Electrical issues

[dblover1327]

I got a 2003 chevy tahoe and i have some electrical issue. I know one of them is the bcm since my windows don't work and as soon as i plug a new bcm into it my windows work. Now Idk why My night lights turn on when i turn on my car and the daytime don't want to turn on. When I have the perimeter lighting on, the daytime lights do turn on but not when i start my car it goes straight to the night light. Second problem I have the rear access door message and need to find the wire at the bcm and disable it so i can run a new wire to the back since the wire is grounding somewhere. It drains my battery over night eh and my alarm won't arm since it think the rear hatch is still open

 

[dblover1327]

bump need some help

 

[dblover1327]

Bump need the help lol

 

[dblover1327]

bump

 

[OmarR]

You are having all these problems with the new BCM?

 

[dblover1327]

Old and new. With the new ones it's the rear access and daylight lights

 

[OmarR]

So...

Old BCM = window problems, no other problems.
New BCM = windows fixed, but now rear access and DRL problem?

I would post up both BCM part numbers to see if they are compatible. For example, you may have a 2003 BCM, but it could be for a Silverado, so it doesn't know how to interpret a rear access signal. But that's just a guess. If you didn't have rear acces & DRL problems with the first BCM, then I doubt it's a wiring issue.

Is the 2nd BCM used? Part numbers could be the same across a span of trucks (Tahoe, Yukon Denali, Silverado), but the software programming could be different due to the different level options of the truck.

This is why when you look at BCM's on ebay, reputable vendors (usually high-profile junkyards) will also post the VIN of the donor truck and all the options that they are aware of .

 

[dblover1327]

My bad on not making sense. With old bcm I got rear access door, rear windows not working and day time lights. with new one my day time lights don't work and get the same message about rear access.

 

[dblover1327]

bump for help

 

[dblover1327]

Bump

 

[rob71]

The BCM door ajar inputs are:
cargo door/liftgate switch is pin A1 (pink/black wire) on Connector C6 (the purple plug)
right rear door is pin A2 (light green/black wire) on C6
left rear door is pin A3 (light blue/black wire) on C6
just for your information, the front door switches are via class 2 serial data from the front door modules (ie. the front door switches are not directly connected to the BCM).

Anyhow, these switch inputs will be grounded when each door is open. If you see that one of the door inputs is always grounded no matter if the door is open or closed then you'll want to look at the wiring and the door switches. If you don't find that one of the inputs is stuck to ground, then that suggests a problem with the BCM.

I would guess that the light problem might be the wiring to the light sensor that's supposed to tell the BCM that it's dark or light out. I'm not sure how to test the sensor. According the diagram the sensor is a phototransistor, with one side connected to ground at the BCM (black wire at pin B7 on BCM connector C4, the light blue 24 pin plug), and the other side connected to an input on the BCM (white wire at pin A4 on BCM C3, the 24 pin brown plug). The voltage at the white wire should change depending on whether the sensor is seeing daylight or darkness. You will need a good voltmeter or DMM to test that input. If the white wire always has 5V on it, that suggest that the ground wire to the light sensor is broken.

Hope that's of some help.

 

[dblover1327]

Thanks for the help!!