MarkMak

I have 2 keys. I have been using only one for the last 10 yrs, may have replaced the battery once before, everything was fine till today. Today the battery was low and the door was not opening. So, I took the working spare key and put its battery into the old key and ordered new batteries online.
Now here is my problem.
1. Old key has new batteries, door lock/unlock works, ignition does not work
2. Spare key has old batteries, door lock/unlock does not work (old batteries), ignition works.

Here for ignition to work you don't need working batteries in the key. But, with good batteries my old key ignition does not work. Could someone help me diagnose the problem with my old key.

Someone suggested to press the lock/unlock key for 10 secs near the ignition switch. This did bring the red light on for a second, but it still did not turn the ignition on.

Note: I did a lot of search in mbworld as well as outside. Found some information on battery replacement and steps to reset the key but none worked for my problem. If there is a post already on this one, please point me to it.

Thanks

Maj. Dundee

Mark, the only function of the disc battery in the key is only for remote unlocking & and locking and has nothing to do with starting the engine.

Your old key is kaput. To satisfy your dilemma, remove the battery in the spare key and you will see that it starts the eng.

DATL

My key would lock/unlock the doors, but would not start my car. I thought it was my starter or something, but it ended up being my key. There was a little wire coil deep inside it that had become partially detached. I could not fix it so am ordering a new key.