Was doing some research on my same issue and came about this thread. Just though I'd post that, after having mine work very intermittently recently (worked 25% of the time?), I took it apart, pulled the battery, unsoldered the battery case, retouched all the solder joints with just tiny bit of flux and solder, and now it's back to working beautifully again. Took about 5 minutes. (Note that I'm an experienced solderer and have a fine tip on my iron for small parts like that.). I bet this is the problem with most of them.

 

This can be done...

 

Tried everything and did the reverse polarity last and it worked. my fob is beat to craps but it's still ticking.

 

Call these guys and see if they can help if it acts up again. They just rebuilt a key fob on my 993 while they were rebuilding my immobilizer. Looks like they work on 996s too.

http://www.ecudoctors.com/porsche-996-2000-2004.html

 

These are RF transmitters. In my professional photography work I use them to trigger remote flashes. What I learned is that the radios are very sensitive to the battery voltage. Be sure to try a brand new fresh battery. In my case, the battery showed almost 3V on a meter, and flashed the little LEDs in the key fob but would not trigger the radio. When I replaced it with a new one, everything worked. Good luck.

 

I've never seen anyone post info regarding recovering the 24 digit code (any fashion or via PIWIS) that comes on the original key head.

 

PST1/2/PIWIS I/II/III all display a portion of the code to identify the remotes, I did read once someone found the entire hex code but didn't look into it any further but I am curious about it.

 

So, I have a 997.1 TT (2007) with PCM, Sport Chrono and Tiptronic (who knows, that may matter for this subject). Saturday morning I went to garage to head out for a drive and the key remote would not open the door. I had driven it less than a week prior to this so I knew it was not in hibernation mode. So, I unlocked the door manually, put the key in and turned it to disable the alarm. Then took key out, shut the door from outside and it still did not lock/unlock the door. Thus, changed the battery. Still nothing. Red LED on key fob was working before new battery and after. Maybe the battery I replaced was bad, maybe not as the LED does not take much power as has been said. The day before I had key in my pocket all day and with what I was doing probably caused the buttons to be pressed a lot and maybe stay pressed (we all are familiar, I am sure, with sitting down with 997.1 key in your pocket and your front lid pops open). By the way, the key would start the car. Anyway, I went and got the other key and it would unlock and lock the car so I knew it was the key. Enough of that for the time being, I went on my drive bringing the extra key with me. Last night I did some research and found this post and some others. I did everything on https://rennlist.com/how-tos/a/porsc...working-377643 and nothing, ideas from other posts too. I tried pressing the buttons with key next to door key slot as the manual suggests. I also put the key in the door, held the button and unlocked and locked. Nothing worked. Today I got in the car and tried the re-sync (step 3 in link above). That did not work. I closed the door and this time I put the key in (I cannot remember if I was holding the button down when I put the key in or after I put it in). With the button pressed, I turned the key to the first stage to turn on the instrument cluster and let key come back. I never let go of the button and held it for 10 to 20 seconds. I do not recall any light on the dash illuminating. After that I pulled the key out and pressed the button. The door locked! I unlocked it with the remote, locked and unlocked it again then got out and locked/unlocked again. The remote was again working as it should. Hallelujah! I did not find the process I stumbled across that worked for me written anywhere so figured I needed to create an account and post this. Hope it helps someone sometime. Cheers!

 

I had a very similar experience with my VW Passat wagon… it was after the battery had died in my spare key (I had misplaced my regular keys). I replaced the battery but the remote still wouldn’t unlock the car. Fortunately, I also found the “hidden secret key” in the key fob which let me unlock and use the car (once the fob was in the ignition everything worked). The remote still wouldn’t lock/unlock the doors though… In the meantime, I found my “lost” keys (I had left them in a different coat that I hung behind a door and promptly forgot about). Once I used my “regular” keys, everything worked/works fine with the spare set again…

 

What do you mean you "let key come back"???

 

I’ll go test so I can better explain it or correct what I wrote.

 

I tried a number of variations like that and none worked. Good that you had some joy with your key.

 

So, I tested this morning. The key in the 997.1 TT has 4 positions, let’s call them P-1, P0, P1 and P2. When you insert the key it is at P0. After you move it to P1 (powers on car accessories) or past P1 to P2 to start engine key goes back to P0. After you have moved it to P1 or P2 and is has returned to P0 you cannot remove the key until you move it to P-1 which turns off accessories and/or engine, then it returns back to P0. At that point you can take the key out. Thus, unless you are physically turning the key, the key returns/springs back to P0. So, when I fixed my remote the other day, I put the key in (either with the button pressed as it went in or after it was in) and, with the lock/unlock button pressed, turned the key to P2 (without the brake pressed so engine did not start) and held it there for 10 to 20 seconds. Again, I do not recall whether any light on the dash illuminated. I then turned the key to P0 then P-1 (I cannot recall if i let go of the button or not when I turned it to P-1) and removed the key after it returned to P0. I did not have the button pressed by then but when I pressed button on key the doors locked. I pressed button again to unlock and got out, closed the door and locking/unlocking with the remote was again back functioning as it should be. I hope that adds more clarity.

 

Yes, that "re-sync's" the key.....

Later 996's and 997's have a "Megamos Encrypto Secret Rolling Code" in the Transponder and Immobilizer that changes every time the key is turned on....

If the key has been in your pocket and the buttons get pressed a lot accidentally while not near the car, the key can get out of sync....

What you did re-sync'd the key to the Security System.....there is an official procedure but is pretty much what you did and I can't remember it verbatim...

 

Good info! Thank you.