Starting, Function - GF07.10-P-1001MRA

Engine 274.9 in model 205 (except 205.047/053/054/147/247/253) 

Engine 274.9 in model 253 (except 253.354/954) 

Starting function requirements, general points 

• Circuit 87M (Engine management ON)
• Engine OFF
• Drive authorization system 4 (DAS 4) start enable
• Engaged gear range "P" or "N" (for automatic transmission)
• Clutch pedal sensor (B53/1), full clutch operation (with manual transmission)

Starting, general points 

For starting, the ME-SFI [ME] control unit (N3/10) reads in the following signals:

• Intake camshaft Hall sensor (B6/15), intake camshaft setting for ignition circuit detection
• Exhaust camshaft Hall sensor (B6/16), exhaust camshaft setting for ignition circuit detection
• Coolant temperature sensor (B11/4)
• Crankshaft Hall sensor (B70), engine RPM
• Oil level check switch (S43)
• Electronic ignition lock control unit (N73), "Circuit 50 signal" via chassis FlexRay (Flex E), powertrain control unit (N127) and drive train CAN (CAN C1)

The ME-SFI [ME] control unit actuates the following assembly parts to start the engine:

• Starter (M1)
• "Activates" cylinder 1 ignition coil to cylinder 4 ignition coils (T1/1 to T1/4)
• "Activates" cylinder 1 fuel injector to cylinder 4 fuel injector (Y76/1 to Y76/4)
• The fuel system control unit (N118) and thereby the fuel pump (M3) directly and over the drive train CAN

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 subdivided into the following points:

• Function sequence for start begin 
• Function sequence for start end 

Function sequence for start begin 

When the ignition key (transmitter key (A8/1)) is moved to the start position, the ME-SFI [ME] control unit receives the "Circuit 50 signal" from the powertrain control unit via the powertrain CAN and from the electronic ignition lock control unit via the chassis FlexRay.

The ME-SFI [ME] control unit uses a ground signal to actuate the starter circuit 50 relay (K40/8kH) on both sides. 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 

Starter 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 (dependent on coolant temperature), the ME-SFI [ME] control unit interrupts the negative activation of the circuit 50 starter relay and thus terminates the starting procedure.

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

A voltage dip limiter (R62) is installed at the positive battery terminal. Its task is to prevent a drop in the battery voltage below a defined voltage value during the starting procedure of the engine. This is performed through temporary limitation of the starter current. Note here that the battery voltage is only present at the starter positive line during the starting procedure. Before and after the start the starter-plus line must be free of tension otherwise the voltage dip limiter is defective.

	Electrical function schematic for starting		PE07.10-P-2701-97FBA
	Overview of system components for gasoline injection and ignition system with direct injection		GF07.70-P-9998MRA