Where does the BCM get the signal?

Hello to all,
I'm trying to troubleshoot the locking/unlocking of a 2008 Chevrolet Impala 3.5L 6cyl
Here's the problem all of the signals work except the shift out of park ( the only signal that the BCM does not see is the shifter)
So my question is does that signal come from the A/T shift lock control solenoid or does it come from the Acces wakeup serial data?
To make my question clear Where does the BCM get the signal to lock/unlock the doors once the car is in gear?
I would think A/T shift lock control solenoid because that's the only thing that makes sense to me.
Am I wrong?
Thank you for your input and time

The transmission range switch position and vehicle speed is going to be sent to the BCM via the high speed can bus.

I don't think I explained myself good enough.

I want to know where the lock/unlock signal comes from when the shifter is put into drive?

because when you shift into drive the locks should lock.

Here is a wiring diagram. I highlighted the control wires in yellow. The BCM controls the lock and unlock relays.


Do you have a scan tool to look at the BCM inputs? The lock and unlock relays are PCB relays soldered to the circuit board in the instrument panel fuse box. Looking at the BCM input data would be helpful.
Is there an option on the instrument cluster to disable this feature?
Do the locks work with the switch?

Yes, the locks work with both Key FOB and the switches but not when the shifter is put in drive when they should lock.
And I have this wiring diagram

Without looking at a complete diagram I would guess it gets its signal from the transmission range sensor

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That's a programmable feature for that car.

"Automatic Door Lock/Unlock

The automatic door lock/unlock function is a Vehicle Personalization feature with the following four programmable modes of operation:

The automatic door lock feature is disabled.
All of the doors lock when the vehicle is shifted out of Park with the ignition ON.
All of the doors lock when the vehicle is shifted out of Park with the ignition ON, and only the driver door Unlocks when the vehicle is shifted into Park.
All of the doors lock when the vehicle is shifted out of Park with the ignition ON, and all of the doors Unlock when the vehicle is shifted into Park.
The automatic door lock function can only be enabled by the body control module (BCM) if the driver door open switch and door ajar switches are in the Closed state. For information on programming the automatic door locks, refer to the owners manual."

I know all of this.
I just need to know where the BCM get the signal from to know when to use the automatic door lock feature.
As I stated before this is the only thing that doesn't work.

I imagine it has to come from the transmission range switch. Nothing else knows if the car is in park or drive.
I wasn't aware that this was a programmable feature until I read it. You made no mention of trying to enable this feature, so I thought perhaps you also were unaware...
With the doors locked, do they unlock when you put it in park?
If not, I find it doubtful that the range switch would be at fault.
If you have a scanner with data, you should be able to verify that the PCM (or bcm, TCM, cluster, whatever), recognises shifter position, thus proving circuit integrity.

What is the procedure for activating the auto lock function on that car?
All data says to refer to the owner's manual.
If this car was in my bay, I would disable then enable that function before even opening my tool box.

Just looked over the diagrams, signal does come from the range switch inside the transmission. Goes to the transmission module, which goes out over the network.

Tyler wrote: Just looked over the diagrams, the signal does come from the range switch inside the transmission. Goes to the transmission module, which goes out over the network.

So are you talking about the acc wakeup data line?
Because I was thinking that or the A/T shift lock solenoid.

Ok, I think I see where the signal comes from now which is the hi-speed data line from the transmission module.

just wanted to make sure my thinking is right.

I don't want to waste too much time when I do get the car which will be the end of this month.

Am I right??
If I'm right I want to thank you all for your help.

Albee9 wrote:

Tyler wrote: Just looked over the diagrams, the signal does come from the range switch inside the transmission. Goes to the transmission module, which goes out over the network.

So are you talking about the acc wakeup data line?
Because I was thinking that or the A/T shift lock solenoid.

Ok, I think I see where the signal comes from now which is the hi-speed data line from the transmission module.

just wanted to make sure my thinking is right.

I don't want to waste too much time when I do get the car which will be the end of this month.

Am I right??
If I'm right I want to thank you all for your help.

Your thinking is right! Pretty sure it gets that data from the high speed network, and not the wake up line or the solenoid.

Tyler wrote:

Albee9 wrote:

Tyler wrote: Just looked over the diagrams, the signal does come from the range switch inside the transmission. Goes to the transmission module, which goes out over the network.

So are you talking about the acc wakeup data line?
Because I was thinking that or the A/T shift lock solenoid.

Ok, I think I see where the signal comes from now which is the hi-speed data line from the transmission module.

just wanted to make sure my thinking is right.

I don't want to waste too much time when I do get the car which will be the end of this month.

Am I right??
If I'm right I want to thank you all for your help.

Your thinking is right! Pretty sure it gets that data from the high speed network, and not the wake up line or the solenoid.

Thank you.
I see what I was doing wrong didn't look at everything that was involved with the circuit.
Thank you for pointing that out