97 E300 90mA battery drain
 

For the 2 years I've owned the car its had a persistent 90mA battery drain when everything is shut off. I tried to find it a few times with no luck. If the cars sits without being used for a week it starts up fine but the closer it gets to 2 weeks the more likely it is that it won't start. The simple solution has been to hook it up to the charger in the garage if its been sitting for a few days but the rest of the family doesn't seem to care for this car's special needs.

2 dead batteries later I gave it another shot. Hooked up the amp meter in line with the battery and methodically pulled every fuse I could find 1 by 1. That's all 3 fuse boxes plus the fuses on the K40 relay. I also isolated the alternator, pulled the stereo and unplugged the ECU and TCU and checked the trunk light. No luck, its always pulling 90mA. According to MBcluster it should be pulling 20mA or less with a couple of months worth of reserve between starts.
https://youtu.be/yAf9I12XAzg


I have isolated the drain to the large gauge wire going forward from the battery, not the multitude of orange wires going to the rear fuse box. I also isolated the + terminal on the inner fender with no luck.

This isnt a huge issue but its getting annoying now that we're putting most miles on the other cars. I appreciate any fresh ideals or potential problem spots on the w210 I might have missed.

Thank you

Good analysis and description. My '96 E300D indeed pulls about 20 mA when "off." Have you disconnected the alarm and/or the remote/keyless entry circuits? Since they need to be active at all times, they may not be fused.

Jeremy

A 90ma draw isn't enough to drain your battery in two weeks. Maybe two months. (I just did the math: 53 days, assuming a 100AH Group 49 in good shape. A 20ma drain would give you eight months.) There must be a larger drain.

Is the car locked when the battery drains? It could be that the alarm circuit accounts for the draw. Otherwise, it's probably going to be an intermittent problem. Glad I no longer own a 210.

Thats a good question, I don't know. I don't recall seeing a keyless or alarm fuse marked in the dash or engine fuse boxes. Where is the alarm located on these cars? The drain is the same with the car locked or unlocked. Theres an initial 2 minutes after the battery is disconected where it draws 370mA then it drops to to 90mA.
Yes the car is locked but it also drains with the car unlocked. I've never seen or heard the alarm activate on this car. I wonder if its even functional. I'll look into it. Thanks!

I believe the horn part of the alarm is behind the pass frt 1/4 panel. It sure looked like an alarm horn when I had my 1/4 panel off for replacement. Not sure where the guts would be but prob the CANBUS right?

I had this issue with my W210, drove me mad as it was almost draining the battery overnight in some cases (the battery was underspecced for the car when I got it).

Anyway, over at Mercedes source they had a video about how to find the drain using a 12v test light and gradually pulling fuses - worth a watch anyway.

For me I found it to be the rear dome light that was causing the issue (apparently quite common) - pull the fuse for that and see if that works.

The rear end of the car is controlled by the PSE pump. Not only does it do the blow/suck thing for the door locks (and seat cushions if you are lucky) but it also controls the rear dome light and rear defroster.

I know there are stories of spilled drinks, leaks, etc that can cause the circuit board in the bottom of the PSE to short out. Or you could have a stuck relay.

The units were used across the 210 range so they are getting easier to find. Unfortunately it requires the HHT or Xentry to personalize ("version code") it to the vehicle.

Thank you to everyone for the tips. I will unplug the alarm and PSE pump to see if that makes a measurable difference in the drain.

I should add that I installed a 150a alternator from an R230 and added a 4awg wire from the alternator to the + post on the driver's side inner fender so at least my charging system can deal with afterglow and bring the battery back up quicker than stock. We're taking the car up to Tahoe this weekend so it'll see a few cold starts below freezing. Living dangerously.
http://usercontent1.hubimg.com/11710006.jpg

I didn't know this - How does it control the dome light and rear defroster? You mean those aren't either switched like a normal older car or on the CANBUS?

The PSE has a connection to the body CAN bus to perform these functions. I guess MB thought another SAM in the rear was overkill for these functions so they stuck them in the PSE.

Like your pic. I was that kid.

Except I did it by plugging in one of those old school plugs that did not have the finger guard. Fingers slipped across the blades and also I was making contact with the big steam radiators we had growing up in Chi-town. Next thing I remembered was being on the floor on my butt about 6 ft away. I was 4 or 5 at the time. Lived to tell about it and even though I'm around 480 or higher on a regular basis that remains the worst hit I've ever gotten.

Is the body CAN bus the device in the under hood fuse box near the back?

The CAN bus is a twisted pair network. It connects the various modules together.
https://en.m.wikipedia.org/wiki/CAN_bus

For example, when you push the drivers side window down button, you are activating an input in one of the SAM (signal acquisition module) behind the dash I believe. You are actually switching a resistor on a sensing line. Each button has different resistor values so the SAM looks at the sensing line and based on the voltage on the line determines the function desired.

The SAM puts out a message on the body CAN bus that the driver window should go down. The door module sits on the body CAN bus and picks the "driver window down" request out of the stream of commands going by on the bus. The motor gets switched to drive down the glass.

There are two buses on the 210, body and power train.

You had an encounter with the power train CAN bus with the issue you had with the glow plug relay a while back. 210 glow plug relay is not like a 123/124/126 where it gets a signal from the key switch, on the 210 a CAN bus message commands the glow plug relay on and then monitors the status.

My best advice is to find a shop that has an MB canalyzer. Its a diagnostic tool that can read what's going on over the CAN bus. It will be able to tell you if it is a CAN related draw or not and that will go a long way towards finding the problem.

Looks like the power seat modules can also cause a drain.
http://www.benzworld.org/forums/w210-e-class/1333267-battery-drain-caused-seat-control-units.html
Aparently a common problem on W203s as well which share this component.