2001 Cab Alarm Fault - And it's not the radio ground.

This is a bit of a puzzle, for all you expert diagnosticians out there. Pretty much since I have owned it (since 2012), my 2001 996 Cab C2 has intermittently emitted a short, single beep upon locking with the remote. I might get two or three successive lockings with no beep, but then the beep returns. The owner's manual lists two conditions that could cause this single beep: 1. If not all alarm contacts are closed (doors, boot, bonnet, radio, console glovebox), and 2. Locking twice with the remote. I am not in the habit of pressing the lock button twice, so I discount the second condition, which means it's the first. (Please don't ask if the radio is original or aftermarket. Yes, it is, but the problem existed before the radio was replaced. And if it were the radio ground making contact, it would not be intermittent.) That leaves me with doors, boot, bonnet, and glovebox. I have talked to several service advisers and technicians, and they are no help. I've been dealing with this for 13 years, so here I am, appealing to all and sundry for some insight into the alarm system, door operation, and wiring. It seems to me that this has to be caused by a fault in whatever sensor(s) or switch(es) the car uses to determine the position of doors, boot, bonnet, and glovebox. There is a warning light for the boot/bonnet not being latched, and as I don't see this intermittently flashing at me as I drive, I discount those. There is no "door ajar" warning light (how the Germans overlooked that, I do not know) but I believe that if the problem was in one of the door handle/locking mechanisms, other things intermittently wouldn't work, such as the window drop, and that works all the time. If my reasoning here is accurate, that means it must be the glovebox. This weekend, I removed the panel with the window switches from the console and stuck my hand in to manipulate the wire lead to the glovebox microswitch, mainly because I had run out of ideas. And bingo, no alarm beep! I could repeatedly lock and unlock with no beep. Except that 10 minutes later, wire lead undisturbed and car otherwise untouched and unmoved, it was single-beeping upon lock again. I removed the console and replaced the 10 or 12 inches of wiring from the wiring harness bundle to the microswitch (I left a two-inch stub at the harness to attach the new lead). No beep! Except that 10 minutes later...I was back to square one. (BTW, I did establish that the hot wire in the original lead exhibited at least a partial current leak through the insulation.) I am stumped, flummoxed, defeated. That wiring harness has about 40 wires and it disappears under the gearshift just after the microswitch lead disappears into it. Why would manipulating the wire lead and replacing the wire lead bring about only a temporary reprieve? Is the problem really in the wiring? Is the problem really in the glovebox? Do I have the only 996 in the world that does this? Is it really condition #1, or is my keyfob somehow sending a double lock signal?

Quotes source post: 20171236

Could be an intermittently functioning micro switch and not the wiring..? Could jump out the micro switch wiring thus eliminating the micro switch from the equation and see if that makes any difference in beeps..?

Quotes source post: 20171346

Removing the console means the microswitch gets disconnected,so it is out of the loop. As with the radio ground, the "safe" position for the doors, boot, bonnet, and glovebox is with the switch open. Switch closed (or a ground fault) equates to not safe, causing the fault. When the glove box is closed, the microswitch should be open. Unplugging the microswitch makes the alarm system think it is safe.

Chased an immobilizer issue for 6 months with the car not locking. Turns out the unit had bad solder tracks. Ecudocots in fl was able to fix it. Thet can diag the units so u stop chasing your tail. Also a piwis system or better scanner will read the alarm modual and tell u the fualt code.

I should add that there have been no error codes in the system, at least according to the dealer.

And a new update: Knowing that troubleshooting like this can be thwarted by false assumptions and keeping in mind Sherlock Holmes (“When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth”), I dug out my other keyfob. This would be a brand-new one I had made last year to replace a lost fob. Never used. Lock with the old fob: beep. Lock with the new fob: no beep. Lock with the old fob: beep. Lock with the new fob: no beep. Could it be possible that the old fob is emitted a double signal?

I uiess anything is possible. I had no codes either thats why mine was so hard to diag. If u get tired of chasing your tail send it out for testing.

As I understand it, a "closed" switch is not an error. As far as the alarm is concerned, all these alarms points (doors, lids, radio, glovebox) have only two conditions: safe (switch open) or unsafe (switch closed). The beep is simply the system alerting you to a condition that may not be intended by you.

My .002c The double press of the Fob turns off the "interior monitor" so you can leave a dog in the car and he will not set off the Alarm while you run into a Store... If you have 1 Fob the is strangely accidentally doing this you can test it out by locking the car,( windows partialy down) then trying to set off the Interior Monitor to verify whether this is actually the case... another thought....you are chasing your *** with this complicated system and not even having a PIWIS to help you.....Yes it my give a lot of conversation ( if thats what you want).. but to truly get to the root of the issue the PIWIS will eliminate 90% of the wrong assumptions and the conversations and testing of them.

Quotes source post: 20172198

Worth at least 20 cents, that. Good suggestion on checking out to see if the infrared sensor is active or not. That will resolve the key question (see what I did there?). Of course, the infrared sensor is deactivated if the top is down; what about the windows? Ah, never mind. I just thought of a better way. I can put my wife in there and lock her in. I don't know how much a PIWIS costs, but I am not going to invest in a PIWIS. Mainly because I am selling this car. However, as it is always possible that I will buy another Porsche someday, can you explain for me how PIWIS would identify the cause if the cause is not a fault in the system but rather what I originally concluded was basically a ground fault? I know nothing about PIWIS other than it has a funny sounding name. Of course, if PIWIS could have provided an answer, then I guess I need to ask my dealer and my indy shop why they didn't find the source of the problem?

Okay. With a passenger in the compartment and the top up and windows closed, I tried both keys. The old key elicited a beep, and the alarm system did not react to the passenger inside. The new key did not elicit a beep, and the alarm system did not react to the passenger inside. Same result. Brand new infrared sensor, btw. Replaced it in May of this year hoping it was the problem. Thinking it might require some time for the sensor to detect the body heat and realizing that I could very well sit in the car myself and do this, I released my wife and took her place in the car. Locked myself in with the new key. No beep, but also no reaction from the alarm system, even after four or five minutes. Anyone have any idea how long it should take the infrared sensor to determine a warm body is in the passenger compartment?

I think the Interior Monitor picks up "movement" not "body heat" ....try the test again but don't just sit there... I think the Alarm System will " Arm"even with windows down and/or Top down on Cabs, so that if someone reaches in to grab someting off the seat it will set off the Alarm... Again, you really need a PWIS to Toubleshoot this system...You can get a cheap clone by following these links.. https://rennlist.com/forums/996-foru...ighlight=PIWIS

With the piwis u can activate each individual alarm action 1 at a time and verify if they r working seperately.