clb0099

Hello,

Recent problem that I can not find the solution to fix. 2008 Mercedes GL450 with 94k miles on it. The car has a brand new battery as well as auxiliary one installed this week and yet the next morning after being parked all night the battery is completely dead. I put the jump pack on it and the voltage reading on the battery is 5.0… I am sure there is some type of draw but don’t know where it could be coming from cause nothing has changed. Any help would be great. The starter & alternator are original.

wae

There may be some new whizbang method to find a parasitic drain, but the only way I know of is a bit of a process when you've got a vehicle that has approximately 3,725 different fuses spread across 17 fuseboxes in thirteen counties. First thing you'd want to do is pull the negative battery cable and then let the battery get fully charged. Then set your multimeter to show amperage and connect one lead to the negative battery terminal and the other to the negative battery cable. There's a bit of a "boot up" process where you're going to see some draw for a bit, but it should settle down after a little while. You'll want to have the door closed and key removed (from the area, if keyless go) while you're doing this check. Once it settles down, you want to verify that you're getting a draw - a few milliamps is what you'd expect but if you're draining the battery overnight, you're going to be looking at several amps of draw. Once you've confirmed that you've got a draw on the battery where none should exist, the hard part begins. At each fusebox you're going to pull each fuse out and check your multimeter. If the amperage draw doesn't change significantly, then that circuit is okay. If it does, then it's time to break out the wiring diagram for that circuit and start tracing back to everything on it to find your culprit.

If you don't have an assistant to watch the multimeter for you (or really really long leads with good clamps), the other option, once you've confirmed via the first test that you do have a drain, is to re-connect the battery and then check each fuse individually. You'd do that by keeping the multimeter set to an amperage reading, pulling a fuse, touching one lead to each side of the fuse socket, and then checking the readout on the volt meter to see if you're seeing a high amp draw on that circuit.

Max Blast

Does your dome light go off?

eric_in_sd

Hahaha so much about MB makes me shake my head, muttering "why tho".

Clamp-on DC multimeter! They aren't cheap, because they have to calibrate (they measure the magnetic field created by the flowing current) before measure, but they're one of those tools: Nothing quite like 'em.

Terrific writeup.

I generally put my vehicle on a battery maintainer if I am not going to drive it for more than a day. I ought to measure it, but my impression is standby drain on these things is not negligible.

clb0099

yes..

clb0099

Thank you will definitely try this


QUOTE=wae;8891971]There may be some new whizbang method to find a parasitic drain, but the only way I know of is a bit of a process when you've got a vehicle that has approximately 3,725 different fuses spread across 17 fuseboxes in thirteen counties. First thing you'd want to do is pull the negative battery cable and then let the battery get fully charged. Then set your multimeter to show amperage and connect one lead to the negative battery terminal and the other to the negative battery cable. There's a bit of a "boot up" process where you're going to see some draw for a bit, but it should settle down after a little while. You'll want to have the door closed and key removed (from the area, if keyless go) while you're doing this check. Once it settles down, you want to verify that you're getting a draw - a few milliamps is what you'd expect but if you're draining the battery overnight, you're going to be looking at several amps of draw. Once you've confirmed that you've got a draw on the battery where none should exist, the hard part begins. At each fusebox you're going to pull each fuse out and check your multimeter. If the amperage draw doesn't change significantly, then that circuit is okay. If it does, then it's time to break out the wiring diagram for that circuit and start tracing back to everything on it to find your culprit.

If you don't have an assistant to watch the multimeter for you (or really really long leads with good clamps), the other option, once you've confirmed via the first test that you do have a drain, is to re-connect the battery and then check each fuse individually. You'd do that by keeping the multimeter set to an amperage reading, pulling a fuse, touching one lead to each side of the fuse socket, and then checking the readout on the volt meter to see if you're seeing a high amp draw on that circuit.[/QUOTE]

alx

... or when out of ideas you can go to your friendly mercedes dealership and ask them to flash the rear sam as they are known to drain the battery via the rear hatch lock...

funkypost

Mine was water intrusion (through the defective taillight gaskets that were installed at the factory that Mercedes-Benz knows about, but refuses to pay out) which caused the rear SAM ($600 just for the part plus $500 to program to your specific vehicle). Other symptoms included rear tailgate not working, fuel gauge not working and an error message on my dash saying taillight was out. Hope this isn't the case with you as all in, diagnostic, both batteries, tailight gaskets, SAM unit, programing and labor was over $2,000!

Max Blast

In most cases battery drain is because the car doesn’t go to sleep - in that there is a signal from a door telling the dam that it’s still open. So the car doesn’t fully shut down.

look at each door sensor and see if one is stuck.
if this easy out isn’t it, then look at why perhaps a signals acquisition module isn’t telling the car to shut down.

Chrome988

I echo the previous comment that this might be your tailgate latch. I had the same issue as you recently on 2008 gl320.
I got lucky. I had the vehicle off, and I was actually in the rear of the SUV, I was trying to remove the fuse for DVD player because I was worried maybe the DVD player was not shutting off. Well, while in the rear near the fuse box, I heard the rear latch kept making a micro locking sound, so the rear latch kept on trying to do micro closing actions every 20 to 30 seconds. The battery drain stopped once I unplugged the trunk latch motor, no more overnight dead battery. I don't exactly know how to fix the issue, some people are suggesting rear Sam software update, which is a pain because I don't really trust my local mb dealer.

Max Blast

yes, I second that. That’s a great write up.

BlackML550

This video which has been posted before will assist you.