Hi. My 2001 CLK 320 won't start. The battery reads 12.4v and the factory alarm and other electricals work fine. When I attempt to crank the ignition, the engine doesn't even attempt to crank. I checked all the fuses with a multimeter and everything was fine.

I also cleaned (sanded) the battery terminals.

Anyone have an idea? Please help.

Thanks

 

How old is the battery. Anything over 3 years and you are on borrowed time!

I suspect your battery is DEAD. Below 12.4 volts (on load) the battery is irrepairably damaged.
I guess yours is 12.4volts OPEN CIRCUIT NO LOAD!

Whats the voltage with your headlights on??

Get a new battery and have the charging circuit checked to ensure that the alternator is working correctly just in case this was the cause of the original problem.

Was all OK up to this point? Did you leave any lights on etc?

Don't recharge because you will have more problems in the future even if it does manage to start the car on this occasion.

Stuart

 

The battery originally died because I left the car un-driven for about 1 month. I dont remember how old the battery is, but I'm pretty sure it's older than 3 years. It was fine up until this point.

The 12.4v was read with the car and all electricals off while the battery was connected to the car. I'll check tomorrow to see what the voltage reads with the headlights on.

Thanks

 

Modern cars have what is known as quiescent drain on the battery. Even with everything turned off there is still a drain in order to keep the computers partly awake.

As the battery gets older its ability to hold it charge and therefore support the quiescent drain deteriorates. After 1 month things are getting borderline even with a good battery.

I think a new battery will be a good investment.

Stuart.

 

Not sure what onload vs open means... but if the car is off, my battery measures 12.4v. With the headlights on and engine off, the battery reads 11.6.

My gas is on the last 1/4 mark... if that matters.

Also, when I arm the factory alarm, the headlights blink 3 times. Is that normal? When I unarm it, it only blinks once.

 

You need a new battery! PERIOD.

Onload means when the battery is supplying load (i.e. headlamps ON).
With the headlamps on I would expect the voltage to be in excess of 13v. The starter motor requires much more power than the headlamps.

Offload (OPEN CIRCUIT) means everything OFF and voltage measured across the battery terminals. Below 12.5v offload the battery has had it.

Security system feedback is different in different countries. Not sure what the regime is in the USA but it is in the handbook. Doesn't sound unreasonable since I know that in the States you dont use the Direction Indicators as we do in Europe.

 

Are you saying that with the headlights ON, my battery voltage should read higher (+13.0) than when the lights are OFF(12.5)?

Thanks for your help

 

No,

Sorry after re-reading the post it was somewhat confusing.
With the headlamps ON the battery voltage will be even lower than with no load.

In simple terms if the battery is less than 13v with the headlamps ON the battery is "flat" and needs to be recharged or replaced.

If a battery with NO LOAD on it goes below 12.5 it has had it PERIOD. Its a waste of time even trying to recharge it since although it just may recover to restart the car after an extensive recharge it will let you down without warning at some future point.

Stuart