On my 03 SL500, the door and trunk locks are not activated to lock or unlock by the remote or the buttons on the dash. I have to use the littlemechanical key to either lock or unlock. When the remote is pressed to lock or unlock the lights flash but the locks are unaffected, so I know it's not the remote batteries. Any suggestions would be appreciated. Fuse?

 

In the manual, it tells you what to try if yo uhave this problem. I just read the whole thing for the first time yesterday and I can't recall it offhand but your owner manual should help with troubleshooting.

 

We had this problem yesterday and the solution ended up being a fuse in the rear sam. The alarm siren and the door unlock mechanism are connected so when the alarm goes bad it blows the fuse causing the doors not to lock.

Try setting off your alarm, if it does not engage this could be the problem.

 

Being a mechanic as my life I tend to hunt problems down with a vengence, alas the lock/alarm system on my SLK. Why they put something so sensative to water in the trunk is beyond me. I know...space, this could have been installed under the hood in a nice sealed container. Mine was going nuts, wouldn't unlock, the alarm going off, ect. I removed the unit from it's protective, what a joke, cover. All the electrical conections were green with corrosion. I disasembled the unit and found condensation everywhere inside. I sprayed all the connections with CRC and CAREFULLY cleaned all the pins and their housings. I put everything in a warm oven for a bit to dry all the moisture. I then sprayed the control board with a non conductive silicone spray. I sealed all the connections with electricians grease and wrapped the unit in a plastic bag then installed it in the PROPER container...hahaha. It works fine now and I will keep you posted to the long term results of this venture. Living on the New England coast is a test of anything electrical