The GM system was called Pass Key and the chip was a resistor, not a diode. First time the car was started (at the factory), the computer "learned" the resistance. If any other resistance was measured during a start, the computer would shut off power to the starter relay.
The problem was that the contacts inside the ignition switch would wear down over time and not always make contact. This would cause a "different" resistance which the computer would interpret as an attempted theft. A 3 minute timer was also programed in such that every time it sensed the differt resistance, even if you jiggled the key, you were still locked out (and just reset the timer).
I had a '94 Buick that became hit or miss. Thanks to various GM forums, I learned all of this. Then I measured the resistance of my key, got a resistor of the same impedance, cut the wires under the dash and soldered it in. Problem solved.
Is the Jeep system the same? I have no idea - I didn't even know Jeep had an anti-theft system!