I have a serious issue with my '07 Crossfire Roadster, and I really hope someone here can help me with it. I replaced the batteries in the key fob and now the key won't re-sync to the car. I've tried what I believe to be the re-syncing process (insert key but don't turn it, press lock button twice, turn key to 'run' within 30 seconds) but to no avail. All the lights on the dash come on, but the car stubbornly refuses to start. I'm at my wit's end over this: obviously I can't start the car at all right now, and unfortunately I lost the second key fob about 15 years ago, so this is my only one.

I read somewhere that a dealership might be able to re-code the key fob, but the few I've tried have told me that I'd have to take both the fob and the car to them. So no help there. On top of all this, I've also read that a replacement, correctly-coded key fob from the manufacturer might cost around $650. I can buy an iPad Air for less than that!

So any advice would be gratefully received. As you can imagine, my beautiful car's worth nothing to me at the moment - just a big, immovable block of metal in my garage. I'd really like my Crossfire back.

 

What makes you think it is the key? Have you tried replacing the RCM? Was it starting before you changed the batteries? The batteries only support the lock / unlock function, not the starting function.

 

Thanks for the reply. I think it's the key because that's the only variable - all I've changed is the key fob batteries. The car started before I changed them, won't start after I changed them. It seems far less likely to me that a random component would fail when the car's parked in the garage, at the exact moment I change the batteries in the fob.

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, but it seems logical to me. Therefore, the fob batteries would also be necessary for that chip, would they not? Obviously, all my assumptions may be wrong, and I'll be the first to admit that, but I'm just trying to wade through this quagmire as best I can.

 

I second that. The chip in the FOB is not connected to the circuit board. It is just glued to the inside of the case.

 

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.

 

I would also check the starter battery, how old is it? It is surprising how often two things fail at once.

 

Look at your key fob in a dark room. When you push the button do you see a red light?
If not, then the top battery connector is not making contact with the battery.

 

Thank you for this information - it's very useful to me. Thank you also everyone for being so patient and supportive.

The symptom was number (2). I would insert the key, and turn to the first position. All the dash lights would come on, and I could hear the pump running in the back. I would turn the key to the second position, and nothing. No solenoid clicking, not even a ghost of starting.

However, after trying to start the car many times it eventually started. Because of this I've concluded that it must be an intermittent fault, because on each attempt at starting I did nothing any differently. I've read elsewhere on this excellent forum that the RCM can develop dry solder joints, which would explain the intermittent nature of the fault. I need to know that the car will start every time, so I've decided to buy a replacement RCM and have it fitted to the car.

I apologize for my late reply, by the way. I have no good excuse.

 

I concur with the RCM. It is plug and play and takes 10 minutes to swap. Instructions are on the internet. Send the old on to DJ TIGHE , have it rebuilt for much less than the cost of a new one and carry it as a spare for next time.