Current drain. E class W211

[clivec]

Been done to death I know, but here's something unexpected. With my 2008 E320 CDI AvantGarde saloon I have been plagued for years with a constant current drain that proved elusive. MB main dealer and an independent specialist showed the resting drain was below 50mA and shrugged their shoulders - "no fault found." Yet both the original battery and its new replacement still went flat in 7 to 10 days. The car lived constantly on a mains charger, later changed to a solar panel resting on the dashboard. Carried a battery starter pack around in the boot as well, just in case.

Lately, my son bought me a very handy gadget - a battery monitor, made by CTEK, that links by Bluetooth to a mobile phone. It records charge capacity data every 5 minutes which you can download to your phone. So, you can see on your phone a graph of battery charge status over time - for hours, days or weeks. Very handy as it turned out.

At last I could see what was happening - 10% loss of charge per day. The leak always started 2 to 4 hours after the car went to sleep.

I went round unplugging everything I could think of - all the usual culprits, watching what happened to the charge graph overnight. After a lot of unplugging and plenty of patience, it turned out to be the Navigation DVD drive in the boot that was quietly and steadily leaking current to earth, only starting several hours after system shut down. It's staying unplugged. For the first time in years, the battery now stays charged for weeks, without any external charger or solar panel connected.

I'll investigate if it can be repaired or maybe I'll chance a second hand one. I don't know if a replacement would need coding in to the car or not. But regardless, the long term battery drain is gone!

 

[thebiglad]

Hi Clive, first of all delighted to here that the current drain problem has been found and resolved. Secondly this tool/app combo sounds very interesting and useful - do you have further info about it or ideally a link to a supplier ?

Cheers
Dave

 

[clivec]

Hello Dave,

This is the gadget:

CTX BATTERY SENSE

Halfords have them as do Amazon, which is where my son found it.

Saved me a lot of grief as the standard pull-fuses-and-watch method just gave confusing readouts on my clamp meter. The mA current readings were jumping up and down constantly. I now realise all I had to do was stand and watch it continuously all night and all day over a few days! I'd have arrived at the same answer in the end.

This way, the ctek gadget did the watching for me.

 

[thebiglad]

Thanks for that Clive, looks like a really useful data generator, I like it.

 

[Major774]

I might have to do the same test on my car.

I got this battery drain thing that is bugging me for years. I have also done many fuse and relay pulling.

When you went to unplug the modules for testing and then left it over night for monitoring, did you pull the module or the fuses?

 

[Major774]

Looks like I might have a rear sat nav drive problem as well.

Scenario 1
With everything connected I am losing 6-7% of charge per 24 hours.

Scenario 2
With the rear sat nav drive disconnected this drops to a loss of 2-3% per 24 hours. The remaining % I will accept as I know running a electronic lowering module, which has a permanent live feed.

I am going test each scenario once more to check it’s not a fluke.

 

[Justintyme]

Congratulations on solving your battery problem!!! Lovely feeling to finally nail the culprit!! So this gadget was able to inform you immediately when the leak started, and how long it continued but after that, it still needs a bit of detective work to track down the culprit ? How did you match the leaking time frame to the Nav dvd in the boot? Inspired guess-work, or was there something else? In any case, Its a very use full bit of kit.

 

[clivec]

Hello,

Sorry for the slow reply to your question.

Once I got the CTEK monitor up and running and I understood what it was actually telling me, I started unplugging modules (not the fuses) first. I got from this forum a list of the usual culprits and physically unplugged one or two at a time (e.g. instrument cluster and overhead light console) and watched what happened over a few days. This soon told me which modules/units were "innocent", because the steep discharge curve didn't change.

I just kept going, unplugging further modules and watching the CTEK graph over a few days, after each unplugging. Only when I unplugged the dvd drive and the central audio gateway in the boot, did anything suddenly change. The steep discharge curve overnight was replaced by a near-flat line. So I knew I was getting near.

I reconnected the central audio gateway and the navi dvd drive unit and pulled their fuses out instead, one at a time and watched the CTEK graph over a couple of days. Bingo! The problem was gone if I pulled out fuse no 3, 7.5A, in the boot.

I temporarily put in a fibre optic return loop (a few quid on ebay) to bypass the Navi DVD drive and get the rest of the audio system working OK.

There's been a postscript to this long story: I got the culprit Navi DVD drive on the bench and did a simple earth leakage soak test over 48hrs. Nothing found. The resting draw was 1.2mA dropping after a few hours to 0.8mA. I was stumped.

Then I tested the pin-outs. I found a constant 12V output on the pink wire CANBUS pin, which I didn't expect. It was still there 48hrs later. Then I remembered when, days earlier, I'd been pulling the Comand unit and the CD changer out of the dash, the fibre optic cable ends out of both units were repeatedly flashing signals at me even though the whole system was switched off at the Comand knob and the multiplugs for both units were out. I thought this was odd at the time and I certainly didn't understand it.

I now think the Navi DVD drive fault was not a current leak to earth at all, but a different internal fault causing it to constantly wake up via CANBUS the rest of the system and thus consume power that way. I'm certainly no expert but that fits my observations. From the discharge curves on my smartphone, the current was considerable. I estimate 500-750mA - easily enough to flatten the battery in 10 days, which is exactly what was happening. But, in each overnight test, the current drain always took 3 or 4 hours to appear after the initial shut down.

I pondered a new or secondhand replacement DVD drive as I couldn't find anyone willing to repair these. In the end I took the cheapskate option of rewiring the power feed to fuse no 3 (7.5A). It's now on an ignition feed and no longer on constant 12V battery voltage. The Comand and Navi system work perfectly and the battery is holding up brilliantly for the first time in years. So, all well so far.

This message is regrettably long, just like the battle to solve this. I hope the detail I've given helps someone else. Good luck.