Starting System: Description and Operation

GF07.10-P-1001MMI Starting, Function
ENGINES 152.9 in MODEL 172.4

Starting function requirements, general points
^ Circuit 87M (engine timing ON)
^ Engine OFF
^ Start enable for DAS Stage 3 (FBI 3)
^ Engaged gear range "P" or "N"

Starting, general points
For starting, the ME-SFI [ME] control unit (N3/10) reads the following sensors and signals:
- LH and RH intake camshaft Hall sensors (B6/4, B6/5), intake camshaft positions for ignition circuit detection
- LH and RH exhaust camshaft Hall sensors (B6/6, B6/7), exhaust camshaft positions for ignition circuit detection
- Coolant temperature sensor (B11/4)
- Crankshaft Hall sensor (B70), engine speed
- Electronic ignition lock control unit (N73), "circuit 50 signal" via the chassis CAN (CAN E)

The ME-SFI [ME] control unit actuates the following components to start the engine:
- Starter (M1)
- Ignition coils (T1)
- Fuel injectors (Y76)
- The fuel system control unit (N118) directly and via the drive train CAN (CAN C) and thus the fuel pump (M3)

The ME-SFI [ME] control unit coordinates the injection and firing order during starting based on the signals from the crankshaft Hall sensor and the camshaft Hall sensors.
The starter control in the ME-SFI [ME] control unit takes on actuation and cutout of the starter

Function sequence for start
The starter control is sub-divided into the following points:

^ Function sequence for start begin
^ Function sequence for start end

Function sequence for start begin
When transmitter key (transmitter key (A8/1)) is moved to the start position, the ME-SFI [ME] control unit receives the "circuit 50 signal" from the electronic ignition lock control unit via the chassis CAN.
The ME-SFI [ME] control unit actuates the circuit 50 starter relay (N10/1kM) with a ground signal. The power contact on the starter relay closes and the starter solenoid switch is supplied at "circuit 50" with voltage from "circuit 30".

Function sequence for start end
Start control is carried out automatically by the ME-SFI [ME] control unit (touch start). This means that once the start process is initiated, switching off "circuit 50" will have no further influence on the start procedure.
When engine cranking speed has reached 400 to 700 rpm, or after a starting time of 5 to 40 s (depending on coolant temperature), the ME-SFI [ME] control unit interrupts the negative activation of the circuit 50 starter relay and thus terminates the start sequence.

The starting procedure can only be aborted by switching off the ignition.