Eco stop/start

[alanjm99]

Out with the meter today main battery 12.3, running 14.4, car has been sat for the last four days, will give it a run tomorrow and retest... lol still cant find the aux battery

 

[SteveFromAvantgarde]

There are about 3 software updates and patches all for eco stop start issues.

 

[SteveFromAvantgarde]

Out with the meter today main battery 12.3, running 14.4, car has been sat for the last four days, will give it a run tomorrow and retest... lol still cant find the aux battery

Its in the boot, under a cover on the right hand side.

 

[alanjm99]

Its in the boot, under a cover on the right hand side.

Spent an hour this morning searching still cant find it lol

 

[sjmaxwell]

The main battery has a massive influence on the stop start, I went through two in six months!!

 

[Azaerius]

Out with the meter today main battery 12.3, running 14.4, car has been sat for the last four days, will give it a run tomorrow and retest... lol still cant find the aux battery

I would still take it to a specialist (way cheaper than a dealer!) and have them connecting it to diagnostics because I measured my voltages and all seemed OK like with yours but their readings were 10.8v while I was reading 12 to 14v. They swapped both batteries and boom! All working perfectly now!

 

[alanjm99]

Just spoken to PCS, need the battery tested under load, they also advised that the aux battery should be in the boot... if it has one..!!!

 

[Azaerius]

Mine is in the boot under the boot carpet to the right of the tyre inflating stuff.

 

[markjay]

Mine is in the boot under the boot carpet to the right of the tyre inflating stuff.

Mine is in the boot under the boot carpet to the right of the spare tyre.

 

[14emerc]

Don't really like the stop/start but understand why it's fitted. I also switch it off 99% of the time, use it in traffic jams and last summer in a jam, switched it on. I found that after 5mins approx, the engine restarted its self. Had only the radio on and as it was day time , no need for lights. So, not very impressed with S/Start but happy that the ECU saw a need to restart the engine, I expect it saw low volts in the battery.

 

[alanjm99]

Just found the aux battery, put the meter on it 12.4.....will charge both batteries over the weekend, if that doesn't resolve the issue next step will be a load test

 

[sjmaxwell]

Don't really like the stop/start but understand why it's fitted. I also switch it off 99% of the time, use it in traffic jams and last summer in a jam, switched it on. I found that after 5mins approx, the engine restarted its self. Had only the radio on and as it was day time , no need for lights. So, not very impressed with S/Start but happy that the ECU saw a need to restart the engine, I expect it saw low volts in the battery.

You said it was summer so probably had ac running


Sent from my iPad using Tapatalk

 

[14emerc]

No. Had just driven 50+ miles down in Cornwall and then at a stand still on A road. I have a soft top so no need for a/c. I kind of think the main battery was never 100% from new. Here's the thing, you sit with the s/start active and at and in the stop position, you don't expect it ( the engine ) cut-in when you are stil stopped. It's just something I'm now consider.

 

[CowleyStJames]

One of my first things when I start the engine is turn off stop start.
Annoys the hell out of me

 

[Deleted member 65149]

I'm rarely aware of when the start/stop is doing its thing on my car so I leave it alone. I suppose the decent sized V6 petrol engine is so smooth and quiet it's only the rev counter that gives it away that the engine has stopped. And restart is instant with immediate power and no jolt, so again not an issue. The same thing on a brand new diesel Audi A4 I hired in Spain last year was a different matter, noticeably cutting in and out far too often - so I can understand why some people don't like it.

 

[LegionRider]

Had the same problem with my 2012 B180cdi, until I replaced the battery, one very expensive gell battery later the eco system now works every time, It would appear that it will not operate with low battery voltage or amps available to crank the engine

 

[Bobclive2]

Had the same problem with my 2012 B180cdi, until I replaced the battery, one very expensive gell battery later the eco system now works every time, It would appear that it will not operate with low battery voltage or amps available to crank the engine

How I believe it works, the ECU controls the smart alternator via the negative rail battery sensor on the main battery, the ECU reads via the sensor the battery State Of Charge and allows it to go down to around 80%, this is to allow room for any overrun or brake regen to occur at a high charge rate without damaging the battery, this is why a little used or older battery which still has years of life left appears not to hold a full charge, unless there is ample opportunity for regen to occure the main starter battery is rarely anywhere near fully charged. If the battery reaches a SOC of near 100% the CPU stops the alternator putting any further charge into the battery until the SOC of battery is again down to around 80%. Don`t change the battery just because stop/start does not work, total waste of money in my view.

I have disconnected the neg rail sensor on my 2012 petrol turbo C-Class coupe, the ECU now does not know the SOC and puts the alternator into a normal default charge of no more than 14.3 volts, the same as if the sensor had failed. I now have NO stop/start which I wanted to get rid of (now never turns green), I have lost the brake hold function but that`s no issue for me as never trusted it, there are no warning lights and everything else works as normal. The car has just past it`s MOT with sensor disconnected, car starts first time every time on the original 7 year old battery. The only reason for the AGM main battery is stop/start and regeneration, with the sensor disconnected there is no regen and no stop/start so an expensive AGM battery is not needed, this type of battery was never provided pre stop/start.

 

[markjay]

So you disconnected the battery sensor so that Stop/Start never kicks-in (i.e. instead of having to disable it by pressing the bottom at the start of every journey)?

 

[190]

How I believe it works, the ECU controls the smart alternator via the negative rail battery sensor on the main battery, the ECU reads via the sensor the battery State Of Charge and allows it to go down to around 80%, this is to allow room for any overrun or brake regen to occur at a high charge rate without damaging the battery, this is why a little used or older battery which still has years of life left appears not to hold a full charge, unless there is ample opportunity for regen to occure the main starter battery is rarely anywhere near fully charged. If the battery reaches a SOC of near 100% the CPU stops the alternator putting any further charge into the battery until the SOC of battery is again down to around 80%. Don`t change the battery just because stop/start does not work, total waste of money in my view.

That's how I understand smart alternators work although I'm not sure about the oft quoted 80% in practice.

I've always been a bit anal about keeping lead acid batteries fully charged so I find this smart charging enough of an irritation that I want to charge the battery in the garage every weekend. It's an 85 Ah battery so 80% would mean it needed 17 Ah to reach full charge (actually more like 20 Ah due to losses). Even allowing for the fact that an old battery won't really be 85Ah, it takes vastly less than 20Ah to reach full charge I'd say more like 4 or 5 Ah at the most. So the 80% figure in my case is more like 90% or higher depending on the batteries real capacity.

 

[Dickie Fix]

Can't remember where I found this excellent explanation by MB called the ECO start/stop function | Service Technology Guide, but at the bottom of page 25 is the useful note:

"In vehicles of model series 117, X156, 176, 246 and W/X 166, the ECO start/stop function additional battery is charged at 200 mA when the engine hood is open and the SAM (N10) detects that it is being charged from an external source."