W212 2011 Estate Aux battery function list? Start Stop paramater list? Start Stop is Not Start Stopping!

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stuboy

Member
Joined
Nov 3, 2006
Messages
48
Location
Devon
Car
E320 Avantgarde Estate W210 Petrol
Hi Chaps, my start stop is not!
Its a W212 2011 pre face lift.

Many posts on here suggest the Aux battery is responsible for the start stop but on my estate it is at the back of the boot, given the current used by the starter motor I would suggest it has nothing to do with the start stop function other than maybe the control electronics, due to the lack of an enormously fat wire to the starter and the fact the battery is tiddly.

1) Can anyone definitively list the parts the Aux controls on my model?
2) I assume my start stop is not, as my main battery is sitting at about 12.2volts when connected in the car, and it should be 12.6v?
3) Anyone know the list of parameters the start stop looks at before it says yay or nay?

Cheers
Stuart
 
Yo've understood incorrectly the start/stop battery function. It is not providing power to the starter but for the rest of the car while the main battery starts the car.
 
1) Don't know. I searched for this info before to no avail)... Watching with interest.
2) My stop/start died... (no green dash button light or function). Replacing main battery sorted it.
3) Don't know.

Having a car that starts is a bonus...I don't like stop/start...In rural areas I seldom need it - In city driving I want reassurance of instant throttle response. Its okay on M25 jams. I would prefer it to be default off but with option to switch on.
 
I hate this stop/start too,,( one of the many, I think) and as it's on by default, so when starting the car, switching it off is now standard practice, same as putting on the seat belt, and releasing the park brake. And as I live in a rural area, its not really making any savings in emissions. As I mentioned, its on by default and I thought about taking out the switch, and resetting the cable to turn it off permanently, but maybe that would generate more problems than it would solve. I guess some of the more technically / electronically minded posters on here may know of a sure fire way to disable it permanently, without disturbing the sleeping giant of the CanBus system?
 
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The most common reasons for Start/Stop not working are weak main battery, weak auxiliary battery, or both.

Sadly, in most cases, the only way to fine out is by replacing the batteries one at a time.
 
There are a multitude of parameters checked including, but not limited to:
  • Starter battery voltage
  • Aux battery voltage
  • Engine temperature
  • Ambient temperature
  • Cabin temperature vs desired cabin temperature
  • Humidity (potential for screen to mist if aircon switches off)
As a first call, I’d be inclined to hook a charger maintainer up to the charging posts (it will charge both batteries that way) and then try the car out immediately after everything is fully charged. If stop/start works ok then it’s pretty much a certainty that one or both of the batteries need replacing.

Other than that, you’ll need to get any codes read on Star. One of my E63's had an issue with stop/start not working that turned out to be the gearbox auxiliary oil pump not maintaining full pressure. You’d never have found that without proper diagnostics.
 
I'm going for a new battery first, the dashboard reports the old one as 12.0 volts this morning and it had a long run out yesterday. Will report back when the new one arrives and is fitted ;-)
Stuart
 
I replaced the aux battery on mine and it made no difference, but onchecking my main battery is at 12.2vso I am guessing the system doesnt activate the stop start function due to a below threshold standing battery voltage being to low. My car starts fine on the main battery as it is so I am just going to run mine without the stop start function.
When it no longer starts the car I'll replace it. But I would be interested to see if replacing your main battery sorts the issue.
 
I hate this stop/start too,,( one of the many, I think) and as it's on by default, so when starting the car, switching it off is now standard practice, same as putting on the seat belt, and releasing the park brake. And as I live in a rural area, its not really making any savings in emissions. As I mentioned, its on by default and I thought about taking out the switch, and resetting the cable to turn it off permanently, but maybe that would generate more problems than it would solve. I guess some of the more technically / electronically minded posters on here may know of a sure fire way to disable it permanently, without disturbing the sleeping giant of the CanBus system?

The c class and e class had a 7.5 amp fuse ontop of the small battery . I removed it on the w204 without issue to stop the stop start working. The newer e350 didn't like it though , telling me there was a problem with the aux battery.
 
I have an issue with the start/stop not working on my car unless I'm on a long journey (2-3 hour run), then I see it activated on my dash when I stop in traffic. On shorter journeys it never works!
This could be because the batteries get a good charge. I was considering replacing my aux battery because someone mentioned that it my fix my (no volume) issue on my audio 20 stereo. Having checked the battery, charge with the engine off for 3 hours, the voltage sits at about 12.8, it's on the original Mercedes battery and the car is 10 years old. I guess I should also check the standing voltage of my main battery. Does anyone know what the voltages should be for both?
 
As mentioned in some of the older posts in this thread, many owners do not even use it. I, like others once the engine has started, turn the system off before selecting gear. More trouble than it is worth.
 
You should see well above 12v when measuring battery voltage first thing in the morning after the car was left parked overnight.

At 10 years old, replacing the main starter battery will almost certainly resolve the Start/Stop issue.

Having said that, a battery that is no longer good enough for Start/Stop will typically give you months or even years of otherwise good service, so it's your call.
 
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