Helping a friend with his 07 SL. He parked the car in his garage and did not have it on a tender. When he went to start the car nothing happened. Of course the consumer battery was dead. No voltage at all. The starter battery was also very low. He put it on a slow charge and got it back to 12 v. When he tried to start the car, nothing at all. Now he has replaced the consumer battery and the batteries in the fob and still nothing at all. Nothing with the key in the dash or from the keyless go. Any thoughts where to look to resolve this ?

 

Anything at all? Click from the starter solenoid? Does the ignition come on?

You can start and run the car without the rear battery. Something is wrong in the starting circuit.

First try to jump start the car from the front battery and see what happens.

 

Nothing. Like no electrical connection. Both batteries are correctly connected with 12 volts.

 

With the car off, you need more than 12 volts at both batteries.

The starter motor died without warning on my 2003 500sl at about 125kmiles. Turn key and hear click, no crank.

 

Jump start the car with high amp jumper. See if the car starts. If the front battery is dead, no trickle charger will bring it back to life. This is what happened to me. Tried trickle charger and jumping the car with cables running from another vehicle and nothing.

Bought a high end, high amp jumper and the car started right up. When I disconnected the jumper and turned the car off, dead again.

I say all this to say- you may need a new starter battery.

 

Went out to the garage to open the hood to try some of the suggestions. Interior lights came on this time. Touched the keyless go button and it started right up! What the heck?????

Never had anything like this with my 03. But I don't have the keyless go with my car.

 

Check for rodent damage if you can't get it started. Our first slk350 had this happen.