door lockING (Early 95) - quick reference
Before mid-1995, Porsche 993 door locking and unlocking was performed using the physical key inserted into the door lock cylinder. When the key was turned, a switch inside the cylinder momentarily grounded either the "prime" (lock/arm) or "unprime" (unlock/disarm) input line of the Alarm Control Unit (ACU), depending on the direction of rotation. In response, the ACU sent power to the door lock actuators, causing them to either engage or release the locks. Simultaneously, the ACU armed or disarmed the alarm system accordingly.
To ensure proper function, the system employed limit switches inside the actuators. These switches confirmed whether or not the lock mechanism had fully moved to the locked or unlocked position, providing essential feedback to the ACU. More detail
door locking (Early 95) - Detailed
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door locking (Late 95 - 98) - quick reference
In mid-1995, Porsche introduced the Drive Block system, which enhanced security and added remote lock/ unlock capability. This upgrade replaced the earlier method of using mechanical cylinder lock switches to ground specific inputs to the Alarm Control Unit (ACU) based on key rotation.
With the Drive Block system, a dedicated immobilizer module communicates directly with a radio frequency key fob. When the fob is pressed, a secure RF signal is transmitted to the immobilizer, which decodes the request and sends a corresponding lock or unlock pulse to the ACU. The ACU, in turn, activates the door lock actuators and either arms or disarms the alarm system. The immobilizer only responds to fobs that have been "paired" to the immobilizer.
As can be seen in the diagram below, although the method of initiating the command changed—from physical key rotation to RF signal—the downstream behavior of the ACU remains largely the same as in earlier 1995 models. Feedback from limit switches within the actuators is still used to verify lock position More detail.
door locking (Late 95 - 98) - detailed
