chip inside ignition key
 

My ignition key has fallen apart. It broke a while back and I had it taped together awaiting another key. The other day it fell apart completely and I can't find the computer chip that's inside the key. I know when and where it fell apart and I looked outside the car and didn't see it so, I assume it's under the seat somewhere. The car still starts and everything works besides the keyless entry.

I have heard that if that chip isn't in the car, the car will not start. Is this true? Or is it strictly used for the keyless entry?

My understanding is that the key has an immobilizer chip that must be near the ignition. If the car doesn't get the chip signal when the key is turned the car is immobilized and can only be undone by the dealer.

The 'chip' is technically a transponder coil, more specifically a magnetic-coupled transponder coil, basically meaning that is has a non-volatile memory and does not need it's own electrical energy to operate. Since it has no power of it's own, it's range is very limited - usually 0.3"- 6.0".

When the actual key is inserted into the ignition lock and turned to position '1' or '2', an induction coil that is mounted around the ignition lock is energized and sends out an electromagnetic field of energy. The windings in the transponder chip absorb that energy and power the electronic chip to emit a signal.

The induction coil around the ignition receives the signal and sends it to the DME for recognition. If the signal is recognized as being already in the DME’s memory, the signal is accepted and the vehicle is 'allowed' to start.

Proximity is the key here, your 'chip' must lie within the range described. This will give you a clue as to where to look for it. Having some magnetic components in it, you should be able to find it using a magnet passed slowly, and closely, over the carpet. The chip should be attracted to the magnet.

It doesn't strictly interfere with the operation of the alarm, only the immobilzer circuitry.

You should find it though because a thief could 'jimmy' the ignition lock and energize it's inductor coil which would turn off the immobilizer because of the proximity of the chip.

If you cannot find it, it can be removed from the DME's memory using a PST2 or PIWIS tester, making this particular chip now useless.

The DME can be programmed for up to 4 transponder coils allowing you to have 4 spare keys. Your new key can be programmed into the DME using it's unique 24 digit Code No. (on barcode label on key grip).

Ok, so it has to be in the car somewhere or the car wouldn't start. That was my understanding, from the above statement. I thought it was somewhere in the car but, I just haven't located it yet. So passing a magnet over it won't "scramble" the chip to make it useless? That was my fear and the reason I haven't done that yet.

Thanks for the input, that's why this board is the best. Fast and accurate advice. :)

I appreciate my '73 911 even more when I read these types of posts. Damn electronics sure make things difficult at times.

I highly doubt the transponder pill fell out of the key or the car wouldn't start, even if it is still in the car. The pill must be right next to the ignition for the signal to be received by the transponder behind the dash. You are probably confusing the circuit board for the remote buttons with the transponder pill. They are two separate parts. Look down by the key blade in the inside of the key housing and you will see a small black pill. That is the transponder 'chip'.

-Todd

After re-reading the original post, I have to agree w/ 't'oak on this. If the transponder was lost, the keyless entry/remote alarm should still function. If it's the circuitry board that's missing, these would not function which is what the lister describes.

I'd find it because if it's battery is still attached and it falls on a wet surface, it could short out.

Can somebody tell me how this "energizing" is done ... i.e. is 12v + on ACC supplied to the immobilizer transponder coil wire or is it a negative trigger? Am I correct this is the wires that attach to the immobilizer coil on the ignition? Thanks