And I never had a key not work for being out of tolerance, although I rarely if ever measured the NEW keys.
I had an old car where this system died and then had the whole key assembly replaced. Months later the system went bad again, and, not realizing how simple the system was, returned to the mechanic. He found the resistor pellet went bad, either because it went out of tolerance or opened. Unfortunately I don't know what happened, but know the second time it was just the key.
Now I have an old car and decided to by pass the resistor pellet because I sense it will eventually fail. To match the value, and having a limited amount of resistor values, I used two in parallel with one in in series. It's about a 20 milli-ohm difference using 1% resistors.
I was a bit concerned working around the yellow air bag wire because I don't know what it takes to trigger it, but have read banging the wire isn't good. I had the battery disconnected, but remained cautious regardless.
Wish I didn't get intimidated by the "high tech" security system because I blew a chunk of time/money having the mechanic fix it for me. I don't remember the cost, but paid for a tow (this was before AAA), paid for the repair, and then months later got stuck in downtown Boston late night. Since the repair was still under warranty, got the car towed to his shop (which he paid for), but wasted a whole night trying to get home. For the cost of a few resistors, I could have saved time/money.