Keyless Go- one key works, one doesn't
 

Recently purchased a new-to-me 2008 550SL. Absolutely love it- low miles, and a fantastic ride all around. When we purchased the vehicle, I noted to the dealer that one of the keys batteries needed replacement. They claim that they did indeed replace the batteries, yet the keyless go is not functioning with one set. Works fine with the other set. The push-button works fine to lock, unlock and open the trunk, but will not open the doors by pulling on the handles, or lock them by pushing the button on the handle. When engaging the start/stop button, the car indicates "key not detected". Any ideas here? The car will start fine when the key is inserted.

Your feedback is appreciated.

JVN
Tampa, FL

Since the key works to lock and unlock the car via its fob buttons, then the batteries are installed properly and working. In that case, there are a few possibilities. One is that the key is defective and its KeylessGo functionality is not working, but its other functions are. If so, there's not much you can do about it. Another possibility is that this is a spare key that was ordered by the previous owner, and the parts desk ordered the wrong one (i.e. one without KeylessGo). If that is the case, then there's nothing you can do about that.

Finally, it is possible that it is the proper key and is working correctly, but it was never programmed into KeylessGo. You can try this: get in the car with the key and press and hold the Start/Stop button for a few seconds until the "Service Required" message appears on the instrument cluster. If the key works and is recognized, the ignition with switch on the accessories. Move the gearshift from park to reverse and back to park. The ignition will shut off and the key should now be programmed.

There are also test and programming that can be performed via SDS (Star Diagnosis, the master computer diagnostic system for the car that dealers use).

Thanks Rudeney. I'll give your tip a try. Need to run by the dealer soon to pick up service records that were not included with the car- as it was serviced locally for a few years. Appreciate the feedback.

JVN

Also possible that the batteries in non-working key are partially spent. I had same problem with my key--unlocked doors, etc., but wouldn't work keyless go. No warnings on dash. New batteries solved it. Bill

WOW!

I'm working through a similar issue. Here it is in bullet points:

1. In 2009, bought a 2007 SL550 with 12k miles on it. Only one key. It has keyless go.
2. Negotiated that the used car dealer to have them take it to MB dealership and have another key programmed for the car before I took delivery. They did. When I picked it up, it had 2 working chrome Keyless-Go keys.
3. In like 2013, I was deep cleaning the car and found where the 2nd original chrome key had been. It had slipped deep down in the crevice between the bottom and back cushions on the drivers seat. Looked like a brand new key!
4. I brought it in the house and tossed it in a drawer as I had 2 perfectly fine working keyless go keys already.
5. A few months back, one of the two stopped working completely. Swapped batteries but no joy. So I was down to 1 key.
6. I pulled the "lost key" out, replaced the batteries and I get exactly the same results - fob buttons work. Starts car when inserted into EIS control unit (key hole). No keyless go function.
7. I've tried the methods described here as well as the "spare key" procedure listed on the attached MB service doc.

They told me when I bought the car and they took it to MB to program the extra new key that they wipe the previous keys from memory. Clearly that didn't happen. But something is happening that prevents Keyless-Go from using the radio signals but not the EIS control unit from using the coil to start car. Seems like it has to be the same "serial no." or code for both the wireless and "wired" ignition commands.

Still working it through...

The codes read via the IR interface of the EIS and those read by the RF signals of KeylessGo are totally different. A newly ordered extra key should work out of the box to lock/unlock via the fob buttons and operate the EIS, but it won't work for KeylessGo until the car is programmed to accept that key. When the dealer programmed KeyLessGo for the new key, it actually wiped out the programming for all KeylessGo keys and then only enabled the two they had..

An interesting observation about this lost and found key - its battery must have been totally dead, because if it was detected in the car, it would have been programmed along with that extra key.

I tried pressing and holding the start/stop button, but I never get the "Service Required" message on the instrument cluster. What would cause that?

Looking back at WIS, those instructions are only for cars through MY2008. I've tried it with mine (MY2011) and get nothing. Or, maybe it only works if you have a non-programmed key in the car?

You're right. I just checked the document as well it says MY08. Hmm wonder if there is a different procedure then. I had the key that the keyless go doesn't work with me (all buttons and turn stating work).