Mine, so far is not giving any more trouble but some owners on BW and other forums have been talking about this. Parkrog, a member at BW is really sore about his and is attempting a class action lawsuit against MB over the AAM's. I noted on my VMI that ours had been 'worked on' by the dealer when the first owner had it (I'm not sure it had been replaced, though likely it was). They quit recognizing keys and the dealer sells a new key to program in and it loses it's programming as well. After 8 keys, kiss the AAM goodbye and a new one is over $3,000. As I noted in the above thread, some guys are being told AFTER their warranty is out that the AAM is bad and requires replacement-on their dime! I've alreay lost one key and so far, the two I have are still okay, 1 year later. I know for a fact that 5 keys have been exhausted on mine (I have two, lost one to programming,1st owner lost one and had another replaced because of programming.). I'm keeping my fingers crossed because I have no more than three keys left and that would be bad to lose them.

I noted you had links in your web site about AAM's but I couldn't find any references to keys losing programming in the AAM.

Just to add some information here,  in MY2002, for all W163’s except the ML55, the ECM was added to the Drive Authorization System.  What this means is that not only does the DAS module (which is either internal to the AAM for MY1998/1999 or a separate plug-in component for MY2000+) have to validate the key’s code, the ECM does too.  The loophole that was allowing some MBZ’s to be stolen was that DAS was sending a simple “OK to start” command across the CAN bus to the ECM.  This signal could actually be duplicated by either replacing the AAM or DAS module or simply by hacking the CAN signals.  Now that the ECM also has to validate the key, a thief would have to replace both the DAS and ECM modules; hacking CAN signals or just replacing the AAM/DAS would not work.

Wolfgang - 10/20/2006 4:46 PM

rudeney - 10/20/2006 10:10 AM Just to add some information here...

To add some more info here. Regarding the protocol the ML uses to authenticate a key. Up to and including model year 2000 it uses DAS2b encryption. And starting with model year 2001 in those models using ME2.8, that means not the ML55, the protocol was changed to DAS3. A resourceful thief can break either one, as Noodles and bigcatny pointed out.

You may be correct that the encryption protocol was changed to the DAS3 version in 2001, but DAS3 implementation was not completed until My2002 when the valet key was dropped.  The whole reason for the valet key under DAS2x was that it was used to program a virgin AAM at the factory.  For full “compliance” with DAS3, the ECM also has to validate the key’s code - not just accept the AAM’s validation with an “OK to start” signal.  Because of this, the AAM could no longer be programmed on the assembly line because there had to be a matching AAM *and* ECM installed in the vehicle, and field programming became too complex.  The pre-programmed AAM and ECM thus became part of the vehicle’s key set.  That’s when the valet key was discontinued.

As for a determined thief cracking the code, yes, that could happen, but it’s not going to happen in a dark parking lot in a seedy part of town.  It’s not like you could just plug in some sort of simple device and read the key codes or even duplicate them.  Well, I guess it’s feasible that such a device could be created, but the cost would be something out of the reach of the typical car thief.  My guess is that if you really wanted to steal a DAS3-equipped MBZ, it would be easier to steal the vehicle registration papers from the owner, then use them to claim yourself as a new owner and order a new key.

Keep in mind that the battery in the fob has absolutely nothing to do with the ignition system.  Think of the ML key as if you had a separate ignition key and remote control door lock fob that were glued together.  The battery only powers the remote control locking (RCL) portion.  The drive authorization (DAS) chip within the ignition key is actually powered by the RFID antenna in the truck’s ignition switch.

If the key will not start the truck, then it has become de-synchronized within DAS and will never again work.  There is one “connection” between DAS and RCL in the ML, and that is that a new or de-synchronized RCL fob can be re-synchronized as long as the key that it’s attached to can be recognized by DAS.  If that is the case, you can use the re-sync instructions.  So, if your key failed to start the truck, then it became de-synchronized within DAS.  If you then thought you’d change the battery in the fob, you cleared its RCL rolling code and thus it would need to be re-synchronized, but since DAS won’t accept the key, the whole thing is now toast.

Welcome back! Long time, no see!

The key will start the truck but it will not lock-unlock doors. According to the owner's manual, the key has to be resynced with the truck according to the outlined procedure. I performed the procedure 8 times and never got it to work but I've done it twice before, so I know it's supposed to work. What I've found out is that these keys, apparently, can only be resynced about 2 times, then they will no longer work locking or unlocking. I should have replaced the battery when I was having symptoms that it was going dead and then I would not have needed the resync procedure. Several on BW have stated in a thread that they lost their keys the same way and had to order another one. Even the dealer couldn't get them to lock, unlock.  

cmitch - 3/11/2008 9:30 AM
Welcome back! Long time, no see!
The key will start the truck but it will not lock-unlock doors. According to the owner's manual, the key has to be resynced with the truck according to the outlined procedure. I performed the procedure 8 times and never got it to work but I've done it twice before, so I know it's supposed to work. What I've found out is that these keys, apparently, can only be resynced about 2 times, then they will no longer work locking or unlocking. I should have replaced the battery when I was having symptoms that it was going dead and then I would not have needed the resync procedure. Several on BW have stated in a thread that they lost their keys the same way and had to order another one. Even the dealer couldn't get them to lock, unlock. :confuzed:  

Thanks for the welcome back!  I still lurk around periodically just to make sure you boys stay inline! J
I am sure you are following the correct instructions, but just to make sure, this is how you re-sync a key:
Insert the key into the ignition and turn it to position 2.  Turn it back to position 0 and remove the key.  Within 60 seconds: press and hold the “LOCK” button, and while holding it down, press and release the “UNLOCK” button 5 times (about ½ a second per press).  Release the “LOCK” button, then press any of the fob’s buttons to complete the process.  This is for Oct. 1997 and later builds.  For earlier builds, it’s the same except for the key press sequence – press and hold “LOCK” and then press and hold “TRUNK” and hold both for 15 seconds, then release them and press any fob button twice to complete the process.  This should be done with all vehicle doors closed.
AFAIK, there is no “limit” as to how many times an RCL fob can be re-synced.  Basically what happens is that each time you press an RCL button, it sends a pseudo-random “rolling” code.  It is only pseudo-random because the next possible code can be calculated using a mathematical algorithm.  In fact it can calculate what the next possible 256 codes will be.  Upon receiving a valid code, the will now consider any of the next 256 possible codes as valid.  If your fob’s battery dies or if you  press a button more than 256 times when away from the truck, you will now start transmitting rolling codes outside of the AAM’s known valid set and thus the fob has become unsynchronized.  The re-sync process simple tells the AAM to accept the next incoming rolling code even though it isn’t one of those 256 that it would normally recognize.  Once it does that, it now has a new set of 256 possible valid codes it will accept. 
Keep in mind that this is a bit different from the rolling code system used by DAS.  It does not use a predictable pseudo-random rolling code.  Instead, the AAM chooses another rolling code at random and physically rewrites that to the RFID chip in the key.  If these ever get out of sync, there is no provision to correct it.  Even if you knew the rolling code that they key’s RFID chip now contains, there is no way to program the AAM to accept it.  Although you might find some mechanism for manually rewriting a new rolling code to the key’s RFID chip, there is really no way to know what the code is that he AAM expects.
So, if all this fails, my guess is that it’s a bad fob and not an AAM issue.