After replacing the battery I'm still having troubles.
History:
In May the car randomly shut off on me after coming down the rough mountain (~1 hour drive.) This happened while moving but fortunately I had a place to pull off. I waited a minute and it started back up.
Fine for weeks. Then it happened again while moving, pulled off into a Barnes and Noble. Waited, started back up and drove fine for hours the rest of the day. Fine for weeks.
Then about 3 weeks ago, sitting at Sonic for about ~30 minutes I had a dead battery. Friend came and jumped me off. Put it on the trickle charge. Ran fine for a week. Was an hour away from home, car wouldn't start. Lights were dimming, Mercedes kindly jumped me off.
Replaced the battery from NAPA. $175. Next day, wouldn't start. Touched the battery charger to it and started. Ran fine for days.
Again, shut off on me going down the road.
Took it to Advance to check the battery/alternator etc. The printout gave the following results:
Battery Test:
Good Battery
Voltage: 12.81V
Measured 1046CCA
Rated 685CCA
Temperature 90F
Starter Test:
Cranking Normal
Voltage: 11.54V
Amps: 236.3A
Time 953mS
Charging System Test:
No Problems
No Load:
13.87V
13.1A
Loaded:
13.41V
4.3A
Drain Test:
12.03A
Suspect
Now I know with the drain test the car might not be totally asleep yet, but isn't 12.03A a little high?
So I'm trying to find out what's draining the battery. Using my little voltmeter, the grounds all seem to be good. But I'm wondering what could cause it to drain so bad that it would cut off while going down the road.
While playing with the voltmeter I did find that it had a pull on it after ~15 minutes. I don't remember how much but it was enough to make me go "whaaat?"
My "car expert" friends are kind of stumped. One says starter because it completes a circuit and if it's messed up it could cause all those problems (not smart enough to know quite what he's talking about.) Another says it can't be starter because it does it while going down the road and it must be alternator.
Any advice is greatly appreciated. I don't want to the dealer$hip without a definite problem.
If it's any consolation, when I 1st got my R171 back in Nov 2004, the battery would go flat after about 2 weeks of none use - I took it to my local dealer, and they could not sort it - finally I sussed it - I used to leave a phone in the cradle permanently, and that would flatten the battery in about 10 days - I leave the phone out now, and it will start no probs even after a couple of months standing.
Thanks for the quick response. Nothing of the sort inside or new parts. The only thing I could possibly consider "new" would be that I changed my headlamps about 6 months ago. They're really bright
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Hmmm, I can tell you 12 amps is *way* over the top for "at rest". I'm like you, I'd wire in the amp meter, and start pulling fuses till I saw a big drop in consumption and then focus there.
CAN bus becomes active almost immediately when you unlock the doors, and cranks up the MOST ring and all sorts of other stuff, so close the car, open the hood, wire in your meter and let it go to sleep - 10-15 minutes tops. I want to say you should see like a half amp in this state, but I'll see if I can dig anything official up.
The problem when I try to do it is that it only does it randomly. The last time I saw personally saw it drop the battery charged right back up within the next two minutes. Any ideas on how to force it to happen? I can't drive my car anywhere with it shutting off like this.
Your lucky in that owning a 170 the MOST and a lot of the CAN stuff John mentions does not apply to you, the car is fairly simple electrically.
12 amps is a shed load of power, John is spot on with the fuses, what you want to do is measure the drain current then you can narrow it down, for example a 10A drain will rule out the fuses below it and so on.
Went out to check the fuse box today. Car started instantly, couldn't make it drain for 3 hours. Looked at the fuse box under the hood and drivers door bay. Couldn't get a drain to start and didn't see a difference by removing fuses.
Interesting note I forgot to add.. When the car doesn't start the electrical fan starts like it's too hot even if the car has been sitting overnight.
Ideas? Should I take it to dealership? What can they do differently?
Days gone by, still starting and running fine. It's just a matter of time before it acts up and I need to move the car back up the mountain for school. This is frustrating
I've been having the same problem just don't have the time to chase it down. I can jump the car and drive it for hours, the next day the battery is dead and its only two years old from the dealer. If you happen to find the drain post it so i can have a look at mine. Thanks
It's warmer now and it's having trouble again. The fan also acts like the car is overheating when it hasn't even been started.
I did the fuse pulling, nothing found.
Ideas?
A lot of power is being consumed without blowing a fuse, so something is consuming. I hope your car is overnighting in a garage. From now on leave the windows down after you park the car and 30minuts to an hour go back to it, listen and look for anything on or running.
I have same kind of problem in my other car. We found out it's the ground wire of the battery screw up with the rusted. Try check the ground wire cable and tighten it a little bit. I did this and solve my problems. Hope it can help. Good luck !!
Okay, so the problems previously mentioned went away for a long time. No more loud fan or random shut offs. The K40 did fix it.
New problem:
Battery died a couple weeks ago. The car did sit for nearly a week in cold weather, I figured that might done it. But it was still under warranty (from the new one I put in it) I took it to two places and had my charging system checked. No problems.
To get it started that day, I just did a normal jump. The lights varied from bright to dark in cycles.
I did a slow trickle charge on it that night. I considered that I might have left something on, too.
Weeks go by, no symptoms.
Yesterday, left the house. A few feet down the road and the ABS light and another blinked for a split second, the car jittered for that split second. Then no symptoms. Everything was cool. I went to the mall. Parked. Got out. Tried to lock the car with my remote. No response.
Got inside, the battery was completely dead. No clock. No nothing.
How did the battery just die?
Connect jumper cables, and an easy start...
I checked for loose cables - it doesn't appear to be the case. I could be wrong but I tightened them up the first time it died thinking that was it. No rust either.
no ideas come to me on a 170. Does it have seat control units? common on a 203. your rest current should be less then 50 milliamps. or .050 amp. You need to hook up a meter in series to measure amperage. You also have to have all the doors/latches closed and access to the fuse boxes. Then let the car go to sleep. When can is awake you are going to see 10-20amps. let the car sit 15minutes and it should drop drastically. hopefully it does, next step is one by one pull the fuses, and wait a few minutes between each one as pulling it can wake up the can system and will need to sleep again. good luck.
Battery Drain 
2004 Mercedes Benz SLK 350 6sp MT
2002 Mercedes Benz SLK 230
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