CarcentricB

Hi,

I have a '95 993 RoW OBD1 with an aftermarket alarm on top of the Porsche Alarm and Immobilizer. The aftermarket alarm was installed in such a way that the Immobilizer functionality has been removed (I no longer need the Porsche fobs, only the aftermarket fob).

I checked the DME and it has never been opened, so the chip was not replaced with a 'non-immobilizer' chip. I also opened the Immobilizer unit to see if it has been changed inside but it looks original.

I know that several posts on Rennlist state that the Immobilizer functionality can only be removed with a non-immobilizer chip in the DME and with a change to the Starter relay (or installation of a simpler jumper relay), but this doesn't seem to be the case for my 993!? So I'm really puzzled...

Could it be that the earlier ('94 and '95) and/or Euro 993's don't have the complex interworking between the Immobilizer and the DME that is described in other articles (like the K and L line 'coded' communication).

If I look at the '95 wiring diagrams, the Immobilizer primes/unprimes the Porsche Alarm Control Unit which then feeds the DME with a Term15 signal (which the DME then uses to activate the DME Relay I assume). The Immobilizer also activates the R61 Starter Relay of course.

What if an aftermarket alarm just takes a Term15 (for instance from the Porsche Alarm Control Unit's pin 4) to directly activate the DME Relay (pin 4 on the ACU black connector is Term15 normally going to the DME). The Starter relay can also be activated directly by an aftermarket alarm or it can just be jumped(numerous posts about this on Rennlist).

Wouldn't this work to remove the Immobilizer functionality in a simple way (maybe only for '95 RoW's...) ?

If this topic is too sensitive to talk about in this forum, can someone who knows more about this please pm me ?

Thanks!

nine9six

Are you sure your car was equipped with an immobilizer? Some early 95's with OBD I were produced without the immobilizer; or maybe it was an upgrade you could purchase in early 95. I understand all later cars after a certain build date, came equipped with the stinkin immobilicer unit.

ble2011

I have a '95. When I bought it, it had an aftermarket remote locking fob. I'm not sure if it had the immobilizer or not. When I redid the stereo, I had a wire that had a tag with alarm printed in it, but it's no longer connected to the stereo or anything. I also have the lights on top of the doors that blink when I lock. Everything seems to work without any fuss, so I just left well enough alone.

CarcentricB

@nine9six : yes, I'm 100% sure I have an immobilizer. In early 993's it was an option (M530). My Immobilizer is a 993.618.159.01 and I still have the original Porsche fobs that came with it.

@ble2011 : you can easily check if you have an immobilizer: it's under the driver's seat next to the DME. Don't worry about the alarm wire for the radio (the green wire), it can be left unconnected. If you're happy with the aftermarket alarm, I would indeed leave it in. I have to replace it or reactivate the Immobilizer since the manufacturer of the aftermarket alarm is out of business, I only have one aftermarket fob left, and I have no alarm code for it.

But first I need to figure out how my current setup works...

ToreB

This is interesting. I would guess that all cars fitted with M530 will be alike, thus the mobilizer interruption of several signals from/to the DME.
However, the schematics on M530 are not complete, and I suspect that several connections are not part of the documentation.
Cheers,
Tore

1stgear

My car was the same way when I got it. I made the mistake of having the alarm removed. The shop then had to spend 3 days figuring out how to get the immobilizer to function properly again. Not fun and not cheap.

CarcentricB

Hi Tore, the Term15 feed from the Alarm Control Unit to the DME is also going to the Immobilizer.
So a possible explanation could be that when the Immobilizer receives the Term15 it no longer blocks the several signals from/to the DME.

This is more or less where I am now: some of the aftermarket alarm connections can be bridged (as if it is no longer there) but then the Immobilizer doesn't seem to resume its original functions.

So I first need to figure out how the original Immobilizer functionality was removed to be able to restore it...