ECO Start/Stop Function Engine Management, Function - GF07.10-P-1042MRF

Engine 274.9 in model 172.4 

as of model year 2017 

Engine 276.8 in model 172.4 

The ECO start/stop function is subdivided into the engine-side and the on-board network side scope.

The "ECO start/stop function" partial function is seen from the point of view of the engine management.

Function requirements ECO start/stop function, general points 

• Engine runs
• Outside temperature in the range: -10°C to 40°C
• System diagnosis complete and fault-free
• Speed of 8 km/h exceeded once during forward travel

ECO start/stop function, general points 

For a stationary vehicle, the ECO 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 emissions are reduced by cutting out the engine with the vehicle at a standstill.

Conventional cutting out and starting of the engine with the transmitter key (A8/1) or via the KEYLESS-GO start/stop button (S2/3) (for code 889 (Keyless-Go) and the electronic ignition lock control unit (N73) continues to be possible.

The ME-SFI [ME] control unit (N3/10) permanently performs a system diagnosis and assesses the system conditions for the ECO start/stop function.

All systems participating on the ECO start/stop function permanently check their status and transmit this via chassis CAN 1 (CAN E1) or drive train CAN (CAN C) to the ME-SFI [ME] control unit.

If the function requirements are fulfilled, the driver is notified of ECO start/stop function readiness by the "ECO" symbol in the multifunction display (A1p13) in IC (A1).

Function sequence for ECO start/stop function 

The ECO start/stop function consists of the following partial functions:

• Function sequence for automatic engine stop 
• Function sequence for automatic engine start 
• Function sequence for forced engine start (a start dictated by the system) 

Function sequence for automatic engine stop 

The engine is switched off by the ME-SFI [ME] control unit if all of the following function requirements are fulfilled:

• Indicator lamp for the ECO start/stop function button (N72/1 s50) lights up by means of the UCP control unit (N72/1) (system is fault-free and ECO start/stop function is activated)
• Vehicle speed = 0 km/h (for an A/T)
• Vehicle speed < 8 km/h (for a manual transmission)
• Coolant temperature >60°C and <115°C
• Engine RPM in specified value range
• Transmission oil temperature > 10°C and < 120°C
• Transmission in neutral (for a manual transmission)
• Gear range "D" or "N" (for a automatic transmission)
• Clutch not actuated (for a manual transmission)
• Accelerator pedal not operated
• Service brake actuated (for a manual transmission)
• Service brake actuated until vehicle is at standstill (with automatic transmission)
• Adequate vacuum (-1050 mbar up to 90 mbar) in brake booster
• Engine hood closed
• No crash signal
• Steering wheel angular velocity in the specified value range
• Condition of the on-board electrical system OK
• Driver door closed
• Driver seat belt applied
• Interior temperature regulated

The ME-SFI [ME] control unit reads in the following sensors and signals to fulfill the function requirements:

• Coolant temperature sensor (B11/4)
• Accelerator pedal sensor (B37), accelerator pedal actuation
• Crankshaft Hall sensor (B70), engine RPM
• Manual transmission main shifter shaft position sensor (B79/3) (with manual transmission)
• Clutch pedal switch (S40/3), clutch operation (for a manual transmission)
• Clutch pedal start enable switch (S40/5) (for manual transmission), full clutch operation
• IC, vehicle speed via chassis CAN 1, the front SAM control unit with fuse and relay module (N10/1) and the chassis CAN 2 (CAN E2)
• DISTRONIC electric controller unit (A89) (for code 239 (DISTRONIC PLUS)), engine torque request (increase or reduction) via chassis CAN 1
• Supplemental restraint system control unit (N2/10), direct crash signal
• Supplemental Restraint System control unit via chassis CAN 1:
  • Indirect crash signal
  • Status of driver seat belt
• Front SAM control unit with fuse and relay module via the chassis CAN 1:
  • Engine stop prohibition
  • Engine start request
  • Signal that engine hood is closed
  • ECO start/stop function status button
• AAC control and operating unit (N22/7), via the interior CAN (CAN B), front SAM control unit with fuse and relay module and chassis CAN 1:
  • Engine stop prohibition
  • Engine start request
  • A/C status
• Electronic Stability Program control unit (N30/4) via chassis CAN 1:
  • Wheel speed
  • Brake actuation
  • Engine stop prohibition
  • Engine stop release
  • Engine start request
• Left front door control unit (N69/1), front left contact switch signal via the interior CAN, front SAM control unit with fuse and relay module and chassis CAN 1
• Steering column tube module control unit (N80), via chassis CAN 1:
  • Steering wheel angle
  • Steering wheel angular velocity
• FSCU (N118), fuel pressure via the drive train CAN
• Fully integrated transmission control unit (Y3/8n4) (for A/T), status of gear range via drive train CAN

After an automatic engine stop a maximum of three automatic engine stops are permitted without exceeding the speed threshold of 8 km/h.

After the fourth engine start, the vehicle must exceed a speed of 8 km/h in the engine stop.

Upon opening of the engine hood in automatic engine stop, the ECO start/stop function is switched off and all indicator lamps in the IC light up. The engine must be restarted using the transmitter key or over the start/stop button KEYLESS-GO (for code 889 (Keyless-Go).

Function sequence for automatic engine start 

With a manual transmission, the engine is automatically started upon actuating the acceleration or clutch pedal. For an A/T the engine is automatically started upon releasing the brake or actuating the accelerator pedal.

The ME-SFI [ME] control unit actuates the circuit 50 starter relay (N10/1kM) with a ground signal. The power contact on the relay closes and the starter solenoid switch (M1) is supplied at "circuit 50" with a voltage from "circuit 30". The fuel system control unit receives the CAN signal "Fuel specified pressure" from the ME-SFI [ME] control unit via the drive train CAN and actuates the fuel pump (M3) with a pulse width modulated signal accordingly.

Function sequence for forced engine start (a start dictated by the system) 

The forced engine start subfunction is available as a protection function. 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 start requirements occurs:

• On-board network condition requires the engine to run
• Coolant temperature >115°C
• Exceeding of the engine stop period of a maximum of 3 minutes
• A/C required engine running (e.B. windshield fogged up)
• Vacuum on brake booster not in the nominal range (-1050 mbar up to 90 mbar)
• Driver presence recognition (driver seat belt or driver door is opened)
• Change of the steering wheel angle by more than 8°
• Vehicle speed > 2 km/h for forward travel and immediately upon recognition of rolling backwards (for an automatic transmission)
• Vehicle speed >8 km/h for forward travel and for reverse travel (for a manual transmission)
• System or communication error of the following systems: driver presence, steering, on-board electrical system, brake and control systems, accelerator pedal, transmission, starter, engine

A maneuvering process is recognized for an engaged reverse gear and the ECO start/stop function is deactivated. If the engine is stopped it is force started by the system and the engine stop function is suppressed if it is running. The ECO start/stop function is subsequently activated again for an engaged forward gear and for exceeding a vehicle speed 15 km/h.

The engine is also started if the driver door is opened, the driver seat belt buckle is opened or the ECO start/stop function is switched off via the ECO start/stop function button.

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