Turboaction

I thought I'd provide everyone with an update. The system worked properly for about 4 weeks, but the fuse blew again, but this time I could smell something that was a bit like burning electronics in the garage. The car is going up on the lift to see if the rear switching module let the smoke out, or if it's the wiring to the switching module. Either way, I'll let everyone know what the final solution was. It might even be picture worthy.

Turboaction

Ok, so I think this saga is finally complete. And damn, was this ever an adventure. So to recap, the Keyless Go stopped working one day. Replaced the fuse and Keyless Go module, everything worked for about a month. I smelled something like burning plastic, around the same time the Keyless Go stopped working again. The 15 amp fuse would now blow instantly when replaced.

At this point, I know the issue is under the car. I put it up on the lift, and won't you know, the wiring to the rear switching module that detects your feet behind the trunk was broken, melted, and shorted. This was because the wiring was pinched between the steel bumper and the plastic bumper cover. Not only that, but the power and ground wires that feed the rear switching module were melted all the way back to the fuse box and to the chassis ground location (18 ga wire). So... I replaced the power, ground, and signal wires from the source to the rear switching module. I re-routed the wiring above the bumper strut, which appears how it was intended to be in the first place. Now things are working again. However, I didn't try opening the trunk with my foot yet. I wasn't quite ready to awaken the gremlins once again.

On a side note, is there a way to train the car to start in sport mode vs eco mode? My wife is not amused starting in 2nd gear without pushing the E/S button.

Left Coast Geek

noone has figured out how to jigger sport vs econ mode on power on.

fwiw, my e350 is just too twitchy in sport especially at lower speeds, and start in 2nd? pretty sure mine starts in 1st but doesn't' spend hardly any time there. it sure launches off the line fast in E if you give it some gas from a full stop. I'll use S on a twisty mountain road if I'm driving alone and aggressively.

pierrejoliat

MB house in Toronto can reconfigure your car to remember last setting, I don't know where you're located, but it can be done in their shop, so others must be able to do it also. My cars start in second gear in "E"

midcityeng

We have an OBD programmer that remembers your last setting on the engine start / stop function each time you start the car.
It doesn't put it into sport mode, but it does remember that you turned the Eco start / stop function off the next time you start the vehicle.
HERE is the link for it.

silvermoon1959

Secondary battery in trunk may need replacing. This battery runs a lot of the electronics before car is started.
Usually under the spare tire I believe.

bmwpowere36m3

Which car? The auxiliary only plays a role when ECO start/stop is activate on W212s with that feature.

silvermoon1959

I had the keyless go option fail on my 2014 E350. MB replaced the secondary battery under warranty. Problem solved.

Left Coast Geek

thats not true. the aux battery runs all the aux systems, including the stereo and lights, when the engine is being started whether its eco or not. old school cars would shut all that stuff off when being started via a 'load shed' relay, because when the starter is sucking down 200+ amps, they shut off all the extra load so every bit of pookah is available for the starter and fuel injection and ignition. with a modern media player, that would mean a whole reboot of the computer.

bmwpowere36m3

Okay, can you provide some documentation to that effect? I’ve only seen the aux battery for eco models described under the eco system. One of the first items always it what’s required for the eco to be active or enabled.

So if you had a bad or undercharged aux, your assumption is the convenience systems would stumble?

Not exact comparison, but pre-eco models only had a 1.2 ah battery to enable the ignition and shifting in case main battery died. I haven’t noticed any strange behavior when starting...

pierrejoliat

Someone frequently makes all encompassing statements based on the 2016 model, changes were made every year from 2010 on, much on these cars is different, remember the '10 thru '13 only had the small alarm system type battery in the dash, only the '14 thru '16 had the trunk battery. You on the other hand are extremely helpful and I for one appreciate it.

Left Coast Geek

I'm on my phone right now, but that PDF you posted in another thread with the introduction to service for w212, there was a section on the echo on off that showed the operation of the aux battery and the relays in the SAMS and showed a truth table on how they operated, and I'm pretty sure it describes it like I did above

DFWdude

So, the last couple days, my Comand stereo system is not turning on (from last state) when I start the ignition. I've concluded in the past that this means the main battery charge is low.

However, remembering your comments LCG, I decided to try charging the AUX battery, instead of the main battery. I placed the charger on the trunk battery, and turned it on. Instantly it read "FLO" for float charging... meaning the AUX battery is already fully charged. I then hooked the charger to the main battery, and it read 25% charged. So, I've completed a full, 3-hour recharge on the big lug under the hood, and the Comand stereo now resumes when I start the ignition.

My conclusion is that the AUX battery does not power the Comand system. Whatever elso the AUX battery does I have no idea...

bmwpowere36m3

This is purely my understanding of the ECO start/stop and the accompanying auxiliary battery (larger than non-ECO variants).

The purpose of the [larger] auxiliary battery is to buffer a dip in voltage during engine start by supplying power to all active consumers while the main battery is decoupled from the on-board electrical system and is made available solely to the starter. This means active comfort functions are not switched off during starting.

For the ECO start/stop to be "active" there are prerequisites which include: engine running, specific coolant temperature range, vehicle speed exceed threshold once and system diagnosis complete.

With ECO function active and the engine automatically stopped [via ECO function]... when the signal to restart the engine is provided, the front SAM actuates the decoupling relay and the latching relay on the auxiliary battery. The decoupling relay disconnects the main battery from the on-board electrical system and the latching relay connects the auxiliary battery to the on-board electrical system. The onboard electrical system is then supplied by the auxiliary battery.

Once the ECU detects the engine at a certain RPM, the reverse of the above happens and the auxiliary battery is once again disconnected. So in reality, the auxiliary battery is only in play for a few seconds during engine restart. Should really be called ECO Stop/Start...

bmwpowere36m3

What I've noticed on our '11 E350 without ECO...

When you start the car and don't leave it in position II for long, i.e. go straight from position 0 or I to start:

• Command will start booting (no apparent hiccup on screen) and finish soon after the engine has started
• Blower fan "may" reduce during start (hard to tell, set in AUTO, it defaults to slow speed before engine is started and/or warmed up)

Now if you start the car after having left the key in position II long enough for Command to be fully booted and music playing for example:

• Command mutes music during start, but otherwise no hiccups or rebooting of unit
• Blower fan "may" reduce during start (hard to tell, set in AUTO, it defaults to slow speed before engine is started and/or warmed up)

I still need to note what happens with the headlights during a start. The headlights come on when unlocking the car when its dark out (with locator function enabled) and they go out after a period of time OR when a door is opened. I can't remember if they come back on in position II and/or whether they go off/on during a start.

Left Coast Geek

ok, thats different than my 2016 with the bigger batt and eco start/stop. I tend to hook my phone up and push the 'on' button on the stereo system before I even fasten my seatbelt, so COMAND boots, android links up, spotify music starts playing from my phone, then I step on the brake and tap the start button, car starts, and the music and lights don't even flicker. now that I think about it, the headlights don't come on til I hit start and its dark enough. and ok, I'm not sure if they are on AFTER the engine starts or before, because it starts so fast when you hit the button.

ok, just went out and played with it at night in my driveway. when I shut the car off, the headlights dim and off a second later. if the headlights are on auto, when I push-to-start, they do their rise center, adjust thing after the engine is on. but if they are on manual, they come on immediately with the button push... but the engine starts so fast, that by the time the LEDs are at full output, the engine is running.

I should find my cigar plug volt meter/battery monitor, and see if it shows anything change during start. my inner nerd wishes I had a recording meter that could do volt and current measurements over time of each batt during the start cycles, and characterize the whole system. the rest of me keeps the inner nerd in a cage.

Left Coast Geek

oooh, do we know what this speed is? just curious, because a few times eco start/stop hasn't stopped shortly after I rolled out of parking, and this is probably why....


presumably, there's also a mode where when the car is running, and the alternator is running that connects the aux battery to recharge it too?

LILBENZ230

That's odd. I am someone who always keeps the start/stop feature on and I've never had this happen. If I start the car and back out of the driveway, or if I've moved it to wash it and move it back.. the system never activates. So it must be more than a few MPH.

Also, my headlights never come on until the engine starts. Only the DRL strips and parking lights. They light up when unlocked at night, they stay on when I shut the car off to light the way. The headlights run only with the engine. This is with it set to "auto" of course. I don't think I've ever had a Mercedes that worked differently. My W203 and W211 would run the city lights and fog lights when I unlocked at night or after engine shut down. My W204 ran the DRLs and parking lights like the W212.

bmwpowere36m3

8 km/h and yes, based on the auxiliary batteries state of charge, demand on the main battery and status of the alternator.

Paxfobiscum

Secondary battery

PJE

Thanks for prior posts that gave me a hint where to look. My 2015 E250 started intermittently blowing the fuse. I couldn't find the problem. Then it turned into a dead short. Turns out the wire under the rear bumper to the 871 rear foot sensor was badly kinked. It was not pinched like prior poster. But it finally shorted completely. Thanks to earlier poster this was easy to find once I knew to look at it. I cut the wire, separated the 3 conductors and the short vanished. Repaired with good water proof splices and now all good. Hope this helps someone else. BTW, I didn't know I had the 871 foot sensor feature because it never worked. One conductor was probably broken but not shorted from the time I bought the car.