E500 battery discharge problem

[Phillip Jones]

I am chasing a battery discharge problem on my 2003 E500. I have disconnected the power seat modules and the audio gateway. I bought a low current amp probe and i am getting anywhere from a 1.5 to a 2.5 amp draw. I have removed each fuse and relay one at a time but none of them changes it. I am pretty much at a loss as to what to do now. Any ideas?

[Mxfrank]

The most common cause for an unexpected power draw is a weak alternator diode. Try disconnecting the alternator and see if the draw goes away. (Shouldn't need to be said, but the engine shouldn't be running when you do this.)

[Phillip Jones]

Ok thanks i will check that next. I just went back thru every fuse and relay just to make sure. Still getting a drain, sometimes only about .4amps, sometimes as much as 2.5.

[Phillip Jones]

can i get to the connection to disconnect from the engine bay or am i going to have to jack the car up to get to it?

[Mxfrank]

Originally Posted by Phillip Jones

can i get to the connection to disconnect from the engine bay or am i going to have to jack the car up to get to it?

Not sure on that car. There's probably a terminal block near the battery where the alternator lead can be disconnected, otherwise you'd have to remove the B+ connection from the back of the alternator. Maker sure to tape it off to prevent smoke release. Or just stick the end in a plastic bag.

[97 SL320]

If you are using an amp clamp for testing, just clamp the large alternator wire.

Still getting a drain, sometimes only about .4amps, sometimes as much as 2.5.

From reading other posts, CAN bus systems will stay awake for a few minutes then go into sleep mode. This is probably where you are getting the 2.5A draw. The 0.4 A draw is probably your main issue.

[Phillip Jones]

ok i remember there is a terminal block near the battery which has 4 leads if i remember correctly, not sure which one is the alternator but i can try all 4 and see if the leakage goes away, thanks for the input guys, super helpful!!!!

[nulu]

There is a part called a lower control panel, fuse in in left side of dash, I believe a 5 amp fuse, ive had several e500 have that cause a draw, drink spilled into shift wood area may be the cause fyi, YOU MUST WAIT ATLEAST 20-30 MINUTES BEFORE THE CAR GOES TO SLEEP AFTER REMOVING FUSE, draw ranges from 27-40 ma om average

[97 SL320]

Originally Posted by nulu

There is a part called a lower control panel, fuse in in left side of dash, I believe a 5 amp fuse, ive had several e500 have that cause a draw,

I wonder if this is a shipping fuse. Some cars have a fuse that disables many functions to conserve battery during shipping / storage.

[Phillip Jones]

i have been getting a message that my teleaid was defective. But it has done that since i bought the car a year ago. and only a month ago did it start this discharge problem. A mechanic told me that that can cause a battery drain. Has anyone else heard that?

[97 SL320]

I've had capacitors on various cars fail / leak causing all sorts of issues. One was a fuel pump relay that sensed the ignition tach signal to control the pump. Sometimes the pump would turn on and run the battery down. The leaking cap made a conductive path on the circuit board and turned the relay on.

[Phillip Jones]

After giving everything time to go to sleep i am getting a .15 amp draw. I disconnected the alternator but the draw is still there. Is that enough to kill the battery overnight?

[raymond~]

i've not seen where the battery was verified to be in good health within this thread. that
means good specific gravity and fully charged, as well as voltage reading during high
load such as cranking. the .15a is minuscule but if the power source is already on the
weak side, it could be enough

[oldsinner111]

just unhook it,old car anyways

[Phillip Jones]

brand new battery in trunk and auxilary one as well. Both holding full charge. I am going back thru the fuses and relays making sure that everything is asleep. I have determined it is for sure not one of the ones in the trunk. Working on the passenger compartment one this morning. Just pulling a fuse sometimes wakes it up it seems. If i don't find it this go round i will just connect the trickle charger to it at night and forget about it. I like to fix things whenever i can.