Possible bcm issue on 2002 gmc yukon denaliXL 1500

[nickardo]

I have had growing electrical issues with my yukon first it was the brake lights going out (exept the 3rd light), I swapped the brake pedal switch hoping it would fix it, it didn't. Then my headlights went out so I went to my friends house to try and at least diagnose the issues but he pulled the IGN relay while the truck was running but put it back before it died and after that I realized my security light was staying on and I lost control of the interior lights and exterior lights completely, along with that the door chime no longer sounds and my rear wiper no longer works, everything ive read brought me to the bcm grounds or the bcm itself, I checked the grounds and they were fine I tightened them more regardless, and I swapped the bcm with a pre programmed bcm but that still didnt fix the issue, I later realized I didnt swap them correctly by waiting 30 minutes with the battery disconnected, but recently my other friend hooked up a scanner and went through my vehicle to find any bcm codes or anti theft codes and it said I had no communication to the bcm or anti theft system so he tried clearing the codes hoping it was a fluke in the system but it didnt change anything and after I shut the truck off and tried to turn it back on it ran for maybe a second then shut off I dont know whats going on or how to fix the issues I have please help.

[Jsdirt]

You need to make sure ALL BCM powers AND grounds are not only carrying voltage, but are able to carry AMPERAGE. With computers there's usually more than one power and ground.

 

Connect a halogen headlight to each one and make sure it powers it - do this for BOTH the powers and the grounds. If it can't power a light, there's a wiring or connection issue somewhere.

 

If this is a vehicle 2014 or newer with Global-A architecture, you have caused yourself all kinds of problems by installing a used BCM ... so I really hope your truck is older for your sake.

[nickardo]

3 hours ago, Jsdirt said:

You need to make sure ALL BCM powers AND grounds are not only carrying voltage, but are able to carry AMPERAGE. With computers there's usually more than one power and ground.

 

Connect a halogen headlight to each one and make sure it powers it - do this for BOTH the powers and the grounds. If it can't power a light, there's a wiring or connection issue somewhere.

 

If this is a vehicle 2014 or newer with Global-A architecture, you have caused yourself all kinds of problems by installing a used BCM ... so I really hope your truck is older for your sake.

Its an 02 so I should be alright, I ordered the bcm from Highway 71 out in Minnesota, how should I go about using the headlight to check voltage and amperage and couldnt I use a multimeter or power probe? Im not the best at electrical especially not on light duty automotive and what power and ground should I use for the bcm? I dont know if there's more than one 

[Jsdirt]

Ok that's good! You'd have been royally screwed on a '14+!

 

I use old school sealed beams since they're easier to work with ... but most people don't have those laying around anymore. Any halogen headlight will work, but you'll have to BE CAREFUL not to touch the bulb - not only because it'll burn you, but it'll also burn the thing out, too. Even an old bulb that doesn't have a functioning low or high will work. As long as at least ONE filament is good, it'll work. Wiring is easy enough to figure out on the net depending on what bulb model you're working with.

 

Once you figure out which is power and which is ground on the light, now you can test with it. To test the power, run the ground prong on the light straight to battery ground, then touch the bulb power prong to all of the power wires one at a time. If they light up nice and bright, they're good.

 

For the ground you do the opposite ... BUT it's safer to just grab 12V from the cigarette lighter / power point or fuse box (choose the higher amp fuses), then touch the ground prong of the light to the BCM ground. If it lights, the ground is good.

 

You;ll have to be more careful with 12V on a wire, since if it touches ANY metal, it'll either blow whatever fuse you're connected to, or it'll go from ambient to 1,000°F in a SECOND if you're pulling from the power side of the fuse (or getting unfused 12V). Just keep that in mind and be mindful - don't let it touch ANYTHING but the light's power prong.

Edited March 26 by Jsdirt

[asilverblazer]

14 hours ago, nickardo said:

Its an 02 so I should be alright, I ordered the bcm from Highway 71 out in Minnesota, how should I go about using the headlight to check voltage and amperage and couldnt I use a multimeter or power probe? Im not the best at electrical especially not on light duty automotive and what power and ground should I use for the bcm? I dont know if there's more than one 

I'd put the factory BCM back in. Conduct further careful tests - BCM's don't just go bad or fail.

 

Given the assortment of lighting issues, I suspect, corrosion in a connector somewhere or somewhere in the wiring harness.

 

First place I would look is the under hood electrical center on the drivers fender. Check the underside of it.

 

Also, be on the lookout for rodent damage.

 

Lastly, using a wiring diagram - you might try unplugging the 'outputs' of the BCM and probing the BCM to see if it is out putting signals where/when it should.