Eco start/stop is not working




The ECU logic calculates the charge level of the system battery before enabling Engine Cut Off. ECO remains disabled when general conditions are not met (seat belt, temps, driver door,...)
MB has two charging ports (positive/negative) to connect a battery charger without removing any parts. Sometimes good batteries end up discharged by the car for some odd reasons...
Last edited by CaliBenzDriver; Jun 22, 2022 at 05:08 PM.




You can start dropping parts blindfolded, or you can hook up a scanner and read what is the issue.
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wrong test setup yields questionable data 😳
A nice IR of 8.17Milli-Ohm was calculated which is fairly low (ie. good in this case).
When your car electronics experience extremely low voltage during cranking time, sensitive modules start disfunctioning... then strange things happen afterwards and people call that grumblings because they don't connect related issues.
There are many good things you could do for this car in that order :
- Float charge existing batteries.
- Disconnect battery to soft-reset computers.
- Monitor live battery charge on IC Display while driving.
- Replace badly aged batteries!!
The way both your batteries are acting up at the same time suggest they are not being charged well or discharged while parked or driving.
At the end of the day, another new battery never hurts

Last edited by CaliBenzDriver; Jun 23, 2022 at 05:24 PM.




If replacing the Aux batt doesn't cure your issue, then go for a good AGM main batt. Brace yourself for the price on that one...

Edward




The above PDF describes the role played by the 12AH AUX battery during ECO cycle.
> Basically both SAM's and ECU work together to switch power sources using 2 power relays. At engine restart, AUX gets connected to supply ALL consumers while MAIN is disconnected to only supply the starter. Then switched back around to normal with ALT supplying all power while driving.
> Voltage YoYo?
The really interesting part on page 3 is about switching OFF the alternator :
"If the open circuit voltage (U > 12.5 V) of the additional battery for ECO start/stop function is too low, the alternator's power limit management is deactivated so that the additional battery for ECO start/stop function can be charged"...
"The additional battery for ECO start/stop function is only connected when the alternator's power limit (alternator management) is not active and the on-board electrical system voltage (U > 13 V) is high enough".
The alternator is switched off so the AUX batt does not get hit with a high current jolt of 14.9V when it gets connected for recharge. Once AUX is switched online voltage can get ramped back up. This is the first instance where I see mentioned turning OFF ALT... discharging the main system batt does not exist.
> Rear-SAM takes center stage:
"Following on-board electrical system management information is provided by the rear SAM control unit with fuse and relay module (N10/2):
- State of on-board electrical system battery
- State of additional battery for ECO function
- On-board electrical system status
- Requirements for load-intensive consumers ".
The R-SAM is really stepping up to the plate for power Mgt. This ECO feature requires solid collaboration back and forth from a handful of modules built by different vendors. All these design details help us understand how the distributed firmware is driving these modules.

Last edited by CaliBenzDriver; Jun 26, 2022 at 04:26 PM.




