Vlad-II

Hi Everyone!

I drive a 2014 Mercedes C300 with about 57K miles on it. Was wondering since the car is nearing on 7 years old and the batteries haven't been replaced, should I look into replacing the batteries to see if whether or not the ECO START/STOP will start working again? Mine hasn't worked in months. Was wondering what are the steps I can go about to fix that issue. Also I noticed the HOLD functionality does not work sometimes too. So I've been reading about it, apparently the Auxiliary Battery is the source of the power for the HOLD and ECO START/STOP is this right approach?

Best,
Vlad

Gazwould

Auxiliary has nothing to do with brake HOLD , I should know because I've done this..



Why do you want such a ridiculous device to work ?




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Vlad-II

Oh wow seems like you are against it, haha. I mean many new cars have it now, and if the car is made with it and its not working, to me thats a problem no?

LogicalApex

I had my '14 C300 for 90K miles and sold it last year to move to another brand. I had zero issues with Auto Start Stop and I'm not sure why it gets so much hate honestly...

When I had issues with Brake Hold sometimes becoming unavailable it was due to the main vehicle battery. Once I had that swapped it all went back to normal. So I'd start with that first.

When I had the battery swapped I used BMW Roadside Assistance to do it. When done that way they don't charge labor so it was much cheaper than the dealer if you're doing OEM. Also had the added benefit that they changed the battery at my house (was done by a BMW tech).

Tom in Austin

My six year old main battery got an extended charge after a local place tested it and AutoStop works dramatically better now. Suggest you take yours to be tested and give it as much charging as it will take (mine got almost 24 hours worth)

Vlad-II

Yeah the battery is closing in on 7 years old at this point, so I probably should look into replacing it. Is there a way I can test to see if I can get it replaced or check the voltage? I remember reading somewhere that there was a secret menu on the dashboard that I can access or something haha. Also the car is parked a lot during the week, I only drive it during the weekends since I live in the city so I guess that could play a big role with battery charge too I presume. When the HOLD stops working, I usually shut off the engine and start it again manually with my key and it works again but there's no telling when the problem will return.

Mernika

Hello all, my first post here
I am about to replace the aux battery on my 2016 E400 and I looked at he available videos. looks like a straitgforward easy thing but I just want to make sure couple of things. Do I need to disconnect the main battery first or do any other preparations before I start, also, any resets or computer tinkering needed after the new battery is installed? I would appreciate the answers very much !

By the way, my start/stop has never worked since I got the car about 1.5 years ago, but it never bothered me because I'm with those who believe that its benefit is barely noticeable...
Also, probably related to the main battery, but a few months ago my Comand system stopped powering on its own when I start the engine, I have to push the button in the middle of the console, is it because the battery is low and it's trying to save juice, or is it a symptom of some other issue?

Tom in Austin

In my car, disconnecting and removing the main battery to have it tested and charged did not affect anything.

It was a pleasant surprise btw to learn that the signal for the clock comes from the GPS/Nav, so for the first time in my life, I don't have to do anything for daylight savings time, at least not in the Mercedes :-)

Vlad-II

The BRAKE HOLD feature stopped working again. ECO START/STOP hasn't worked since probably late August. So I decided to check the secret menu to get the raw charge levels here's what I got:

ENGINE OFF:
UB: 12.1A and IB: -10.6A

ENGINE ON AND IDLING:
UB: ~14.7 to 14.9 A and IB: ~11.0A to ~12.0A

Based on these readings, it seems like the battery is still okay, despite the car being almost 7 years old at this point. Should I just replace the main battery despite it being I guess what to me looks fine?

Also, Is there a way to test the auxiliary battery to see what the readings are and what they are supposed to be? Is there a way to check the charge level on that?

If I go ahead and replace the Auxiliary Battery, where is it located? I opened the trunk and I did see a battery attached.

Should I look into buying this one from FCP EURO:
https://www.fcpeuro.com/products/mer...300-2115410001

Best,
Vlad

Tom in Austin

You might try putting it on the charger for 24 hours ... discussion elsewhere on here is that Mercedes only charges the battery to something like 80%, presumably to reduce the load on the alternator and perhaps in the process extending the life of the battery too.

A month and a half after giving mine the long overnight charge, I've noticed the ECO re-start is not as smooth as it was. Maybe that means it's fallen back to the 80% range?

Anyway, worth a try if you have a charger and can leave it on the battery for a day.

Vlad-II

I finally took some action today to tackle this annoying issue. I went to AutoZone and they tested both batteries, the main one and the aux battery. The main one was actually listed as "replace" and the auxiliary one tested and it was good.

So that lead me to believe that this issue from the get go might have been with the main battery as some of you guys have pointed out. Perhaps the outgoing main battery was not able to keep a charge or something. I'm not sure how long the Auxiliary Batteries last, but nonetheless, I decided to swap out the main battery today since it was on the list of things I wanted to do with the car anyway. So I called Roadside Assistance, the roadside assistance tech came to AutoZone where I bought the battery and he had assisted me with the battery replacement. The car starts notably much quicker and snappier than before with the older battery. I have still yet to test the Brake HOLD feature haha, but I will test it today and see what happens.

When I drove out of the AutoZone lot with the new battery, the ECO was still yellow; but i'm gonna give it the benefit of the doubt because I didn't drive it much on the new battery, so my assumption is that the new battery has to be charged more. If that still does not work, then maybe the Auxiliary Battery is on its way out as well. The roadside tech who replaced my battery said, if there is no warning light for the Auxiliary battery, then I should not replace it. When I had told the tech who replaced the battery the issue, he advised that the ECO Start/Stop does not work its usually the Auxiliary Battery that should be checked, however that battery looked flawless when I opened it up from the back, so I am gonna give this new battery a good drive and see what happens, and let you all know!

Just204

My start/stop stopped working for a several months before I replaced the original battery last year. If your battery does not have enough reserve energy the feature is disabled. I hate the feature and disabled it, much happier without it.

Vlad-II

ECO/START STOP & Brake HOLD Working. 😊

When in doubt check the battery! Its working perfectly now. 😉. I personally like the ECO system because I live in the city and it is particularly useful for me. Turns out the battery was not ever replaced since 2014 when the car was shipped, so I think it really outlasted itself. 😊

midcityeng

For anyone annoyed with disabling the start / stop feature each time, you can pick up one of our OBD programmers that retains "last mode" for this feature, you can take a look at our vehicle coverages HERE. Pick one up today!

2012 merc amg

Just reviving an old thread. Ya, my Start/Stop has not worked in quite some time. Last time I charged the battery it worked for a couple of days and then went back to not working. Everything else is fine including Distronic and Brake hold. I guess I should probably welcome the fact it does not work as I'm not crazy about it anyhow. Had the main battery tested last night at Batteries plus bulbs and it tested out ok. Resting Voltage is 12.4 volts, drops down to 11.8 volts when cranking and cranks fast. I really don't want to go messing the Aux batt (my car uses the voltage converter buried under the passenger footwell quite yet although the car is 4.5 years old and I've read these things only last 4 to 6 years. I guess I'll follow murphys law on this one since it ain't really broke don't go looking for trouble. Gonna put the maintainer on it today for 24 hours till fully charged and see what happens again. It'll probably work ok for a couple days and then go back to as it is now. Probably if I did replace the main battery it would be ok but I figure why spend the money on one until it absolutely needs one, batteries are not cheap these days.