Originally Posted by
Herman Minister
You say "The batteries only support the lock / unlock function" but I understood the fob is also synced to the anti-theft system, which would imply that there's a chip in the fob that has to communicate with a similar one in the car. I'm probably wrong in this assumption,
You are right AND wrong at the same time. This is how it works:
1) There are two batteries that power a little radio transmitter, the transmitter sends a signal any time the LOCK, UNLOCK or PANIC buttons are pressed. The SKREEM receives this signal and responds by sending commands to the BCM and CLP/SSM to lock or unlock the doors or to set off the Siren. The FOB can be programmed to the car's SKREEM using the technique you are using.
2) There is an RFID chip in the fob that is powered by induction from the black ring around the ignition switch. When you turn the key to ON, the ring energizes and the RFID chip sends a signal to that ring, this signal is passed over a pair of wires to the SKREEM. The SKREEM tells the ECU "I heard from a legitimate RFID chip, you may start the engine". If this message is not sent to the ECU, you get the "three cranks and nothing" symptom. This is not a programmable function, as the RFID chip is programmed once and only once, you can't alter its programming.
If the RFID chip in the key is lost, you must go to the expense of having a new key made, this is about a $400 task and no dealer I know of can do it. Needswings.com and The Mercedes Swap Shop can make keys.
You say the car will not start, we can't help with that as you are not telling us anything. So, what are we dealing with, is it:
1) You turn the key to START, the starter engages but engine will not start.
or
2) You turn the key to START, the starter will not engage.
If 2), then do this:
Get in car, put key in, turn to START. If starter does not engage, relax key to ON and wait 45 seconds. Is the engine cooling fan running LOUD and FAST? If so, replace the RCM.
If the fan does not run fast, yank the battery cable off for 15 seconds. REconnect, try again, if now the starter engages, engine starts and dies, try again, if you get 2 or 3 of these false starts, then no starter engagement at all, you have a SKREEM/RFID issue - call Needswings or The Mercedes Swap Shop.
If it is 1):
Yank battery cable as per 2) above and reconnect. If you get two or three "false starts" then nothing, call Needwings or The Mercedes Swap Shop.