Auto key resistor pellet changed value

Can someone assist me with this very strange problem? My car came with a
security feature where it includes a resistor pellet on the key. Obviously
this is linked to a comparator that determines if I have the right key or
A few months ago my car's security system gave me problems and in the
process of repairing it they needed to change the key cylinder and give me
a new key (and a spare key).
The new key was a different cut (because of the new cylinder) but contained
the same value resistor pellet as my old one. I know the resistor values
were identical because I measured the old one, the new one, and the spare
Last night my car wouldn't start. After having it towed, the repair guy
asked if I could bring my spare key to him. Then the car started!
He took the key I've been using (that didn't start the car) and measured it
to be 6k while my spare key (that started the car) was the 7.5k my car's
security system likes. He did some research and heard the key can become
"de-magnitized". I'm in electronics and know resistors burn and open, they
never change values especially becoming less resistive. Assuming the "de-
magnitizing" theory to be true, I thought about what I did from when the
key worked till it failed. The only thing I did was put the keys in my
pocket along with my cell phone.
If you look at the list of resistor values for keys, the 6k is the value
before my 7.5k. I find this fact to be facinating but yet I have NO idea
how a resistor pellet could become less resistive. I also inspected the
pellet for cracks or chips and didn't see anything.
Is the resistor pellet made from some other material that can become less
resistive? If anyone can answer this, you'd allow me to sleep better.
Thanks in advance!
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find a new mechanic.
you havent been in electronics long enough.
make new key, destroy old key, carry spare key in wallet, sleep well
Reply to
I had similar problems, turned out in my case that the connection to the key contacts wore out and the result drifted.
The system will accept resistance about +/- 10% from nominal, so you may have had a 6K on the high side and it was accepted. The system works in most GM cars by having the resistor control a small and rather hidden module. This module sends a squarewave of specific frequency to the engine computer and also controls an interlock relay on the starter circuit. Hard to troubleshoot because the Mitchel manual does not detail it for 'security' reasons. The companies that sell remote start controls have instructions on bypassing the feature so a remote start will work. Bill Kaszeta Photovoltaic Resources Int'l Tempe Arizona USA
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Bill Kaszeta / Photovoltaic Resources

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