Fusible link - BCM is not powering up?

billbled · December 2, 2021

Hi,

I'm working on a friend's 2007 GMC Sierra 4WD, and it is not starting and not cranking. I brought the Snapon Solus Edge home from work and ran codes. U0140 and I can't talk the BCM at all. Fuses on the LH side of the dash are good for feeding the BCM.

I keep hearing about a fusible link? (Sorry - I'm not real familiar with GM stuff). I've read that it supplies the BCM.

Can someone give me a clue where that would be on this truck?

Thanks much from a newbie.

--Bill

dna9656 · December 2, 2021

A schematic (Haynes books carry a representative edition of wire schematics) can sometimes show the GENERAL location of components, think of the top of the page as the front of the vehicle. Some auto parts houses have component location info on their websites, I have asked dealer service depts. but they usu. don't know off the top of their heads, usu. a VISIT will make them feel like that have to go look it up, dealer parts guys can some times help. "ALL DATA" will most likely have it. A lot of public libraries have ALL DATA on line. GM has several manuals for it's vehicles, there is a general one, a transmission one, one for other major systems, etc. What I'm trying to say is not all the info or complete info can always be found in one book that's in your hand, if you have access to a GM CD you might find it all there. Sometimes you can find CDs for older vehicles on Ebay... I'd go to your local public library.

Kyle Ross · December 2, 2021

1.svg 2.svg 3.svgHope this helps.

if you have no com with the bcm check power and ground at the bcm.

make sure you use a good test light and not a multimeter to check for power and ground. I recommend checking power and ground using a head light bulb. The head light bulb should light up nice and bright but if it doesn't you may have a high resistance wire. 9/10 times if you have one module down and have power and ground present at the module, the module is bad.

Edited December 2, 2021 by Kyle Ross

Kyle Ross · December 2, 2021

let me know if your able too see the wiring diagrams i uploaded

billbled · December 3, 2021

8 hours ago, Kyle Ross said:

let me know if your able too see the wiring diagrams i uploaded

I am - thank you very much. I've got them downloaded, opened and printed. Looks very helpful. I'm going to get back on this over the weekend. Cheers!

billbled · December 3, 2021

8 hours ago, dna9656 said:

A schematic (Haynes books carry a representative edition of wire schematics) can sometimes show the GENERAL location of components, think of the top of the page as the front of the vehicle. Some auto parts houses have component location info on their websites, I have asked dealer service depts. but they usu. don't know off the top of their heads, usu. a VISIT will make them feel like that have to go look it up, dealer parts guys can some times help. "ALL DATA" will most likely have it. A lot of public libraries have ALL DATA on line. GM has several manuals for it's vehicles, there is a general one, a transmission one, one for other major systems, etc. What I'm trying to say is not all the info or complete info can always be found in one book that's in your hand, if you have access to a GM CD you might find it all there. Sometimes you can find CDs for older vehicles on Ebay... I'd go to your local public library.

Thanks - I've got access to Mitchell's at work - I hardly ever use it since I'm usually in other things, but you've reminded me it's there - I'll check it tomorrow.

billbled · December 4, 2021

So I checked at the connectors on the BCM today, and testing from ground on the connector to power on the same connector, I had battery voltage. This is on connectors X2, X3 and X4. Based on this I'm calling power and ground good to the BCM, and thinking that the BCM has gone bad.

It's weird - the sequence of events that led up to this:

1- Check engine light was on - unknown code - he doesn't have a scan tool.

2- My friend was trying to clear it by disconnecting the battery. He disconnected the positive lead of the battery and left it off for 4-5 days (had other things going on and forgot about it).

3- He comes back and re-attaches the positive lead, and noticed the interior lights are not on with the door open.

4- Tries to start the truck and zero. No click, no starter, nothing. Plus, now he's got multiple warnings in the instrument cluster to service different systems and things that are offline.

All this from just leaving the positive cable of the battery off for a few days. Kind of blows me away that a BCM could (apparently) go bad just by being powered down for a few days. Truck has about 150k miles on it and is in pretty good shape and has been maintained well.

So do you all agree that it sounds like the BCM is bad?

Any ideas as to why the BCM woulda quit, after reading the sequence of events that led up to this? Opinions?

thanks much,

Bill

dna9656 · December 10, 2021

Control modules need no excuse to quit, they got a pretty good union! Stray volts shot though the circuits, (a wire rubbed bare next to a ground) loose ground some place (there is a chapter in GM manuals for ground locations), a weather proof plug that's no longer weather proof. Silly stuff like that. Once upon a time modules were programmed to go bad after certain time/mileage point were passed...I don't know if that's true or not any more. Some times that stuff just goes, resistor gets weak, a capacitor opens, a diode stops working; it's usually some thing like that, you know, a $1.00 thingy goes bad in a module and it costs $239.99 to get a new one/you have to turn in the old one. It gets "overhauled" for $50.00 and the next guy pays another $239.99 for it....Life goes on...

Edited December 10, 2021 by dna9656
spelling