mmuthart

I've been reading and reading, and was shocked to see all the related threads. Unfortunately, there appears to be many different causes and not many people reporting back with final solutions.

Here's my situation:

New to me (3 months) '05 CDI with 85k miles. I felt fortunate that everything worked on my car....well that changed a couple days ago. Car wasn't driven for a couple days and battery voltage dropped to 4v all of a sudden. Car had sat before for days without issue.

Main battery is a year old and is genuine MB. Small battery under hood is 2 years old (also MB) and I measured over 12 volts on it, so I don't think it is part of the problem.

With the car running, I measured over 14 volts at the big battery, so it appears to be charging great.

I trickled charged the battery back up to 12+ volts. I removed the negative battery cable and put a test light between the cable and negative post on the battery. (The car had been sitting all night; I didn't open any doors, so it should have been as fast asleep as it would ever get.) The test light burned brightly!

I removed every fuse I could find one by one, but the light never went out.

I had read some threads on the alternator diodes and voltage regulators, but I'm not sure if the alternator could be an issue even though it charges just fine.

Can the alternator cause a parasitic drain, if it charges just fine?

One other tid bit, with the test light still in place, I removed the larger red cable to the positive post on the big battery. I assumed this was the charging cable from the alternator. With this cable removed, the test light flashed. I don't know what that may point to...

Any ideas? Next steps? Thanks for any help with this!

vettdvr

Did you do your test with the trunk open. The light to the trunk pulls power and the computers stay on. You will have to run leads out of the trunk, close it then wait until the computer times out then check the current draw.

mmuthart

Yes, the trunk was open, but the interior lights in the trunk had gone out.

Even with the trunk lights out, do you think the computer was not fully 'asleep?'

Because I spilled a little bit of DieselKleen in the trunk a month or so ago, the car has been sitting with trunk open (to vent) overnight for weeks. There was never an issue starting the next morning; so I assuming, with the trunk open, the car will still go fully asleep.

Right now, I'm leaning towards a shorted diode in the alternator. I've read that this can cause a drain. At idle, I did measure 14+volts at the big battery, so assumed the alternator was good. I'm thinking that maybe this test is not conclusive. I'll call around and see if someone can do a more complete test of the alternator while its in the vehicle.

jandmtv

The lights might go out after a while, but the car still knows that your trunk is open and will not let the computer sleep.

Recharge your battery. Close the truck and lock your doors every night. See if the problem comes back.

mmuthart

I will do exactly this when I get home this evening. But I'll leave my test light hanging outside as previously suggested. If the draw on the battery stops I should know within a half hour when the computer should go completely asleep.

Thanks for the suggestions so far! I'll be happy if this turns out to be a non-issue that I brought on myself by leaving the trunk open...we'll see...

mersum1es

Mine sleeps, or at least draw current drops to 50mA when lights go out (about after >5 minutes).

Trickle charger may keep computer alive, I've not measured that.

http://www.mbclub.co.uk/forums/1790471-post6.html

mmuthart

UPDATE...

So last night I closed everything up and locked the car. This morning I was able to unlock with key fob (good sign). I opened the trunk and measured the big battery voltage - 12.33 volts. Drove the car to and from work and had no issues all day. So I was unable to duplicate the drain to 4v overnight.

Tonight I will close everything up but leave it unlocked and check voltage in the morning.

I've abandoned my method of test light between negative battery post and battery cable. I think it's to simplistic for this complicated vehicle.

mmuthart

12.3 volts again this morning without locking the doors. So still unable to reproduce the drain to 4v overnight.

Tonight, I'll leave my Belkin Bluetooth receiver plugged in to the cig lighter, like it was the night it drained.

ptkacik

My 05 CDI also drained to 4volts. I needed another battery but am curious what caused the problem with yours. Did you ever figure it out? Am I due for a bigger problem? Thanks.

Tschuss_Bill

I'm curious about the follow up on this one too. I've had mine drain sporadically a few times. Never did figure it out. Seems fine now, until next time.

There are a couple CDI issues that I've had and read about that I've never solved, nor have a I seen a post that's led to the answer. The draining battery is one, the other is the hot hot air on startup from the heating/cooling vents.

-Bill

boardboy330

I think I might have an answer - but I am NOT sure.

I noticed a few months ago that the car tried calling SOS for some reason. I could start the car and it would continue over and over. I didn't understand why because it was random, or so I thought.

Anyway, I broke a wheel driving to NY and had to have the car towed. I asked the GM to code out SOS because of the issue. He said, most likely the rear handle to the trunk is getting stuck and causing the computer to think the car is being stolen. He said it was a common issue and they've fixed many.

Since I stopped using the trunk latch, and only use the inside button or keyfob - the issue has stopped. The car has not been dead. I will say, it took a few days of sitting for it to die, but it might be something to look in to.

Also, someone posted a diagram a while ago of common battery drain issues here on the forum. You may want to check that out.

mmuthart

Unfortunately, I was never able to reproduce the issue nor has it returned. I do keep my trunk closed overnight now just incase it was part of the issue, but I have no confirmation that that was the case. I also keep my BlueTooth puck plugged into the cig lighter at all times.

So far so good on my '05 that I will have had a year come November. During the colder months I was getting a scary red warning about the brakes. I believe I tracked that down to the steering angle sensor in the steering column. I have not seen the warning since the temps warmed up.

Good luck tracking down your issue. These vehicles are definitely intimidating when it comes to all the complicated electronics.