stevebez

I decided to make a dedicated thread on this specific drain issue following the first drain source of the leaking batteries in the alarm module was repaired. I have also resorted to using a amp clamp rather than an inline multimeter which are known to be tempremental when reading low current but the unit I got is pretty decent and tallies with the Fluke 117 that I had in line recently. Also I think connecting disconnecting the battery multiple times has not helped the modules throughout the car.

Car has around 300mA drain after 40 mins.

There is zero issue with the front fuse cluster with all fuses reading 0 mA across each of them - so that rules out seat memory modules and door modules.

So the fuse at fault appears to be F003 -> Navigation, Parktronic (PDC) , TPMS, & TV (anything else I may have missed?). I have all these options fitted. Now I have already replaced the Nav and PDC modules. The issue is there is no way to determine if they are good or not from a drain perspective, although they both function perfectly. I had a dodgy front parking sensor that was a bit corroded that I cleaned up and repainted and that seemed to clear the PDC issue that kept throwing false positives. The PDC module I also replaced since the was some evidence of water damage on the old one (it could still be fine though). My old Nav's DVD sensor was a bit flaky so got another dvd drive and so far no issues in functionality. I could get another DVD drive but who is to know of that is faulty too.

Question is has anyone had problems with either the TV module (anyone know where it is?) or the TPMS system causing a drain?

I am also measuring around 42mA draw form fuse F009 -> Roof Unit with car locked and interior sensor on - and this goes to zero if movement sensor is set to off - probably recommended if car is stored in garage for long periods of time.

So disconnected power terminals to Nav drive and removed plugs to PDC and drain remains present of around 300mA

Then I looked for the TV module. I thought it was behind the rear seats on the floor, but found it is actualy the unit above the Nav.

Disconnected the TV module and ... drain gone.

Pulled the unit out and this is what I found... I did see the casing corrosion before but thought this unit was the audio system and not the TV.

Replacement on its way.








So some tips for tracing a parasitic drain in W211's

1). If your battery is toast use a decent battery tester (Topdon AB101 12V Automotive Car Battery Tester) to check it and get a new one or charge it up FULLY.

2). Do NOT use an inline multimeter for amp draw. Controllers get reset each time you connect / disconnect the battery and you cannot reliable readings or cycle the ignition or start the car. Use a multimeter Amp Clamp instead and you dont need to go to town for a Fluke - this one works great it is really good at measuring <1amp draws. (UNI-T UT210E True RMS AC/DC). If you are concerned about draining the battery fit a trickle charger to keep things covered while you trace the issue (I use the C-TEK 7.0).

3). Do NOT pull fuses. This may isolate the issue but once you reseat the fuse it brings the unit back on line and wakes other systems up. Best practice is to measure voltage drop across fuses in mAmps (you will need a decent meter to do so). Zero reading across fuse means there is no current draw. ( I used Fluke 117). See here for a chart to intepret voltage drop readings across fuses (https://www.powerprobetek.com/wp-con...use-charts.pdf).

4). When checking for draw with car locked - leave front driver door and trunk lid open to access the fuses to measure the voltage drop. Make sure the front door latch and the trunk latch are pushed into the latched position (keeping them ajar). You will also need to fashion something to keep the door pin on the driver door depressed (I used a block of soft wood). Turn off the internal movement sensor on the roof unit and lock the car with the remote.

5). Look for water damage / corrosion on any of the units in the trunk, and try your best to keep water out of the trunk. If water does get in, (normally from the trim at the bottom corners of the rear window), make sure things are dried out throughly.

6). Turn off internal movement sensor if car is stored for long periods of time with alarm on - may even be worthwhile to leave alarm off if garaged.

7). Units to check and known issue sources are
a) Alarm siren unit in front wing of car (location varies if you car is LHD or RHD, but it is driver wing you need to look at)
b) Any water damaged control modules in trunk
c) Front seat memory modules
d) Door modules
e) Battery control module. (This will come with other issues too)
f) and most common is fatigue failure of wiring (frayed or broken wires) along the left trunk arm bracket.

C32owner

Great Post. Thanks for sharing glad you got sorted finally.