Starting, function

S07.10-0058-79

Starting function requirements, general points

 Engine OFF

 Start enable from drive authorization system

 Engaged gear range "P" or "N" (with automatic transmission)

 Brake pedal actuated (with automatic transmission and with code FX9 (KEYLESS GO)).

 The key is in the vehicle, the key battery is not run-down (with code FX9 (KEYLESS GO)).

Starting, general points

The starter control system in the CDI control unit (N3/28) is responsible for actuation and shutoff of the starter (M1).

For starting, the CDI control unit reads the following signals:

 Engine oil temperature, engine oil temperature sensor (B1)

 Fuel pressure, high pressure fuel pressure sensor (B4/6)

 Atmospheric pressure, atmospheric pressure sensor (integrated in CDI control unit )

 Engine speed, Hall sensor crankshaft (B70)

 Camshaft Hall sensor (B6/1)

 Coolant temperature, coolant temperature sensor (B11/4)

 Status of alternator (G2)

 "Circuit 50" signal, ignition lock switch (S2), without code FX9 (Keyless-Go)

 Start enable via drive train sensor CAN (CAN I), AdBlue® control unit (SCR) (N141), with code MA6 (emissions class Euro 6b N1 GR.III/N2)

 Drive range via drive CAN (CAN C), fully integrated transmission control electric controller unit (VGS) (N15/11)

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

 Starter (M1)

 Pressure regulating valve (Y74)

 Fuel injectors (Y76)

 Quantity control valve (Y94)

 Fuel pump with fill level sensor (M3/3) via the drive CAN and the fuel pump control unit (FSCU) (N118)

 The actuation of the fuel pump with the fill level sensor takes place via the fuel pump control unit (FSCU).

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 (B37/4).

Function sequence for start

The function sequence is subdivided into the following steps:

 Function sequence for start begin

 Function sequence for start end

Function sequence for start begin

Turning the ignition key to "engine start" causes the ignition lock switch to send the "circuit 50" signal to the fuse and relay module control unit (SRM) (N50). The fuse and relay module control unit (SRM) checks the following function requirements:

 Selector level in position "P" or "N" (automatic transmission)

If the function requirements are met, the integrated starter relay (N50k1) will be actuated, which causes the starter to be actuated.

 The CDI control unit determines the start signal status via die signals of the engine speed and the battery voltage.

The starting procedure is interrupted over the fuse and relay module (SRM) control unit. The starting procedure can only be aborted by switching off the ignition.

 For vehicles with code MA6 (emissions class Euro 6b N1 GR.III/N2), no start enable is issued from the AdBlue® control unit 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 starting procedure is initiated, cutout of "circuit 50" will have no further influence on the starting procedure.

When reaching the engine cranking speed of 700 to 850 rpm or a starting time of approx. 7 to 10 s (depending on the coolant temperature), the CDI control unit interrupts negative activation to the starter relay and thus ends 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 s is waited for after ending the starting 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).