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How does a car key turn on a car? Answered

I was wondering how the inside of a car "tumbler/ ignition" worked? How does it know that it is the right key? and Is there a switch to tell if the key has been turned? or is it some digital encoder?



8 years ago

Oh, I was just going to add that on older vehicles (mid 80's?) the actual switch that used to give the starter motor power was actuated by a rod from the ignition tumbler turning. The switch was usually located down on the steering column somewhere, sometimes at the base. I imagine the newer cars don't use this mechanical actuation anymore, lots of them have the ignition switches on the dashes now... Just like they did waaaaay back in the old days.

In most modern cars, the mechanical lock and switch is only part of the mechanism. The second part is electronics, through the VATS or transponder system. VATS uses additional electronics in the car to check that the key was cut on the right blank, out of a set of ten or so for each keyway, via a set of electrical contacts. Transponder systems check for the specific key via a short-range radio linkage. Typically these use a cryptographic challenge-and-response system, so simply recording the response and retransmitting it won't work. The transponder recognition typically takes place deep in the car's main computer, so you can't extract the information from the car either. Most new cars use transponder systems. That makes the keys more expensive -- and makes obtaining additional keys a lot more complicated -- but does deliver significantly higher security.

This type of ignition (like sean says) is essentially a switch connected to a lock. A bit like a door-lock with a switch directly connected to it instead of the door bolt.
Because locks can be forced / picked it's not uncommon for cars to have separate immobilisers as well.


the first part is lock..look up "lock" on wikipedia for a thorough, authoritative answer with all the bells and whistels included. the lock is connected to a switch matrix, this provides power for the auxiliary systems and ignition system. turning it farther (sprin loaded) engages the starter motor, which then turns the engine. Since the ignition system is "ready to roll", the engine fires and starts turning on its own. Releasing the ignition switch disengages the starer motor once it has done its job