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

Engine 276.8 in model 213, 238

up to model year 2021

Ignition, general points

The partial function ignition describes the behavior of the engine management in ME-SFI [ME] control unit (N3/10) for first switching on of the ignition, for which the engine is prepared for starting, and for switching off of the ignition, for which first 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

Chassis 30

Function sequence for ignition ON

Upon switching on the ignition the engine compartment terminal 15 relay (K40/8kG) is switched on by the electronic ignition lock control unit (N73) via the interior CAN (CAN B).

The signal "circuit 15 OFF" is transmitted redundantly via chassis FlexRay (Flex E), powertrain control unit (N127) and drive train CAN (CAN C1) to the ME-SFI [ME] control unit. The engine compartment circuit 15 relay forwards the on-board electrical system voltage from "circuit 30" to "circuit 15".

If a voltage is applied to the ME-SFI [ME] control unit at "circuit 15", the engine circuit relay 87M (K40/8kN) is actuated by means of a ground signal. This causes the relay to close its power contact and the voltage is forwarded from "circuit 30" (dependent on the respective fuses) as "circuit 87 M4" to the ME-SFI [ME] control unit and as "circuit 87 M1/2/3" to the respective sensors and actuators of the engine management.

If a voltage is present at "circuit 87M", the engine management is switched on and an output stage driver in the ME-SFI [ME] control unit takes over actuation of the engine circuit relay 87M.

The ground connection "circuit 31" takes place from the on-board electrical system battery (G1) over the battery ground point (W10) and over a number of ground lines to the left major assembly compartment electronics ground point (W16/5).

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 via the drive train CAN (only the first time the ignition is switched ON after the vehicle is unlocked).
In the instrument cluster (A1) the engine diagnosis symbol is actuated for a symbol check over the drive train CAN, powertrain control unit, suspension FlexRay, electronic ignition lock control unit and the user interface CAN (CAN HMI).
The throttle valve actuator (M16/6) checks its return spring (over actuation of the throttle valve actuator motor (M16/6m1)) and performs a positioner adaptation (position determination of the throttle valve via actual value potentiometer 1 and 2 (M16/6r1, M16/6r2)).

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 diagnostic CAN (CAN D), electronic ignition lock control unit, chassis FlexRay, powertrain control unit and drive train CAN 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 (Research- Octane Number))
Mixture maps for enriching the fuel/air mixture in different operating states
Basic setting for idle speed
Idle speed for engaged gear range
Fault setting conditions for smooth running detection
Temperature correction for switching fan motor (M4/7) on and off

Function requirements for ignition OFF, general points

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

Function sequence for ignition OFF

For ignition OFF the circuit 15 engine compartment relay is switched off by the electronic ignition lock control unit via interior CAN and front SAM control unit (N10/6). The signal "circuit 15 OFF" is sent redundantly via the chassis FlexRay, powertrain control unit and drive train CAN 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 fuel injectors for cylinders 1 to 6 (Y76/1 to Y76/6) and the ignition coils cylinders 1 to 6 (T1/1 to T1/6) are switched off and computer run-on is started.

Overview of system components for gasoline injection and ignition system with direct injection

GF07.70-P-9998MND