pin B9 in the BCM, and a ground wire connected to pin #6 in the trunk switch), and it worked! Exciting.

Now I'm wondering, what steps did you take next to permanently fix the problem? I tried plugging the switch back in, but it didn't work. Did you just buy a replacement trunk release switch and install it?

 

hi mwilkens, I did not replace the switch, just reassembled with the bypass in place. It all worked fine and then last year I was forced to replace the bcm for a host of other issues and while in the process I replaced every connector to the bcm as there was evidence of some corrosion. It’s now back to factory specs no bypass necessary and key fob will pop the trunk. An expensive proposition but the gremlins are gone.

 

Thanks for your quick reply. If I am understanding correctly, the original fault you had was in the bcm itself, correct? Even though you had to work on the trunk switch and bypass the resister, the switch itself was fine, but the resister bypass was a hack because of a fault in the bcm, right?

If that's the case, then due to the fact that I was able to replicate your test case, this proves that I have a faulty bcm as well. I also have a LOT of other lights on my dash (ABS light, traction control light, check engine, check guages) which from what I've read on the forums, are further indications that I have a faulty bcm.

I'm thinking that replacing my bcm is also the most logical thing to do. There are some further diagnostics I can do (link here), however something tells me that with this many lights on my dash, I might just be SOL. I've heard of guys getting their bcm rebuilt and "flashed". I'm wondering if that's worth it, or should I just get a new (or second hand w/ return policy) one.

When you replace the bcm you have to reprogram it, right? I saw this forum post that explains how to do it, however there is a step in those instructions that just says "... you need to reprogram the bcm." Is that something that can only be done with a Tech2 tool?

How did you go about reprogramming your new bcm that you installed?

 

With all those errors sounds like the bcm. I did not have the tech2 to program the bcm so had the stealership install. Took them a bit to actually locate a new bcm.
one thing you may want to check is for any corrosion in the connectors to the bcm. I had mice leave some acorns in the drain line behind the battery that caused some water leakage into the passenger footwell where the bcm resides. Seemed dry after clearing out the line but a few years later they were pretty corroded.