Engine control, start/stop function

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The ECO start/stop function is subdivided into the engine-side and the on-board network side scope.
The partial function "engine timing, start/stop function" is viewed in terms of the engine timing system.
Information for partial function "Energy management start/stop function" is documented in the function description "Energy management function".

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Function requirements for the engine timing start stop function, general points

 Engine running

 Outside temperature in the range: -10°C > T < 40°C

 System diagnosis complete and fault-free

 Speed of
8 km/h exceeded once during forward travel

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Engine control, 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 stopping the engine with the vehicle at a standstill.

Switching the engine on and off in a conventional manner using the transmitter key (A8/1) is still possible.

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

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All systems participating on the ECO start/stop function permanently check their status and transmit this via the interior CAN (CAN E) 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 the instrument cluster (A1).

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Engine control, start/stop function, function sequence

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 conditions are fulfilled:

- indicator lamp for the ECO start/stop function button (N72/1s50) lights up (system is fault-free and the ECO start-stop function is activated)

- vehicle speed = 0 km/h

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- coolant temperature >60°C and <115°C

- engine rpm in specified value range

- transmission oil temperature > 10°C and < 120°C

- gear range "D" or "N"

- accelerator not operated

- device brake actuated up to standstill of the vehicle

- 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

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

- coolant temperature sensor (B11/4)

- accelerator pedal sensor (B37), accelerator pedal actuation

- crankshaft Hall sensor (B70) (with direction of rotation recognition), motor rpm

- instrument cluster, vehicle speed via chassis CAN (CAN E)

- Supplemental Restraint System control unit (N2/10), direct crash signal

- Supplemental restraint system control unit via chassis CAN:

- indirect crash signal

- status of driver seat belt

- SAM control unit (N10) via the interior CAN (CAN B) and chassis CAN :

- engine stop prohibition

- engine start request

- engine hood signal closed
- status of the ECO start/stop function button

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- Automatic air conditioning control and operating unit (N22/7) via the body CAN and chassis CAN:

- air conditioning status

- engine stop prohibition

- engine start request

- Electronic Stability Program control unit (N30/4) via the chassis CAN:

- wheel speed
- brake actuation

- engine stop prohibition

- engine stop enable

- engine start request

- left front door control unit (N69/1), front left door contact signal via the interior CAN and chassis CAN

- steering column module control unit (N80) via the chassis CAN:

- steering wheel angle

- steering wheel angular velocity

- DISTRONIC electric controller unit (A89) (for code (239) DISTRONIC PLUS),
engine torque request (increasing or reducing) via the chassis CAN

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- ASCU (N118), fuel pressure via the drive train CAN

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- Fully integrated transmission control control unit for dual clutch transmission (Y3/14n4), status of drive stage via drive CAN

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

After an automatic engine stop a maximum of three

automatic engine stops are permitted without exceeding the speed of 8 km/h.

After the fourth engine start, the vehicle must exceed a speed of 8 km/h for the engine to be stopped again.

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.

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Function sequence of automatic engine start

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 (F58kM) 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 FSCU receives the CAN signal "fuel specified pressure" from the ME-SFI [ME] control unit via the drive train CAN and appropriately actuates the fuel pump (M3) by means of a pulse width modulated signal (PWM signal).

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 Natural gas operation

The automatic engine start takes place in gasoline operation, in order to use the favourable start conditions of the inner mixture formation. Changeover takes place from gasoline operation into natural gas operation during the startup phase.

For an automatic engine stop switchover takes place during a stop process to gasoline operation in order to be able to react to an engine start demand more quickly.

If a leakage in the
gas high-pressure system is recognized during the engine stop phase, the engine is restarted in gasoline operation.

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The engine the remains in gasoline operation until the next automatic engine stop.
If the pressure drop and thus the leakage continue, the engine is again switched into gasoline operation and remains in this until the next ignition sequence.
The natural gas operation is again activated after the automatic engine start if there is no pressure drop.

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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 engine 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 for recognition of rolling backwards

- 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 seat belt buckle for the driver opened or the ECO start-stop function over the ECO start/stop function button is switched off.