Brake Light Switch Circut Issues

[TheJohnGaltLine]

Hello, long time lurker, first time poster. Hope everyone is having a great day. Thanks in advance for even reading this post.
Also, thanks for the years of knowledge I've siphoned from here over the years .

Short Version: Strange circuit issues.
I have a 2005 Volvo XC90 V8. It's my pregnant wife's vehicle and she loves it (I love my 93' 244 better). It has been a reliable vehicle up until the last month. I'm not able to shift out of park with car running and I also have no brake lights. I replaced Brake light switch and that did not work. Replaced all fuses, checked all bulbs, tested switch and everything checks out. Only code is BCM-C004064

I started circuit testing using a wiring diagram and found something strange that I can't explain. Maybe one of you have run into it. I tried to organize the information as best I could.

This is per wiring diagram:
CEM Fuse 9
Receiving 12v
B:11 Red wire from CEM to Brake Light Switch Pedal not depressed
Receiving 12v.
B:11 Red wire from CEM to Brake Light Switch Pedal depressed
+-.3 mv.
C:34 Yellow/Red wire From Brake light switch to CEM
+-.3 mv regardless of pedal status.

Strangely it seems when the pedal is depressed, both wires go essentially dead.

Brake Light Switch resistance closed:
.3ohm
Brake Light Switch resistance open:
Infinite

My next step when its light out tomorrow is to try checking continuity on C34 between the CEM and the Brake Light Switch (as much as I don't want to pull it apart).

I normally am pretty good at figuring things out, but this has me stumped as to why the voltage is just straight up disappearing. It is almost like something is cancelling it out.

--

Below is additional information regarding what I've tried so far.

Once started the vehicle will not move out of park as the solenoid at the front of the shifter assembly is staying powered on.
It starts fine, runs fine, drives fine if you start it in neutral and go to Drive or Reverse.
The Brake lights do not function at all when stepping on the pedal (including the high mount brake light).
Using the stop light activate option I can make the High Brake light come on, but the low mounted lights remain off.

Status upon Pressing in Brake Pedal
Pressure Sensor Status - Active
Brake Light Switch - Not Active

BCM - 1 Code
CEM - No Code
DEM - No Code
REM - No Code

The Volvo DTC coming up is BCM-C004064
Brake Pedal Switch "A" Algorithm Base Failures. Signal Plausibility Failure.

Testing the Brake Light Switch out of car directly off a battery shows 12v through it when closed.

[ggleavitt]

Given all that you've validated thus far, I might check the CEM then REM. Between the shift interlock and brake light oddities, you have two active modules involved. REM (F:4/F:5 top, B:3 sides) manages the brake lights using instruction sent by CEM (LS CAN bus I think, not LIN?). CEM (fuse F9, pins B:11, C:34) manages the shift interlock on the gear selector. This is MY05 so older style cover over CEM, has the potential to leak. REM usually doesn't make too much of a fuss but it does have separate electrical connections to side and top lights so oddities between the two would come from there.

I'm guessing the brake switch is okay, something else might be at fault or you could have two separate but unrelated issues, but both have CEM as part of the logical path and that's a good place to start. You can pull the cover under the driver's side windshield screen or get up under the dash and look closely at the module. With battery disconnected (wait 5 min after turning vehicle off for modules to write out), see how far you can get removing the CEM-and checking the top, that's probably where you'll find issues if there are any.

Might be something completely different but this is where I would be looking next as based on what you've noted to date.