Computers and Control Systems: Description and Operation

GF07.10-P-1040MMC Engine Start-stop Function
- ENGINES 157.9 in MODEL 216.3, 221.0 /1
- with CODE (B03) ECO start/stop function
- ENGINES 278.9 in MODEL 216.3, 221.0 /1
- with CODE (B03) ECO start/stop function

Function requirements the engine start-stop function, general points
- Engine running
- The speed threshold (v = 8 km/h) is exceeded once
- Gear range "D" or "N" engaged

Engine Start/stop function, general points
For a stationary vehicle, the engine Start-Stop function switches the engine off automatically and starts it again, as soon as the driver wishes to drive off. The fuel consumption and thus the exhaust emission are reduced through cutting out the engine for a vehicle standstill.

Conventional cut out and starting of the engine with the transmitter key (A8/1) or via the Start/Stop button KEYLESS-GO (S2/3) (for code (889) Keyless Go) continues to be possible.

Through use of ECO start/stop function 12 Ah additional battery (G1/13), the voltage drop is buffered during an engine start. The additional battery takes on the power supply for all active consumers while the on-board electrical system battery (G1) is decoupled from the on-board electrical system and is exclusively available for the starter (M1).

The ME-SFI [ME] control unit (N3/10) performs an SD immediately after a cold start of the engine and assesses the functionality of the engine start/stop function.

The front SAM control unit with fuse and relay module (N10/1) also checks the function of all relevant components for isolating the on-board electrical system battery and connecting the additional battery for the ECO start/stop function.
The engine start/stop function is activated after starting the engine.

For the start-stop function the ME-SFI [ME] control unit reads in the following sensors and signals:
- Coolant temperature sensor (B11/4)
- Accelerator pedal sensor (B37), accelerator pedal actuation
- Crankshaft Hall sensor (B70), engine speed
- Restraint systems control unit (N2/7), direct crash signal
- Restraint system control unit, indirect crash signal over the chassis CAN (CAN E)
- Restraint systems control unit, status of the driver seat belt via the chassis CAN
- Rear SAM control unit with fuse and relay module (N10/2), engine hood closed signal via the interior CAN (CAN B) and the chassis CAN (for code (551) Antitheft alarm system (EDW)
- AAC control unit (N22/1), air conditioning status via the interior CAN and the chassis CAN
- AAC control unit, engine stop prohibition via the interior CAN and the chassis CAN
- AAC control unit, engine start request via the interior CAN and the chassis CAN
- ESP control unit (N47-5), brake actuation via the chassis CAN
- ESP control unit, vehicle speed via the chassis CAN
- ESP control unit, wheel speed via the chassis CAN
- ESP control unit, engine start request via the chassis CAN
- ESP control unit, engine stop release via the chassis CAN
- ESP control unit, engine stop prohibition via the chassis CAN
- AIRMATIC with ADS control unit (N51), engine start request via the chassis CAN (for code (489) AIRMATIC (air suspension with continuous adjustable damping)
- Video and radar sensor system control unit (N62/2) (for code (233) DISTRONIC PLUS, for code (237) Active Blind Spot Assist for code (238) Active Lane Keeping Assist), engine torque request (increasing via the chassis CAN)
- Video and radar sensor system control unit (for code (233) DISTRONIC PLUS, for code (237) Active Blind Spot Assist for code (238) Active Lane Keeping Assist), engine torque request (reduction via the chassis CAN)
- Left door control unit (N69/1) (for model 216) or DCU at the front left (N69/1) (for Model 221), signal from door contact at the front left via the interior CAN and chassis CAN
- Steering column tube module (N80), steering wheel angle via the chassis CAN
- steering column tube module, steering wheel angular velocity via the chassis CAN
- FSCU (N118), fuel pressure via the drive train CAN (CAN C)
- Electric controller unit (VGS) (Y3/8), status of gear range via the drive train CAN (CAN C)

Function sequence for engine start/stop function
The engine start-stop function consists of the following partial functions:
- Function sequence for engine stop
- Function sequence for forced engine start
- Function sequence for engine start

Function sequence for engine stop
The engine is switched off by the ME-SFI [ME] control unit if all of the following function conditions are fulfilled:
- Coolant temperature greater than 15°C and less than 110°C
- Transmission oil temperature greater than 10°C and less than 120°C
- Fuel temperature greater than 10°C and less than 90°C
- Vehicle speed v = 0 km/h
- Engine oil temperature in the specified value range
- Engine rpm in specified value range
- Gear range "D" or "N"
- Accelerator not operated
- Service brake actuated up to standstill of the vehicle
- Adequate vacuum in the brake booster
- No control intervention function from AIRMATIC, brake assistance and distance regulation system
- Engine hood closed
- No crash signal
- Outside temperature in the range 10 to 40°C
- Condition of the on-board electrical system and additional battery OK
- Condition of the on-board electrical system OK
- Driver door closed
- Driver seat belt applied
- interior temperature regulated

After an automatic engine stop a maximum of three automatic engine stops are permitted without exceeding the speed of v = 8 km/h.
After the fourth engine start exceeding the speed of v = 8 km/h is required in order to come back into the engine stop condition again.

Information for switching off the fuel pump (M3) and for controlling the fuel pressure are described in the following document:
- Fuel supply, function

Function sequence for forced engine start
As a protection function the partial function forced engine start is available. Here the engine is force started autonomously (without any action taken by the driver) by the ME-SFI [ME] control unit if one of the following function conditions occurs:
- Condition of the on-board electrical system battery not OK
- Condition of the on-board electrical system not OK
- Operating temperature of the engine, transmission and fuel outside the function requirements
- Exceeding of the engine stop period of a maximum of 3 minutes
- Changing the status of the A/C
- AIRMATIC, brake assist or distance regulation system in control intervention function mode
- The vacuum on the brake booster is not adequate
- Driver presence recognition
- Change of the steering wheel angle by more than 8°
- Vehicle speed 2 km/h (forwards) and 1 km/h (backwards)
- Communication error for the engine start/stop function with one of the following systems: suspension and steering functions, energy management, brake and control system

A maneuvering process is recognized for an engaged gear range "R" and the engine start/stop function is deactivated. If the engine in engine stop is force started and an engine stop suppressed for a running engine.

The engine start/stop function is subsequently activated again for an engaged gear range "D" and for exceeding a vehicle speed v = 15 km/h.

Function sequence for engine start
When actuating the accelerator pedal the engine is started automatically by the on-board electrical system battery. During the starting procedure the on-board electrical system battery is separated by the on-board electrical system and the voltage dip, which would otherwise be noticeable for the vehicle occupants, is suppressed. The ME-SFI [ME] control unit evaluates all relevant variables and awards start enable to the front SAM control unit with fuse and relay module (N10/1).

Precise information about starting the engine is described in the following document:
- Starting, function

Further partial functions for the engine start/stop function are described in the following document:
- Engine start/stop automatic function