2012 Yukon XL Denali possible BCM issue

[Dkd71]

This has me stumped, the courtesy lights illuminate with the doors open or when I rotate the dimmer control knob to it's detent at full on..as they should. However they will not turn on with the press of the map light/lens button when the doors are closed and the courtesy lights have dimmed out after a few seconds...this goes for all of the map lights. If the courtesy lights are on, when you press any map light/switch the light will turn off and my instrument cluster lights will dim..same if I open the vanity mirror flap.

 

I have checked the grounds at G200 and G201, both are clean. I have 11.9V at the red wire in the overhead console but 10.5V on the orange. If I probe the red wire to ground it goes from 11.9V with headlights off, and to 11.7V when the headlights are tunred on, if I probe the orange wire I get 10.5V with the lights off but 6.3V with the lights on.

 

I have probed the overhead black wire to both G200 and G201, if I probe to G201 I get .7 megaohms resistance but after a few minutes that steps down as modules go to sleep, after about 25 sec it drops to 360 ohms then to 210 ohms then down to .4 ohms.

 

I have cleaned the gronds under the RF radiator support, the grounds at the LR of the frame.

 

The only thing that comes to mind, is about a year ago, my LR was hit and I didn't notice any damage behind the bumper, about 6 months later during heavy rain, I would get random parking sensor blocked errors on the DIC but the sensors still worked. Later on the LR sensor stopped working and I had a code that came up in the Tech 2 as:

 

 

 

I did disconnect all 3 connections at the module in the LR cargo area and my issues still remain.

 

I have reseated all the junction block connectors behind the left and right panels in the front door area at the dash, not sure where to check or if the shorted sensor caused an issue with the BCM.

 

 

Everything works in the vehicle except the map lights dim the IC lights when pressed but no light turns on, and the obstacle avoidance is not working until I replace that sensor.

 

All input and criticism appreciated.

 

 

 

[asilverblazer]

I doubt the BCM failed, I've never heard of that. 

 

gmupfitter.org has wiring diagrams that might be of use.

[carkhz316]

1 hour ago, asilverblazer said:

I doubt the BCM failed, I've never heard of that. 

 

gmupfitter.org has wiring diagrams that might be of use.

Are you meaning for the parking sensor/ dome light issue or in general?

 

If the latter, I've replaced dozens of BCMs across GMT 800 through K2 trucks for a variety of concerns and failures.

[asilverblazer]

17 hours ago, carkhz316 said:

Are you meaning for the parking sensor/ dome light issue or in general?

 

If the latter, I've replaced dozens of BCMs across GMT 800 through K2 trucks for a variety of concerns and failures.

I've never seen or heard of a BCM failure in any GMT800 and up truck.

 

What do you do that you've come across so many?

[Dkd71]

I was looking at this schematic and it appears the orange and gray power the front seat map lights while one is on the other would take over when pressed resulting in a constant light when the door was open. With mine if I turn on the map light the light shuts off and the IC lights dim...same as if I press any map light or open the visor mirror.

 

 

 

 

 

 

[Dkd71]

Well, I found what appears to be the issue...lol. I have been doing this for a long time, and I know I pulled both the fuses in the I/P fuse block #5 & 17 and both were good. I have since reseated many junction block connectors and removed the NEG terminal about 3 times to clear the system. 

 

Anyway fuse #17 was blown and I know I would have seen it, but I don't know if moving stuff around casued a surge or I missed the fuse, I'm 99% I didn't but I can't say for sure.

 

So all is good for now, we shall see. 

[Jsdirt]

Doing this kind of work always gave me a migraine from hell. All the complexity and wasted hours pouring over diagrams, highlighting a half million circuits, only to find something just like this. That used to make me lose my mind!!

 

Glad I closed my shop, lol.