Starting, Function - GF07.10-D-1001TSC

Engine 642.8 in model 907 

Block diagram 

Starting function requirements, general points 

• Circuit 87 (Engine management ON)
• Engine OFF
• Start enable drive authorization system stage 4 (DAS 4)
• Engaged gear range "P" or "N" (with automatic transmission)
• Clutch travel sensor, full clutch operation (with manual transmission with code MJ8 (ECO start/stop function))
• Clutch pedal switch (with manual transmission without code MJ8 (ECO start/stop function))
• Clutch pedal switch, upper (with manual transmission without code MJ8 (ECO start/stop function))

Starting, general points 

The CDI control unit actuates the following assembly parts to start the engine:

• Starter
• Pressure regulator valve
• Fuel injectors
• Quantity control valve
• Fuel pump with fill level sensor via the fuel system control unit

The start quantity control in the CDI control unit serves to calculate a specific start quantity at engine start irrespective of the position of the accelerator pedal module.

Function sequence for start 

The function sequence is subdivided into the following steps:

The starter control system in the CDI control unit is responsible for the actuation and shutoff of the starter.

The CDI control unit reads in the signals of the following component parts for starting:

• Engine oil sensor
• Fuel pressure sensor
• Atmospheric pressure sensor, for acquisition of the atmospheric pressure
• Crankshaft position sensor for the engine speed
• Rpm sensor
• Coolant temperature sensor
• Alternator, status
• Powertrain control unit, "circuit 50 signal" from EZS control unit
• AdBlue® control unit with code KP6 (SCR exhaust gas cleaning, generation 3), start enable
• Fully integrated transmission control (VGS) electric controller unit with code G42 (7G-TRONIC PLUS), drive range

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

Function sequence for start begin 

Pressing the start/stop button twice causes the powertrain control unit to receive the "circuit 50 signal" from the EZS control unit. The powertrain control unit then transmits the "circuit 50 signal" to the CDI control unit.

The CDI control unit actuates the circuit 50 starter relay (F152kC) by means of 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".

If the CDI control unit detects that the engine is running via the crankshaft position sensor and the message "circuit 61 ON" and that the starting procedure has ended via the message "circuit 50 OFF", the driver can influence the injection quantity and thus the engine speed via the accelerator pedal module.

With code KP6 (SCR generation 3 exhaust gas cleaning) No start enable from the AdBlue® control unit occurs if the AdBlue® container is empty and the number of permissible engine starts with an empty AdBlue® container is zero.

Function sequence for start end 

Starter control is carried out automatically by the CDI 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 the engine cranking speed of approx. 700 to approx.850 RPM or a starting time of approx. 7 to 10 s is reached (depending on coolant temperature), the CDI control unit interrupts the negative activation to the circuit 50 starter relay, thereby ending the starting procedure. The starting procedure can only be aborted by switching off the ignition.

If a start is repeated a blocking period of approx. 1.5 to 3 seconds is waited for after ending the start procedure. This occurs so that the rotating pinion of the starter is prevented from meshing with the toothing on the engine clutch plate (ring gear protection).

Electrical function schematic for starting	PE07.10-D-2701-97TSC
Overview of system components for common rail diesel injection (CDI)	GF07.16-D-9997TSC