911cedric

Hello all,

i've been trying to solve a bugging issue on my 96 4S for a while with no luck.
The alarm LED is continuously ON when one or both doors are open
it doesn't matter which one. The car also unlocks itself depending on days.
Once both doors sensors are pressed, the LED turns off

I have checked both door sensors(which are basically two grounds connected to the car body), checked shorts or cut wires through the door hinges wiring harnesses, swapped the alarm computer with another one, scanned and tested the alarm system with the PST2, checked both trunk / compartment sensors, checked the central locking switch, but have found nothing relevant so far.

All the alarm sensors responded well, but i had recurrent errors codes from non plausible sensors position during alarm activation, which explains why it sometimes unlocks itself

There must be a bad ground somewhere, but where?

If any of you had a similar experience or have a suggestion please let me know
Thanks

GC96

I have no idea what is causing your problem, but you might want to start by checking the main grounding strap between the negative terminal of the battery and the chassis. I believe the original braided cable from the factory can suffer from corrosion between the wire and the crimped terminal lugs. This can result in odd electrical issues. The new replacement part from Porsche is relatively inexpensive and has a sheathing on it to prevent any moisture ingress/corrosion issues.

GC

911cedric

thanks for the suggestion but the terminals are clean and the battery new; it is definitely alarm related, there is short with a sensor or a wiring harness

hoggel

The occasional unlocking is strange. Might trouble with the central lock switch cause this? I'll verify later but I believe the switch toggles a ground input to the control unit to lock/unlock.

Edit: Sorry, I missed that you checked the central lock switch.

XavierLaFlamme

I had an issue with the switch and it caused alarm/locking/unlocking problems.
--Michael

nine9six

Curious as to where the accordion boot is that should be over all those loose door wires?

hoggel

The "non plausible sensors position during alarm activation" doesn't match any of the possible displays in the Diagnosis Manual. Could be, "Position of the drives unplausible"? Or [any of the sensors wrong] during activation?

The 'drives' refer to the door lock actuators and position switches in the door lock mechanism.

911cedric

my PST2 is set in French; i just tried to translate it into something that make sense in english
I will pull the error code / number tomorrow and see what it is in english

basically it says that doors or trunk sensors are in an odd position when activating / locking the car with the remote

911cedric

To access and check the wiring harness, i shoved the rubber boot inside the car's body;
you just have to be careful to not loosing it inside the wing panel

911cedric

i will try to swap it with a good one from another car and will see if it fixes the self unlocking issue;
however, i remember that when the central locking switch is unplugged the alarm's LED lights are not affected and are still on

What could possibly cause the self unlocking is that if one door sends a open signal because of a short circuit or defective sensor; like when you are in the car with both doors locked and that you open your door from the inside with the door
handle??

nine9six

This is telling me that one or several micro switches are out of position (need adjusting), or bad... doors, frunk, engine bay, glove box.

However, if all else is right with the system, I would have thought an error of an out of position sensor would manifest itself as a double blinking led, for having failed the system self test. Perhaps the alarm ctrl module (ACM) is bad?

911cedric

I would have loved it to be a defective alarm module, but unfortunately, it isn't.
I already exchanged with one from a healthy car with no result. Furthermore, when the alarm module is unplugged, the red led is on as always.

Also, the self unlocking problem is intermittent. I usually had to lock it twice since it used to unlock itself the first time; last week was another story, the alarm was starting to scream 15 seconds after locking, then i unplugged the battery for a night, and now it seems to work kind of normally but still the red led on

I have tested the resistance through the front trunk lock power part and it seemed to work fine. I haven't tested the different sensors with the PST2, trunk, engine compartment, doors, lights, and everything seemed responsive and normal

After thinking a bit about it, one thing i haven't checked yet is if the doors can both lock and unlock normally when using the door lock mechanism and how the LED light behaves; maybe a 964 613 134 00 microswitch has gone bad