BCM Modifications for LED Bulb Replacements

[DJones]

I had long hypothesized that with the BCM controlling turn signals in newer models (my Volt was the same way) there must be a circuit in the BCM to detect the current on the output. A local salvage yard had two available, one from and Escalade and one from a Silverado, each for $40. I decided to pick one up to analyze it's circuits. I wanted the Escalade so I could also test it's programming too, but they wouldn't sell it to me because it wasn't pulled.

Here are pictures of what I found. A total of 8 current-sensing resistors 3x 5mOhm and 5x 10mOhm.

I have not done further analysis to find which four resistors go to the four corners.
What should be happening is a 0.02 Volt drop with a 2 amp load across a 10mOhm resistor. Once replaced with a value of 50mOhm, a LED bulb should drop the same voltage, preventing hyperflash.
I have not yet ordered the parts, but I figure it would be a cheaper and cleaner option than traditional load resistors. Any reason it wouldn't work or anything else I should be aware of?

 

[DougAMiller]

I like your way of thinking, but I'm not sure the turn signals are managed by the BCM. Now granted I am looking at the service manual for my 2005 Tahoe, but a lot of the systems were pretty similar for the following generation. I don't see any turn signal wires going in or out of the BCM. So check the wiring description for the BCM harness and make sure the turn signals are being controlled there. In the previous generation the signals and emergency flashers have their own module.

 

[DJones]

2003 to 2006 used a 10-pin plug in relay module, 2002 and older used a 3 or 4 wire flasher module. It probably came down to new functions like TPMS relearn blinks on the corners.

 

[Doubeleive]

BCM IS THE FLASHER ON THE GMT900'S, it even makes the fake clicker sound thru the drivers side front speaker.
my guess is it is (maybe?) only one of those, when the emergency flasher is activated led's will blink normal even if there is no resistor in place
the trickery here is that hyperflash can be disabled with 3rd party software programming so resistors are not required.

 

[DJones]

the trickery here is that hyperflash can be disabled with 3rd party software programming so resistors are not required.

Does anybody actually know what this software is?

Anyway, I swapped the BCM this morning and I got weird errors and weird operations, sort of like with my unprogrammed driver door module. I even got hyperflash with the stock Silverado program. SPS programming took less than 5 minutes and everything operates normally again.

In addition, the Silverado BCM part # is: 22846364 and my factory module is 22846365. The circuit boards appear to be identical.

I put the factory module back in while I wait for parts.

 

[Doubeleive]

Does anybody actually know what this software is?

Anyway, I swapped the BCM this morning and I got weird errors and weird operations, sort of like with my unprogrammed driver door module. I even got hyperflash with the stock Silverado program. SPS programming took less than 5 minutes and everything operates normally again.

In addition, the Silverado BCM part # is: 22846364 and my factory module is 22846365. The circuit boards appear to be identical.

I put the factory module back in while I wait for parts.

no idea on voltage but anytime the bcm is changed/swapped it has to be programmed to the vin of the vehicle.

 

[mikez71]

Hello everyone, I'm new to the forum. Bought a 2012 with 200k miles
upgrades mainly hptuners, autosync and a tech-2.

Autosync (btdieselworks.com) with BCM programming is supposed to take care of hyperflash. I do see it in their programming options. I purchased one just a few days now with the BCM programming so that my door locks wouldn't autolock. Has a few other features I really like..

autosync unit:
extra engine/trans guages in display
TPMS warning disable
manual fast idle
check rear camera by pressing down on the mirror adjuster
remote window up/down
afm disable?

BCM programming option:
approach and exit lighting
door locks
Extended accessory power lets me close windows after key out for a few mins.
DRL

I haven't tested all the features yet, I think I just figured out I have to update firmware before updating BCM module everytime you make changes. about to test speed sensitive wipers.

Costs about $400 with autosync

Not sure if there are other options out there, but I had been looking to disable the door locks ever since I bought this truck a few months ago. Finally found it at btdieselworks. Don't work there, don't know them but am a HAPPY customer 3 days now. Probably more than you want to spend just on lights if there are other options, but the door locks was the big one for me.

 

[DJones]

I haven't posted in a while because life got in the way. I looked into custom BCM programming solutions but couldn't justify the cost.
Here's what I do know:
1. The shunts aren't for the bulbs.
2. My next step is to buy the 3-day subscription to the service manual and trace some wires.

Not sure when I'll get to it.

 

[iamdub]

I haven't posted in a while because life got in the way. I looked into custom BCM programming solutions but couldn't justify the cost.
Here's what I do know:
1. The shunts aren't for the bulbs.
2. My next step is to buy the 3-day subscription to the service manual and trace some wires.

Not sure when I'll get to it.

Following this.

 

[DJones]

Tackling this project again, here is what I found:
1. Each bulb is controlled by an 6143D MOSFET. The MOSFET has five pins, one of which is a current sense output.
2. It appears as if the Escalade "Lamp Outage Detection Signal" pins may actually be useful.
3. I look at the board too much and eyes go crossed. It may also have more than two layers, which would explain vias unrouted on the opposite side.

I'll do some brute-force testing this weekend to see if I can come up with anything.

 

[Joseph Garcia]

I kept the hyperflash, because it is more noticeable to other drivers on the road around you, and isn't that the purpose of a directional after all? I will note that hyperflash is illegal in some states, though.

 

[2fatowing]

I like your way of thinking, but I'm not sure the turn signals are managed by the BCM. Now granted I am looking at the service manual for my 2005 Tahoe, but a lot of the systems were pretty similar for the following generation. I don't see any turn signal wires going in or out of the BCM. So check the wiring description for the BCM harness and make sure the turn signals are being controlled there. In the previous generation the signals and emergency flashers have their own module.

I know I am late here but no, you are very incorrect. Starting 2007-2014 the BCMs function very differently. And CANBUS was in its second iteration then if I'm not mistaken. I probably am with the CANBUS thing. But not the BCM. Older models had a turn signal switch and a relay. Really simple stuff. Then, for some reason, prob because they wanted the blinker sound to sound less mechanical, less like a relay jumping on-off-on-off. Now it's tick-tock-tick-tock through the speakers of your car. I had a Cavalier one time when I began 12v installing professionally, and I despised GM so much for adding their factory CANBUS interface that kept all factory communication with the BCM, but at the point of hardwiring it and bypassing that CANBUS interface that made that install harness almost as expensive as some of our entry level single din radios but themselves, we were talking about maybe the blinkers not making any noise but operating fine, and maybe your check engine light and/or airbags might not work but on my own Cavalier, I refused to pay that $90 for that harness back then because that's how much it was and most shops weren't hardwiring any longer. I sure as hell was gonna do just that. I got all these cool new logins from my new job at the shop that gives me entire wiring diags plus their locations and later pics, and how to do stuff. So I decided I'm just gonna grab a fluke and a 9v battery to pop the speaker wires against what these diags told me the were and also verified in other ways that I wasn't blindly doing too much. But yeah. way different tech. It seems as though that number 2 in front of what year we're in made it so that nothing in vehicles was ever allowed to remain mechanical, or at the very most, minorly technical with much smaller micro relays and such inside and some caps and resistors but not much more. Now each system is its own freaking computer. Man i sound like an old man right now. Some would say I am at 40. I feel old but same. If anyone was wondering.