Overview
This document contains information on:
General
Function requirements
Function
General
The engine starts automatically when the accelerator pedal is actuated or the brake pedal is released.
Function requirements
Ignition ON (circuit 15)
Engine management ON (circuit 87 M)
Outside temperature between -10 and 40 °C
On-board electrical system battery temperature 0 to 60 °C
System diagnosis complete and fault-free
Function
The automatic starting procedure takes place when the engine is in automatic stop and the ignition is still switched on.
An automatic starting procedure takes place under the following conditions:
The clutch pedal is actuated (manual transmission)
The brake pedal is released (when the HOLD function is not active and the transmission position is D or N (automatic or dual-clutch transmission))
The accelerator pedal is actuated (automatic or dual-clutch transmission)
The drive program is changed (automatic or dual-clutch transmission)
Vehicle starts to roll
The temperature in the vehicle interior goes outside the selected range
Air conditioning switched on
A voltage dip limiter on the positive pole of the on-board electrical system battery delays the voltage drop during the automatic starting procedure. The starting procedure ends once the engine reaches 400 to 700 rpms.
The voltage dip limiter is an electrically switchable series resistor used to reduce the high power consumption of the starter when the engine is cranked. The voltage dip limiter is connected to the starter circuit 50 relay (M) via circuit 87. When the engine is started, voltage is supplied to the voltage dip limiter. This helps it recognize the starting procedure and activate the series resistor. If the on-board electrical system voltage drops too much due to the high power consumption of the starter, the voltage dip limiter switches the series resistor off.
If the voltage drop at engine start is too large (U < 11 V), an automatic engine stop is not permitted for one minute so as to allow recharging of the ECO start/stop function auxiliary battery. The ECO start/stop function auxiliary battery is only switched in when the on-board electrical system voltage is high enough (U > 13 V). It is disconnected again when the alternator management is active or the on-board electrical system is severely overloaded.
The start/stop unit operates using starter-assisted direct starting. After the engine stops, the crankshaft angle in the rest position is stored in the combustion engine control unit using the crankshaft angle sensor. When the engine starts, synchronization of the fuel injection system and the ignition system that is otherwise required is no longer necessary due to the stored crankshaft angle.