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We're the (humbled) owners of a 2011 Class B Mercedes with an inbuilt ECO start/stop system. As far as I understand this is how it's supposed to work:

  1. Gear in neutral.
  2. Press the brake pedal all the way.
  3. Motor turns "off".
  4. Shift into first gear.
  5. Motor turns back on.

The salesman remarked that the main problem people have with this system is they don't actually press the pedal all the way to the metal. However, we're experiencing that while this system just works at times, it also just doesn't work at other times. More specifically, it tends to work when leaving home and not to work in return trips.

The operating manual is in German since this is a used car, so I'm kind of at a loss. What's going on here?

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They make the manuals in English, depending on your dealer/mech they may give you one; my mom asked and got one (a $200 book) by asking, and that was a 7 year old model at the time. I'd check my manual but the 2006 E class doesn't have this feature – Ben Brocka Jun 24 '12 at 3:17
my vacuum failed under stop start an i had an accident at very low speed.. the engine didnt start then.. – Steve Apr 22 at 12:14

1 Answer

up vote 6 down vote accepted

There are other factors that affect the start stop feature. I am not sure on that exact model but generally the following things will keep the car engine from shutting off:

  • Coolant Temp too high, or too low
  • The engine has not ran for at least two minutes
  • The AC is on and not in the economy mode
  • Low Vacuum
  • Battery charge low
  • High current draw on the 12 volt system (IE defogger, defroster, and windshield wipers all on at the same time)

If one of the above conditions is met it does not allow the start stop feature to work.

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Pardon my asking: what does "low vacuum" mean? – badp Jun 21 '12 at 18:48
2  
@badp Vacuum is used to control things like the HVAC vents, power brakes, various valves and switches used for emission and engine controls. Vacuum is created by the engine running and there is usually a vacuum reservoir that keeps some in reserve to continue to provide vacuum in times of low engine vacuum (IE acceleration) or when the engine is off. When there is not enough vacuum to keep those things working it keeps the engine running until enough vacuum is present – Larry♦ Jun 21 '12 at 19:10

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