Date registered: Dec 2004
Vehicle: CURRENT: 2007 CLK550 Cabriolet, 2002 C240 FORMER: 2001 ML320, 1984 300TD
Location: Birmingham, AL
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Here's how this works. MBZ has a specialized corporate department that manages keys. When a new vehicle is built, this department's computer "randomly" assigns 24 unique key serial numbers to than VIN. No person ever sees these serial numbers; they are all stored in a secure database and indexed by VIN. The 24 assigned key serial numbers are electronically programmed into a virgin DAS and ECU that are then delivered to the factory, along with two keys (key #1, segment #1, and key #2, segment #1) to be installed into that specific vehicle.
Remember that the 24 serial numbers are matrixed into 8 "key numbers", with 3 "segments" each. While all 8 key numbers can be active at once, only one segment per key number can be used. When a key is lost, it can be disabled by a key with the same key number but the next higher segment number. If all three segments of a particular key number have been lost, the dealer's SDS can be used to disable the entire key number, which will then reduce the 8 possible simultaneous keys to 7.
Once programmed, the DAS and ECU modules cannot be re-programmed through any official means, i.e. not with any equipment the dealers or factory have access to. There are rumors that "someone" has cracked this and has equipment that can reprogram DAS and/or the ECU, but until someone actually shows me hard evidence of that, I will remain skeptical. I know it's physically possible because these codes are just stored on EEPROM's, but there are security features built into these chips, plus the available system interfaces do not include the provision for reprogramming. Reprogramming would likely involve removing chips from circuit boards and using hacked EEPROM programming equipment. This does not sound like an inexpensive nor safe process for expensive MBZ electronics.
Any key that is to work with the vehicle must be programmed to match one those 24 codes programmed into the DAS and ECU. It can't match an existing key's serial number because they keys use rolling codes in addition to the serial numbers. Each time you use the key in the ignition, DAS writes a new random rolling code into the key. If you were able to clone a key, and then if you ever used both keys, the rolling codes would get out of sync and then DAS would disable the entire key number and then neither would work.
The only way to get a new key is to order one from the PDC. They don't ever know the actual serial number programmed, but their computer does based on the VIN in their database. It can program either an additional key number (based on the database records of all keys ever issued for the VIN) or or a replacement key given the key number (1-8) to be replaced.
If you want an additional key, all you have to do is go to the dealership's parts counter with your ID and proof of ownership and order it. It will be delivered ready to use - no dealer programming necessary. That will cost you about $230, and you can sometimes negotiate a lower price. Parts counter employees are usually not on commission and will often discount parts if you ask nicely or build a relationship with them.
If you want to order a replacement key for one that was lost, thus disabling the lost key, you will need to take your vehicle along with ALL available keys to the dealer. A tech will use SDS to determine which key numbers (not serial numbers, just keys 1-8) you have and then check with the PDC to see which key numbers/segments are missing, and then order a new segment for a missing key number. If any key number has had all of its segments issued, the tech can disable that entire key number. This will, of course come at a price, which will be about an hour of labor.
So, if you aren't worried about someone ever finding the lost key and then knowing it goes to your C320 and thus being able to steal your car, then all you need to do is order that $230 new key.