Alarm keeps going off if key is removed from the ignition

I have a 2009 Cayman 2.9 L 6MT. Approx 49k miles, I've owned it for 2 years now. In the 2 years that I've had it, I've only put about 1,500 miles on it, 700 of which were from me driving it home from the place of purchase. My car is in excellent mechanical condition. No questionable history, etc. It was completely stock OEM everything when purchased. Overall, it has been an awesome car without any issues. During my time of ownership, I installed an aftermarket steering wheel with the appropriate airbag resistor kit (Works Bell hub kit). After the installation last summer, I did not have any airbag light on the dash at all. Everything appeared functional as normal. I also installed the Numeric shifter and shift cables last fall. There were no ill-effects after installing the Numeric shifter kit except for this annoying tick (which is a known compromise , and I don't think it is related to my question at hand). I estimate approximately 50-60 miles of driving since these two modifications were installed. I store this car in my garage during the winter with a trickle charger. I recently took her out of storage. On the third or fourth drive this year, I noticed that the airbag light came on -- this was about a week ago. There were no other issues. I haven't had the chance to do any diagnosis and review of my steering wheel installation yet unfortunately, but as I stated, I did not have any issues after the after market steering wheel was install last summer. Now today after taking the car out for a short drive, the alarm system keeps turning on when I try to remove the key from the ignition switch. The key has to be left in "on" position (one turn to the right) to keep the alarm off. Trying to remove the key will immediately cause the alarm horn to start going bonkers. Replacing the key into the ignition and turning the key clockwise once will shut off the alarm system. I currently have the main battery disconnected so that I can remove the key without the alarm going off (yes, I rolled the windows down slightly and kept the frunk unlatched). I have done some deep searching for answers, but haven't come up with anything other than possibly a dead or dying main battery or a dead or dying alarm siren battery which is apparently located under the passenger seat. I won't have any time to investigate due to work constraints for another week or two. 1. Has anyone had this happen before? Can you point me in the right direction? 2. My understanding is that the alarm system uses the main battery (frunk) as its primary power source, but also has its own battery under the passenger seat as a backup source to keep the alarm system functional in the event that the main battery dies. Given that I have the main battery disconnected and was able to remove the key without triggering the alarm system, perhaps the issue is that the backup battery for the alarm system is dead??? 3. Is the airbag light related to this issue that I am having with the alarm system? If yes, will I need to purchase a diagnostic tool such as Durametric or iCarsoft to clear this light? Thank you in advance.

Start with the main battery, especially if you're not sure of it's age or if it's older than 5 years. If it's ever been dead or jump-started, then DEFINITELY replace it. Start there, because lots of issues are caused by a low battery on these cars.

Thank you for the advice. Will start there and report back for future owners who will experience this.

When my Ford needed a new ignition switch it would continue to cause an alarm even with the key out. There’s a spring loaded button to tell the Ford wheel the ignition lock is in place, if the part is going bad, it changes the functionality of said button and the vehicle does exactly what you’re describing. So it might just need a new ignition switch.

Thank you. I did read about the ignition switch being a common issue on the 987/997, however, most people had trouble removing their key and not an alarm issue. Regardless, thank you for sharing. I think that is a good thought. Will update as soon as I get some break from work to assess.

I had the same problem. After I did the PCM upgrade for Apple car play. The alarm was always triggered after I removed the key after about 2 minutes. It turns out it was a short in one of the cables placing a load that triggers the alarm.

I would check the car for rodent damage to the wires (assuming you have already replaced the battery).

Update… Finally got the chance to take a look at the Cayman . Battery was fine, held 12.6-12.8v without charger. I listened to the horn a little more closely and it definitely was the steering wheel horn blaring and not the alarm system horn (the two are different). Turns out the connector for the wiring on the aftermarket horn button came loose and just needed to be re-tightened. Once I did this, the horn stopped going off with the key removed from the ignition. My Cayman is normal again. Whew! Love this car and the horn issue was a bit of a downer but glad it was nothing that needed significant repair. She’s a good car.

That cured the airbag light as well?

Under the seat is a sheathed wire bundle terminating at the yellow plug. Some of those wires, if cut, will trigger the airbag light. (I was installing a SmartTop module.)

Once the airbag code is thrown it will not reset itself after the fault is corrected. It must be reset by an OBD2 tool. I'm not sure if a generic code reader will do it or if it takes one with Porsche specific functionality.

A generic OBD2 tool will not reset the airbag light. You need something Porsche -specific that will talk to the computer. I have successfully used a Durametric (Enthusiast version) and more recently a Foxwell .

Just to close out this thread with a final update.... After the loose horn wiring was addressed, I have not had any more issues. I did clear the airbag light with a Porsche Durametric tool. I have not had any issues since. Moral of the story -- if you swapped your steering wheel out for an aftermarket unit and experience an issue with the horn blaring with the key being removed from the ignition, check the horn wiring/contact points.

perfact timing for this reminder! I am just waiting on a steering wheel hub adapter so I can fit my Momo Prototipo!

I strongly recommend using the Works Bell (Japan) hub as it comes with the proper wire harness adapter with built in resistors to take care of the airbag light. I spent a lot of time researching this and found that the Momo/Sparco steering wheel hub does not come with the airbag harness adapter. Some have ghetto-rigged resistors to their OEM air bag plug. I tried this initially but it’s just not worth the headache. Ended up ruining my airbag harness splicing wires etc and had to buy a new one for $90 to keep with my OEM steering wheel. The Works Bell steering wheel hub adapter from Japan is a stress-free solution to adding an aftermarket steering wheel to your 987.