Ignition Key Problems - Mercedes-Benz Forum

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post #1 of 4 (permalink) Old 10-20-2010, 11:41 AM Thread Starter
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Ignition Key Problems

For starters, my apologies if there's an answer I couldn't find through a Google search. If someone has it, please post the link (or the keyword). That would be enough, thank you.

Otherwise, here's the problem: every morning when I try to start my 2004 500 CL, it takes me a dozen tries before the car recognizes the key.

Cleaned key and switch, nothing. Bought a new key from dealer, nothing: same problem. Changed batteries on old AND new keys. Nothing. Main battery is fuly charged.

The weirdest part is, when the vehicle has started once, it goes on and off all day without a hitch. Early next morning, the problem resurfaces.

If I lived, say, in Canada I'd think the temperature change might make a difference but in Miami we go from the 90's to as low as 72 at night.

So, should I go to a stealer & have it install a new switch or someone has a bright idea like check some connection that may loosen up at night?
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post #2 of 4 (permalink) Old 10-20-2010, 01:14 PM
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Could you be a bit more explicit about what happens here?

When you first put the key into the Electronic Ignition Switch EIS (N73) in position 0, do you hear any noise? You should get a 'hand-shake' communication between the IR transmitter in the EIS and the IR receiver in the key, which initiates 'Drive Authorisation'. The noise is the steering lock withdrawing. If everything sounds dead, you have an EIS problem.

The EIS is also involved with the gear selector lever in P, and the stop lamp switch under the footbrake. That's why you have to have your foot on the brake and also be in Park, to enable the key to turn for starting.
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post #3 of 4 (permalink) Old 10-24-2010, 09:03 AM Thread Starter
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Thanks for the reply.

No, no noise. Nothing. Of course, I do have the gear in Park and the foot on the brake pedal. It's as if it didn't recognize the key.

Everything else works just fine. The car opens, switches headlights on, etc. but when I put the key in after sitting idle at night, it takes me anywhere from 3 to 12 tries before it recognizes the key.

What drives me nuts is that, once started and driven a few miles, it keeps recognizing the key at first insertion all day long.
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post #4 of 4 (permalink) Old 10-24-2010, 09:17 AM
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probably have a bad EIS (ignition switch).
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