I have a 2005 roadster with 40,000 miles. Approx 1 month ago I experienced a dead battery. I had the battery replaced ($149.00). A couple days later dead again. I checked the battery and found it to be defective (Charging system checked out fine). I exchanged and got another battery. About 2 days later dead again. The car would not even jump start. I had it towed to a dealer, and they determined that the aftermarket radio (Alpine 9886) was drawing too much power and ran down the battery. They said the charging system and everything else was fine. I promptly had the radio removed, and I have returned it to Alpine (warranty). I drove the car for 10 days, without a radio, and had no problems....... until yesterday. Dead again. I was able to get a jump this time, but noticed during the jump my spoiler popped up?! I was on my way to shop when the car stalled in the middle of a busy road at 4:30 in Tampa. Ouch!!

I have since been told that everything is checking out fine. Could this be a bad engine control module, or something of that nature? No one seems to know what to do.

Thanks for any advice.

 

Gotta go to walmart and buy a voltage meter that plugs into the lighter outlet. See the voltage, start the car see the voltage rise by about 1 volt.

Drive the car and see the operational voltage, look for like 13.7 to 14 something when cold. If the battery is up during driving, I dont think it is, then there is a load that is a phantom. Seat controls are a good load that you cant find, ask me how I know..

TO solve problems you have to know the parameters ( voltage ) to see if and when it gets better or worse. WEEKEND enjoy, Woody.

 

May not be helpful, but early on I had two instances where my trunk did not close completely and the trunk light discharged the battery over a few days. BTW, I like Waldig's suggestion because I like an analog voltimeter gauge in car -- this would be good for diagnostics.

 

This is one of those threads that concerns what I do for a living - I am not a mechanic, but local garages bring cars to us when they have a "battery drain" problem. Police and other public safety vehicles come into our shop ALL THE TIME where the complaint is: "Battery goes dead from time to time". or "Battery goes dead on the weekends". (This last one is most common ... any drain of an amp or two over the weekend will usually take a battery down enough it can't start the car).

I am convinced that the ONLY way to find this is to use logical troubleshooting techniques. A voltmeter WILL tell you if the charging system is working, as you will see the voltage rise with the engine running. But it won't tell you anything more. Voltmeters cannot tell you where current is flowing.

How we do it:

Pull the positive battery cable off and insert between the battery and the cable an ammeter (see link below for the kind of meter I am referring to). You will need clip leads for this - and try to not let them come into contact with any grounded metal. If this sounds too scary, insert the meter in the GROUND CABLE as described. IF the leads touch ground now, you won't blow any fuse or set anything on fire - you will just short your meter out and it won't see the current flowing - but you will not damage the meter or anything else.

The drain you are looking for could be as little as 1/2 amp or less. Use a DVM or some other meter that will display currents down to .02 amp. Current drain of under .1 amp is probably normal. .1 amp is 100 milliamps. We often see drains of 20 to 70 mA (.02 to .07 amp) that are there to keep up memories in the various modules in the car.

But if you see anything over .1 amp, start pulling fuses until you find out where the current is going!

Once you find the fuse that causes the drain to go down to an acceptable value, you have found your problem.

Do not expect most garages to be capable of this - it's a simple test but most mechanics are MECHANICS - it is not up to them to understand what "voltage" and "current" actually mean.

So, get a REAL meter: Fluke 27 II and 28 II Digital Multimeters

And BEWARE - these meters have fuses in them. IF, suddenly, you see no current flowing - verify that the fuse is good before you assume anything! On the low scale, the fuse will blow at something between 1/4 amp (250 milliamp) and 2 amps (2,000 milliamps).

DO NOT WASTE YOUR TIME TRYING TO USE A BIGASS AMMETER you have GOT to be able to see small currents. GET A DVM OR DMM like in the link! Look for a DC current scale of something no larger than .200 amp (200 mA). You will find several fuses that are responsible for 10 or 20 mA of current - no big deal. But I bet ONE fuse will be carrying .1 to 2 amps - that fuse is feeding the culprit of the problem!

Even Lowe's and Home Depot PROBABLY have DMM's with DC current scales of .2 amp!

 

Good job, hope I do not have to use this at all but thanks.

 

I've got the same battery drain problem... 2004 LTD 6-speed. I once came out into a parking lot at night to find the left rear light on... only the left rear!!! If you find out what it is lemme know... (it's not the aftermarket radio)

 

I had a Maverick 'not from Alaska' that would turn on the dome light when it got below about 35 degrees. Never saw it cause the car had to cool to that point.........Weird. Neighbor told me.

In place of a ampmeter, you can also use a small light bulb like on a lawn tractor to see if it lights a bit. If not use a brake bulb to see if there is a drain with everything off. Smaller bulbs will show the clock, computer and radio memory so dont use them or youll get false readings. It is a cheap work around for the tool poor among us. Woody

 

Thanks Woody... I'm selling... can't get parts anyway. Buying a real SLK.

 

I have had problems with the trunk lid - my wife never seems to be able to close it tight and it leaves the light on - I usually find out when I go to lower the top and it doesnt open until I close the trunk properly. The struts on mine are getting harder to open and close and the wife never gives it a tug to make sure it locked.

As far as 1 tail light goes - this has a Euro? park light system and you can leave either side on - there is a P with an arrow for left or right - check your headlight switch and make sure it isn't in the wrong position. (should leave a front light on too but worth a try)