I made the mistake of disconnecting the ML55's battery during repairs trying to be safe. Now I am locked out of the radio.

This is the most idiotic feature ever. I used to be a Pioneer authorized warranty center back in the 90s when they started adding this to head units. Still, we had several come thru the shop needing the code chip because the customer "got it from a friend".
I saw then this was no theft deterrent.

So, can I still obtain the code from the dealer for an '02 ML55 if I show proof of ownership?

That should not be a problem.

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600SEL '91
300E 4Matic '88
240D '83
280SE '77
350SE '73
The most complex systems can fail in the simplest way.
Contra verbosus noli contendere verbis, sermo datur cunctis, animi sapientia paucis.

i don't believe in the lord! He's never bought me a Mercedes Benz.

My wife drove the '99 up to the local stealer, they came right out and punched the code in for her, no questions asked. We're the second owners of this car and we've never bought anything from them; other than an occasional wiper blade or bulbs, so it's not like they know us. Is there no card with the code printed on it in the owner's manual? Or are you a moron like me, and took it out and put it in a 'safe' place? Yeah, the code thing doesn't seem like much of a deterrent. Maybe they're more diligent with newer cars. Fortunately, nobody steals factory radios.

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Remember, Safety Third!
'99 E300 Turbodiesel, '82 300TD, 1996 12V Cummins Turbo, '94 Neoplan - Detroit 6V92TA