Looking for a Porsche Tech for a Question about Keys

[rich]

Anyone on here a Porsche Tech or dealership wrench? Send me a pm. I have a strange question about ignition keys.

TIA

[Wayne 962]

Post your question here, I know how to cut and code keys for both the alarm and the ignition.

-Wayne

[WRGREENER]

wayne, would you be willing to share the process, details, sequencing, and general mechanism of how the coding is accomplished? there seems to be a lot of "mystery" about key coding. e.g. key in ignition vs out, serial numbers or not, part numbers or not. and, then you say you know how...does that mean you will offer as a service?

[eric523]

key in, serial numbers yes

[rich]

Yep, lots of mystery surounding the key and how it works. What part of the electrical system talks to the key? The ECM?

[eric523]

Originally Posted by rich

Yep, lots of mystery surounding the key and how it works. What part of the electrical system talks to the key? The ECM?

Key talks to the immobilizer.

There are two main electrical portions of the key. The cicuit board that controls keyless entry and alarm, and the pill that must be present or the bladed key will not start the car.
I don't know of a way to program keys without the Porsche Systems Tester.

In order to program a key with the systems tester, you need the cars immobilizer code that you get from the dealer by VIN, and the keyhead's 22 digit serial number.

[rich]

Are all late model Porsche keys physically the same? I mean would a key blank for a Boxster, 911, Cayenne all slide into each others ignition switch?

[eric523]

No they are not all the same. The 996 and 986 key blade portions are the same. The remotes/keyheads are different for different models and years.

Cayenne's are different entirely because they use the VW switchblade style.

[eric523]

know that not just any key place can cut the blanks either. The Porsche keys take a special cutting machine.

[rich]

So if a guy was to change engines would you be able to use the ECU from another car?

The transponder doesn't talk to the ECU right?

[eric523]

you would have to be more specific. Same size engine? same year?

ECU is most commonly referred to as DME within the industry now. Which is different from the immobilizer that deals with alarm and keys.
DME runs the motor, but only if the immobilizer lets it. If your key and immobilizer aren't happy, it will not start the motor.

There is aftermarket DME software out there that can actually eliminate the need for an immobilizer at all. If you're doing a swap to a bigger motor and removing emissions equipment for a track car or something, I would definitely just remove the immobilizer all together. And actually remove the keys and steering locks as well and just use switches.

If you simply put the same size/year engine in the car, both the DME and Immobilizer and keys should be unaffected.

[rich]

Thanks for the response. Hmmm.. Ya, the DME. so, if the car no longer has the key and the immobilizer you could light the DME with a hot wire from a toggle switch, add a push button for the starter and crank up the engine?

So the key doesn't talk to the DME just the immobilizer.

[eric523]

In my race car(immobilizer system removed), I have a power switch that basically turns ignition/dme on(same as turning key into ON position), and a starter switch(that engages starter).

stock car:
Yeah, basically the keys programming portion talks to the immobilizer.

The DME just relies on the key actually turning the ignition on and starter engagement. But the DME will not fire the car unless it gets the OK from the immobilizer...even if the key blade is correct and turns in the ignition housing.

[rich]

Originally Posted by eric523

In my race car(immobilizer system removed), I have a power switch that basically turns ignition/dme on(same as turning key into ON position), and a starter switch(that engages starter).

stock car:
Yeah, basically the keys programming portion talks to the immobilizer.

The DME just relies on the key actually turning the ignition on and starter engagement. But the DME will not fire the car unless it gets the OK from the immobilizer...even if the key blade is correct and turns in the ignition housing.

OK, got it! Cool, So, the key chip turns on the immobilizer allowing the power to pass though the immobilizer to the DME and starter. Got it! Thanks!

So in swapping engines or buying a car without an engine I just need to be sure to get the DME for the engine I'm installing. Sound right?

[eric523]

Yep sounds like you got it.


Not all DME's work for all engines, so you can check Wayne's book/list for compatible units. If you buy a 2.5L car that has an immobilizer and DME already in it, you just need a 2.5L engine and you're set. You don't necessarily need the DME and immobilizer from the new engine. The new engine with harness should just plug into the existing harness.

[Wayne 962]

So to answer the question from a few posts ago, programming keys is not an easy process. I don't remember the exact procedure, as I need to have the PST-2 open and in front of me, so I can remember 100%, but I'll do my best here.

Each key contains two separate "electronic circuits" that interface with two separate modules in the car.

Firstly, you do need a PST-2 to plug into the car. Secondly, you need to know the codes from the key for both the alarm module and the DME. You program the key codes into the alarm module so that when you press the button on the key, it will open the doors. I believe that there are two spots in the alarm programming module that you have to enter the codes. Note that if you program the key only to the alarm module, then you can open the car with the button on the key, but you will not be able to start the car (this stumped me a ways back when I was first messing around with it).

Secondly, you need to enter the RFID immobilizer codes into the DME section using the PST-2 so that the key will be able to start the car. You need to obtain from the dealer, the DME access code that will allow you to program your car (they look it up in a big database). Then you enter the codes into a spot in the PST-2. I believe you can have up to four keys programmed at a time.

Finally, you need to actually take the blank key to a dealer and have them cut the pattern for the car. Apparently, these key cutting machines are not at every dealer - the only one around here in the South Bay was at the Audi dealer - I had to sit there and wait almost 45 minutes while someone disappeared into the back room and figured out how to use the machine.

In all, it was a total pain in the ass, and that's with having all of the tools to do it. If you randomly purchase a key off of eBay, then that key is worthless without the code that typically comes attached to the key. For reference, when you purchase a new blank key from Porsche, it comes with a tag with the codes listed on it. Here is a photo of what it looks like:



-Wayne

[enthuz]

In searching for key info I found this thread and have another question for the experts. A friend who is an X Porsche owner mentioned that the battery in the key head gets recharged, like an electric toothbrush, when the key is in the ignition. I have a new spare key that won't get much use, so do I need to use it more often to keep it charged?

[Wayne 962]

Originally Posted by enthuz

In searching for key info I found this thread and have another question for the experts. A friend who is an X Porsche owner mentioned that the battery in the key head gets recharged, like an electric toothbrush, when the key is in the ignition. I have a new spare key that won't get much use, so do I need to use it more often to keep it charged?

Not really. What he probably means is that there is an RFID chip inside the key that gets read when the ignition is turned on. This has a tiny little capacitor in it that temporarily charges the circuit inside so that it can transmit its code to the car. He might be thinking of that as a "battery".

Info from wikipedia page: Radio-frequency identification - Wikipedia, the free encyclopedia

A radio-frequency identification system involves hardware known as interrogators or readers and tags, also known as labels, as well as RFID software or RFID middleware.

The tag's information is stored electronically. The RFID tag includes a small RF transmitter and receiver. An RFID reader transmits an encoded radio signal to interrogate the tag. The tag receives the message and responds with its identification information. This may be only a unique tag serial number, or may be product-related information such as a stock number, lot or batch number, production date, or other specific information.

Many RFID tags do not need a battery, which makes them cheaper and smaller. Instead, the tag uses the radio energy transmitted by the reader as its energy source. The interrogator must be close for RF field to be high enough to transfer enough power to the tag. Since tags have individual serial numbers, the RFID system design can discriminate several tags that might be within the range of the RFID reader.

RFID tags can be either passive, active or battery assisted passive. Passive RFID does not use a battery, while an active has an on-board battery that always broadcasts or beacons its signal. A battery assisted passive (BAP) has a small battery on board that is activated when in the presence of a RFID reader.

Tags may either be read-only, having a factory-assigned serial number that is used as a key into a database, or may be read/write, where object-specific data can be written into the tag by the system user.

RFID tags contain at least two parts: an integrated circuit for storing and processing information, modulating and demodulating a radio-frequency (RF) signal, and other specialized functions; and an antenna for receiving and transmitting the signal.

Fixed readers are set up to create a specific interrogation zone which can be tightly controlled. This allows a highly defined reading area for when tags go in and out of the interrogation zone. Mobile readers may be include thosetaht are hand-held or mounted on carts or vehicles.

[enthuz]

Wayne, thank you very much for the detailed answer.

[bsherrard]

Wayne - you mentionted in your excellent write up that the key needs to be programmed to be able to unlock the doors. a few weeks ago my key stopped unlocking the doors & trunk. Of course I can open the car by using the key in the lock but the transmitter won't work. I replaced the battery but that did not fix it. Do I need to take the car & key to a dealer to get it re-programmed? Why would it "lose" its program?
thanks for any help.