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Discussion Starter · #1 ·
2002 Envoy extended no dash illumination. Bought last week in an online auction. Trying to figure out why the dash illumination lighting is inop. The dimmer works for the hvac, radio, prnl. I've done some poking round, all fuses are good. DTCs show codes related to communication, or loss of. Any possible common problems with this condition? I'm thinking the BCM is the problem.
 

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The cluster backlighting has 8 bulbs, grounded to the splice pack at G201 which is under carpeting on the passenger side of the center console. Also could check at the cluster harness connector. Do you have the wiring diagrams yet??

Edit: since your other lighting works that at least suggests the ground is good as they all share that G201 ground point.
 

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I'm thinking the BCM is the problem
The BCM has two separate outputs for lighting. One for the standard bulbs and a second for the LEDs.

All the standard bulbs share the same output I think. So that would point to the cluster harness or a fault on the cluster board itself which I hear is not uncommon.


The LEDs that are used for 4WD position indicators, the headlamp ON indicator, traction on amd traction disabled (if equipped), and front and rear fog lamp indicators are controlled separately by the BCM from the standard bulbs.
 

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Discussion Starter · #4 ·
The cluster backlighting has 8 bulbs, grounded to the splice pack at G201 which is under carpeting on the passenger side of the center console. Also could check at the cluster harness connector. Do you have the wiring diagrams yet??

Edit: since your other lighting works that at least suggests the ground is good as they all share that G201 ground point.
I have no power at the cluster (a7) brown/white strip. G201 is good as all the other systems work as designed plus I power light tested that ground circuit. The dimmer will work on prnl, radio, heat/ac. Those I assume are LEDs. Thinking about jumping 12 volts at the cluster to see if the 12v backlighting will at least work. I have codes concerning data link communication problems but at this point I have to cipher. It's been awhile for me with this stuff. The wife sells at a Buick dealer so I may give up and use her employee discount to have it diagnosed. The wiring diagram shows the final control for the illumination lights is the BCM. I'm going to attach my Snap on Solus, which I finally found packed from a recent move, and concentrate on the BCM. I'll keep you posted. Just as soon as Michigan goes up two scores on Northwestern. Retirement sucks.
 

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Discussion Starter · #5 ·
The BCM has two separate outputs for lighting. One for the standard bulbs and a second for the LEDs.

All the standard bulbs share the same output I think. So that would point to the cluster harness or a fault on the cluster board itself which I hear is not uncommon.


The LEDs that are used for 4WD position indicators, the headlamp ON indicator, traction on amd traction disabled (if equipped), and front and rear fog lamp indicators are controlled separately by the BCM from the standard bulbs.
So neither of the light circuits coming out of the BCM is working. I am going to scan the system here in a few with a Solus. I'll get back with you all hopefully with data comm codes. Please pray for my sorry ass. No more auction cars.
 

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The dimmer will work on prnl, radio, heat/ac. Those I assume are LEDs.
The LEDs are as I listed previously according to the wiring diagrams.


neither of the light circuits coming out of the BCM is working
Did you test this with a meter at the BCM??

Do you have an OBD2 Bluetooth adapter?? I am not familiar with the Snap On scanner(s) so I don't know if they will show data parameters like the dimming input the BCM is seeing and so forth. I can do this with an android app and bluetooth adapter.
 

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Discussion Starter · #9 ·
2002 Envoy extended no dash illumination. Bought last week in an online auction. Trying to figure out why the dash illumination lighting is inop. The dimmer works for the hvac, radio, prnl. I've done some poking round, all fuses are good. DTCs show codes related to communication, or loss of. Any possible common problems with this condition? I'm thinking the BCM is the problem.
 

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Discussion Starter · #10 · (Edited)
Blue Sleeve Electric blue Rectangle Machine

I have found the trouble. The wire harness extension that plugs from the fuse box under the left rear seat and the Body Control Module that mounts on the fuse panel. It's the A1 pin that is hot all the time. It is one half of the data feed + and - . The gm part number is 15077187. I've ordered a used one from Houston for $21.89 with tax. eBay.
 

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It's the A1 pin that is hot all the time
You probably already did this, but be sure nobody changed the fuse that feeds that and increased the amperage. Also may be wise to test the draw on it when you get the replacement part. (I have some of those in my spares box as I believe it is NLA)
 

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Discussion Starter · #12 · (Edited)
You probably already did this, but be sure nobody changed the fuse that feeds that and increased the amperage. Also may be wise to test the draw on it when you get the replacement part. (I have some of those in my spares box as I believe it is NLA)
Yes I did check the fuse and it is a 10 amp BUT I'm going with a 7.5 amp when I first attach this part. The part has to be changed so I ordered it. In fact I can jumper that circuit and make sure the lights work while I monitor the amp draw. Thank you very much for watching out for me. Much appreciated.
 

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Discussion Starter · #13 ·
The LEDs are as I listed previously according to the wiring diagrams.




Did you test this with a meter at the BCM??

Do you have an OBD2 Bluetooth adapter?? I am not familiar with the Snap On scanner(s) so I don't know if they will show data parameters like the dimming input the BCM is seeing and so forth. I can do this with an android app and bluetooth adapter.
I don't have a Bluetooth so I'll have to do the old fashion thing, prove out all wiring, which lead me to the wire extension wire from the fuse box to the BCM. The A1 and A2 circuits at the BCM.
Blue Sleeve Electric blue Rectangle Machine
 

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Discussion Starter · #14 ·
Lookie what I found. Got the part coming. $21.89 on eBay. I'll protect the circuit, which I've already tested using a 7.5 amp inline fuse. I have lights! My $1000 auction Envoy will be cruising at night in Mid Michigan soon. Not going to let my 2004 Ram from Texas be killed by road salt. I park it every winter.
 
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