Central Locking Problem: Troubleshooting Guide

Hello everyone,

'I've been having a problem with the central locking system on my 1995 Passat 35i since yesterday. When I lock the car, the central locking pump runs for about 15-20 seconds. I've already checked the cables at the door seams, and they seem to be okay. However, the car does lock afterwards. I can't read the error codes because VAG-COM doesn't seem to find the central locking control unit. Does anyone have any ideas? Surely there are multiple priority switches that need to be closed for the control unit to recognize the car as locked! Which ones would those be?'