I can't get the back seat off to check the BCM, is the a trick to it? Do I have to access it through the trunk? Any help would be appreciated.
I've got the bottom seat out but can't figure out the back rest. I tried going at it from the trunk but the nuts holding the black plastic casing don't want to move. I'm losing patience with this freakin seat. Do I even need to remove the backrest or is the BCM on that black plastic casing/or accessed with it out of the way?
It is accessible once removing the rear seat back rest.
Normally should be accessible from inside the vehicle but the plastic tray housing the rear electronics bay components can be unclamped once the seat rest top screws are removed (plus 2 more for the tray). It can be flipped down into the trunk, the wires are long enough to allow the movement. But again the tray is meant to be accessed from the inside the vehicle.
The '98+ gen V design with DIM and RIM (the equivalent of PZM in gen IV) was intended for long time.
Before use to be called Body Control Module (BCM) but it took too may wires to run from the various places in the vehicle all the way to the BCM. So they idea was let's split it in more localized modules having just 1 wire (data line) in between.
The PZM was renamed before actually being split and funny enough once split it was renamed again to Rear Integration Module (deals with controls located in the rear side of the body) and Dash Integration Module (dealing mostly with the front side of the body).
There ared few modules with an interesting name/history:
"PCM" - Powertrain Control Module (not just ECM) as it deals with the transmission too.
"RIM" - Radio Integration Module up to '95 accurate terminology, later on '96-'97 (Seville, -'99 Deville, -'02 Eldorado) was incorrect as the module function was a Sound Processing Module (not dealing at all with the Radio). In gen V it was renamed AMP when the name kind of became again not very accurate (AMP is one of the functions, it also includes the sound processing earlier functions).
RIM vs RIM (Radio Integration Module vs. Rear Integration Module) confusion with gen IV and gen V Seville, further more up to '02 same module (RIM) had different meaning in different models.
Back to PZM/DIM/RIM, well gen IV PZM+IPC functions were spread in between IPC+DIM+RIM (mainly IPC lost some of its functions to the DIM).
Generally since they started adding electronics to the vehicles the trend was towards integration (lesser modules/more functions in one module), with the exception of the body functions where the current was to create zonal modules (rather than per function modules).
The goal is cost reduction, weight reductions (lesser wires), faster assembly times.