Ignition, Function - GF07.10-P-1023MRF

Engine 274.9 in model 172.4

as of model year 2017

Engine 276.8 in model 172.4

Ignition general points

The partial function ignition describes the behavior of the engine management in the ME-SFI control unit (N3/10) for first switching on of the ignition, during which the engine is prepared to start and the switching off of the ignition, only after which the engine and then the engine management is switched off.

The function sequence is described in the following steps:

Function sequence for ignition ON
Function sequence for ignition OFF

Function requirements for ignition ON, general points

Circuit 30

Function sequence for ignition ON

When the ignition is switched on, the electronic ignition lock control unit (N73) operating via the interior CAN (CAN B) and the front SAM control unit with fuse and relay module (N10/1) switches on the circuit 15 relay (N10/1kJ). The signal "circuit 15 ON" is sent redundantly from the electronic ignition lock control unit via the chassis CAN 1 (CAN E1) to the ME-SFI [ME] control unit. The circuit 15 relay passes the onboard electrical system voltage from "circuit 30" onto "circuit 15". If a voltage is present on the ME-SFI [ME] control unit at "circuit 15", engine circuit 87 relay (N10/1kN) is actuated by the on-board electrical system voltage.

In this way the relay closes its power contact and the voltage of "circuit 30" is led to the respective sensors and actuators of the engine management according to the respective electrical fuse, as "circuit 87 M1.2/2.2" to ME-SFI [ME] control unit and as "circuit 87 M1.1/1.2/2.2". The "circuit 31" ground connection is made from the on-board electrical system battery (G1) over the front right battery ground point (W10) and over several ground lines to the right major assembly compartment ground point (W16/4).

When the engine management is switched on, the ME-SFI [ME] control unit carries out the following functions:

In order to provide full filling of the fuel low-pressure circuit, the fuel pump (M3) is actuated directly over the fuel system control unit (N118) and also by the FSCU via the drive train CAN (CAN C) (only the first time the ignition is switched ON after the vehicle is unlocked).
In the instrument cluster (A1), the engine diagnosis indicator lamp (A1e58) is actuated via chassis CAN 1, the front SAM control unit with fuse and relay module and chassis CAN 2 (CAN E2) for a lamp check.
Data are exchanged with the electronic ignition lock control unit (circuit 50 signal and drive authorization) via chassis CAN 1.
The throttle valve actuator (M16/6) checks its return spring (by the position of the throttle valve) and adapts the position of the actuator, if necessary.
The fault memory in the ME-SFI [ME] control unit can be read out and deleted via the diagnostic connector (X11/4). The diagnostic connector is networked via the diagnostic CAN (CAN D) with the front SAM control unit with fuse and relay module and via the chassis CAN 1 with the ME-SFI [ME] control unit.

Correction programming or diagnosis can be carried out with the Xentry diagnostics over the diagnostic connector.

Different characteristics maps for the engine management can be stored and activated with the correction programming in the ME-SFI [ME] control unit, such as:

Ignition map for adaptation to various fuel grades (RON correction (R esearch- O ctane N umber))
Mixture maps for enriching the fuel/air mixture in different operating states
Basic setting for idle speed
Idle speed for engaged gear range (for automatic transmission)
Temperature correction for switching on and off the internal combustion engine fan motor and air conditioning system with integrated control (M4/7)

Function requirements for ignition OFF, general points

Circuit 87M (Engine management ON)
Circuit 15 (ignition ON)

Function sequence for ignition OFF

When the ignition is switched OFF, the electronic ignition lock control unit switches off relay circuit 15 via the interior CAN and the front SAM control unit and fuse and relay module. The signal "circuit 15 OFF" is sent redundantly via chassis CAN 1 to the ME-SFI [ME] control unit. If the ME-SFI [ME] control unit receives the "circuit 15 OFF" signal over the engine compartment circuit 15 relay, the engine is switched off by shutting off the fuel pump, the cylinder 1 fuel injector to cylinder 4 fuel injector (Y76/1 to Y76/4) and the cylinder 1 ignition coil to cylinder 4 ignition coil (T1/1 to T1/4) are switched off and computer run-on is started.

The "circuit 31" ground connection is made from the on-board electrical system battery via the battery ground point at the front right and multiple ground lines to the right assembly compartment ground point. When the ignition is OFF, the ME-SFI [ME] control unit is supplied with power from the on-board electrical system battery via "circuit 30 fused".

Electrical function schematic for ignition		PE07.10-P-2723-97TAI
Overview of system components for gasoline injection and ignition system with direct injection	Engine 276.8 in model 172.4	GF07.70-P-9998MNC
	Engine 274.9 in model 172.4 as of model year 2017	GF07.70-P-9998MRE