The ECO start/stop function is subdivided into the engine-side and the on-board network side scope.
The "Engine management, start/stop function" subfunction is examined from the point of view of the engine management.
Information for partial function "Energy management, start/stop function" is documented in the function description "Energy management function".
Function requirements for engine management, start/stop function, general points
Engine runs
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
Speed of 15 km/h exceeded once during forward travel after a maneuvering process
Engine management start-stop function, general
With a stationary vehicle, the 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.
The CDI control unit (N3/9) continuously performs a system diagnosis and assesses the system conditions for the ECO start/stop function.
All of the systems participating in the ECO start/stop function constantly check their status and send this via chassis FlexRay (Flex E) to the powertrain control unit (N127) or via drive train CAN (CAN C1) to the CDI control unit.
If the function requirements are fulfilled, the driver is notified of the start/stop function readiness by the "ECO" symbol in the instrument cluster (A1).
Engine management 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 CDI control unit if all of the following function requirements are fulfilled:
Vehicle speed = 0 km/h
Coolant temperature of 70°C at an outside temperature of -30°C to -10°C
Coolant temperature 60 °C at an outside temperature of –9 °C to 14 °C
Coolant temperature of 15 °C at an outside temperature of 15 °C to 60 °C
Coolant temperature < 110°C
Engine oil temperature in the specified value range
Engine rpm in specified value range
Transmission oil temperature > 10°C and < 120°C
Gear range "D" or "N"
Accelerator pedal not operated
Service brake actuated up to standstill of the vehicle
Atmospheric pressure > 725 mbar
Adequate vacuum (1150 mbar up to 130 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
Fill level in fuel tank > 2 l
Diesel particulate filter system ready
No relevant engine diagnosis concerning the start-stop function or learning functions
Thermal management does not require delayed fan switch off
Fuel temperature between -5°C and 82°C
Exhaust aftertreatment system ready
No relevant errors concerning the start stop function
No previous maximum full-stop braking
For the start-stop function the CDI control unit reads in the following signals:
Engine oil temperature sensor (B1)
Coolant temperature sensor (B11/4)
Accelerator pedal sensor (B37), accelerator pedal actuation
Fuel temperature sensor (B50), fuel temperature
Crankshaft Hall sensor (B70), engine rpm
DPF differential pressure sensor (B28/8)
IC, vehicle speed via user interface CAN (CAN-HMI), electronic ignition lock control unit (N73), chassis FlexRay, powertrain control unit ad drive train CAN
Supplemental restraint system control unit (N2/10), indirect crash signal via user interface CAN, electronic ignition lock control unit, chassis FlexRay, powertrain control unit and engine CAN (CAN C)
Supplemental restraint system control unit, direct crash signal
Status of driver seat belt
FSCU (N118), fuel pressure via the drive train CAN
Fully integrated transmission control unit (Y3/8n4), (with code 427 (7G-TRONIC) or (with code 421 (9G-TRONIC), engaged gear range via drive train CAN (CAN )
Front SAM control unit (N10/6) via interior CAN (CAN B), electronic ignition lock control unit, chassis FlexRay, powertrain control unit and drive train CAN:
Engine stop prohibition
Engine start request
Climate control control unit (N22/1) via interior CAN, electronic ignition lock control unit, chassis FlexRay, powertrain control unit and drive train CAN:
A/C status
Engine stop prohibition
Engine start request
Electronic Stability Program control unit (N30/4) via suspension FlexRay, powertrain control unit and drive train CAN:
Wheel speed
Brake actuation
Engine stop prohibition
Engine stop release
Engine start request
AIRMATIC control unit (N51/3)
Engine stop prohibition
Engine start request
Radar sensors control unit (N62/1), (with code P20 (Driving assistance package)) via drive train CAN from powertrain control unit
Engine torque, increase request
Engine torque, reduction request
Steering wheel angular velocity
Left front door control unit (N69/1) via interior CAN, electronic ignition lock control unit, chassis FlexRay, powertrain control unit and drive train CAN:
Engine stop prohibition
Driver door closed
Steering column tube module control unit (N80) via chassis FlexRay, powertrain control unit and drive train CAN:
Steering wheel angle
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 the engine hood in automatic engine stop, the ECO start/stop function is switched off and all symbols in the instrument cluster light up. The engine must be restarted.
Function sequence for automatic engine start
The engine is automatically started upon releasing the brake or actuating the accelerator pedal.
The CDI control unit actuates the circuit 50 starter relay (K40/8kH) 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 CDI 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 CDI control unit if one of the following function requirements occurs:
On-board network condition requires the engine to run
Coolant temperature > 125°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 (1150 mbar up to 130 mbar)
Driver presence recognition
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 in one the following systems: driver presence, steering, on-board electrical system, brake and management systems, accelerator pedal, transmission, starter, engine, chassis
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 is unfastened or the ECO start/stop function is switched off.
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