993 Key Card Code

[Nine9six]

Can any of the 993 guru's positively identify which module is flashed with the key card code? Is it the Alarm Control Unit, the Immobilizer Unit, or is it the ECU?
Thanks in advance for your knowledge and advice.

[D_P]

When you use the code on the key card the code is ready by the immobilizer box.

A few years ago I spent some time working with an oscilloscope and data logger to try to figure out how the system works. I will try to describe the way the system works but I am going from memory that is a few years old.

There are three modules all together in the system. The immobilizer box that is a black box with mounting tabs on both sides, the motronic DME, and the alarm / central lock module.

The alarm module used in the 993 is the same module that has been in use since the 1988 928 and is used in all models through 993.

The immobilizer module is what receives the remote signal and releases the starter relay and authorizes the DME for starting.

The immobilizer and the DME are tied together via the K-Line. This is the same wire that connects to pin 7 on the diagnostic connector and eventually connects to the DME at pin 88 on 96+ models, and pin 55 on pre 96 models. The k-line from the diagnostic port goes to the immobilizer then out of the immobilizer to the DME. The wiring diagrams on these is actually intentionally vague and I had to figure this out by testing the wires. When the key is switched into the Term15 position the DME is powered on, on power up the DME transmits an immobilizer code on the K-Line, the immobilizer reads the code and transmits a different authorization code to the DME authorizing the car to start. The DME always transmits it's code on startup, but the immobilizer only transmits it's response code if the drive block has been released. The alarm / central locking module is not used at all in the authorization process and is only used to lock / unlock the doors.

When you use the code on the key card to enter the car into programming mode the code is ready by the immobilizer unit. When tuners are removing the immobilizer from the DME, they are removing the requirement for the DME to receive the authorization code from the immobilizer box. This done in conjunction with a stint replacement of the starter block relay eliminates the need for an immobilizer at all.

On the 986 and 996 the system works much the same way but they consolidated the immobilizer and the alarm functions into a single alarm box under the drivers seat. In the 9x6 the code is read from the RFID pill in the key head. Changes to the system can only be made with the factory tool and you need to have the IPAS information in order to make changes. But the system of the DME transmitting the code and receiving a code back from the alarm module remains the same.

[Nine9six]

Originally Posted by D_P

When you use the code on the key card the code is ready by the immobilizer box.

A few years ago I spent some time working with an oscilloscope and data logger to try to figure out how the system works. I will try to describe the way the system works but I am going from memory that is a few years old.

There are three modules all together in the system. The immobilizer box that is a black box with mounting tabs on both sides, the motronic DME, and the alarm / central lock module.

The alarm module used in the 993 is the same module that has been in use since the 1988 928 and is used in all models through 993.

The immobilizer module is what receives the remote signal and releases the starter relay and authorizes the DME for starting.

The immobilizer and the DME are tied together via the K-Line. This is the same wire that connects to pin 7 on the diagnostic connector and eventually connects to the DME at pin 88 on 96+ models, and pin 55 on pre 96 models. The k-line from the diagnostic port goes to the immobilizer then out of the immobilizer to the DME. The wiring diagrams on these is actually intentionally vague and I had to figure this out by testing the wires. When the key is switched into the Term15 position the DME is powered on, on power up the DME transmits an immobilizer code on the K-Line, the immobilizer reads the code and transmits a different authorization code to the DME authorizing the car to start. The DME always transmits it's code on startup, but the immobilizer only transmits it's response code if the drive block has been released. The alarm / central locking module is not used at all in the authorization process and is only used to lock / unlock the doors.

When you use the code on the key card to enter the car into programming mode the code is ready by the immobilizer unit. When tuners are removing the immobilizer from the DME, they are removing the requirement for the DME to receive the authorization code from the immobilizer box. This done in conjunction with a stint replacement of the starter block relay eliminates the need for an immobilizer at all.

On the 986 and 996 the system works much the same way but they consolidated the immobilizer and the alarm functions into a single alarm box under the drivers seat. In the 9x6 the code is read from the RFID pill in the key head. Changes to the system can only be made with the factory tool and you need to have the IPAS information in order to make changes. But the system of the DME transmitting the code and receiving a code back from the alarm module remains the same.

DP,
What a fantastically detailed description of how the system works! Thanks you so very much for taking such lengths and time in your explanation
Happy Holidays to you and your family
Best regards,
Paul