Keyless GO discharges car battery? - Mercedes-Benz Forum

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post #1 of 4 (permalink) Old 09-25-2014, 11:03 AM Thread Starter
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Keyless GO discharges car battery?

Car: 2014 E350 4Matic Sports 8K miles

Symptom: Car battery completely dead. First time ever for me using keyless ignition since 2007. First car: Infiniti M35x.

Possible cause (dealer theory): we have SmartKey fob in our pocket, we park car, push Keyless Go Start/Stop button once to switch off ignition. OK fine. Then, if we inadvertently push Start/Stop again, car's power is turned on (equivalent to position 1 when SmartKey is inserted in slot). We exit car with fob in pocket. We're now well outside the operating range of the SmartKey and the car.

Left in this state, dealer is saying power will stay on indefinitely until car battery is completely drained. Roadside Assistance jumped the car & it was fine through several on/off cycles over several days. No "check engine", or "battery" warning lamps ever.

Decided to take it in b/c it did not make sense Mercedes would design a car in this way, especially after reading the owners manual & finding nothing on the topic. The only related item I could find had to do with interior lights. It says, if you switch on one of the reading lights, it will automatically be turned off "after some time" in order to prevent the battery from being discharged, unless you leave the SmartKey in the car's ignition lock slot & have it turned to position 2.

Mercedes dealer service doing a brain dump of the on board diagnostics etc & sending to Mercedes to see if that sequence of events led up to the low voltage codes seen on the OBD scan, leading to battery drain.

Any thoughts?
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post #2 of 4 (permalink) Old 09-28-2014, 04:06 AM
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The Dealer theory on FOB distance is completely silly.
My vote is something was left on, map light, interior light or something and it drained the battery down.

I'll be frank here, there are so many gadgets on these new cars, it's hard to figure out how to simply turn on / turn off
a cabin light! Seriously.

I doubt with all seriousness you will find any code that will show where the power drain emanated from.
I will bet you two Euro's MB Dealership does replace something real expensive, under warranty and the problem goes away!

Anyway, I am looking forward to what your Dealership analysis reveals....

Please post here what happens...

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post #3 of 4 (permalink) Old 09-28-2014, 09:25 PM Thread Starter
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Dealer said they shipped the data dump to Germany. I actually hope it is something stupid that I did, not some random electronic intermittent fault.Yup, then they replace something very expensive & call it a day.

A forum member in my dup post in the sedan W212 forum said be believed the current dealer theory.

The thing I find interesting is the owners manual: it says, if you leave an interior light, like a reading light, on after Keyless Go Start/Stop button ignition shut off, the lights will be turned off "after some time" to prevent battery discharge.

Yet, for something fundamental, like accidentally pressing Start/Stop twice, it leaves the power on indefinitely without warning?????. You would think at the very worst, the car would discharge the batt, but, throw a very specific code to the OBD, set the Check Engine light, so you take it in after its jumped & the then dealer can explain the doofus owner error.
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post #4 of 4 (permalink) Old 09-28-2014, 10:52 PM
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I will not even start long experience how the programmers MB is using made idiotic programs for those cars, but the above theory should be easy to check.
Do the button push, walk the key away and come back without it to check if the cluster displays are lit on.
It takes lot of draw to discharge car battery overnight, so it has to be more than reading light.
Over 20 years ago my friend had mysterious battery discharge on his VW Bug. It would start the engine early in the morning, but not at noon.
Finally the winter has arrived and walking in the morning to the car covered with snow he noted the rear window had snow melted....

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