Starting System: Description and Operation
GF07.10-P-1001OGG Starting, Function
- refinement package
- as of model year 09
Starting function requirements, general points
^ Circuit. 87 ON (engine control ON)
^ Engine OFF
^ Drive authorization system 3 (DAS 3) start enable
^ Engaged gear range "P" or "N"
Starting, general points
The starter control in CDI control unit (N3/9) takes on actuation and shutoff of the starter (M1).
For starting, the CDI control unit reads the following sensors and signals:
- Oil temperature sensor (B1)
- Atmospheric pressure sensor, for measuring the atmospheric pressure
- Crankshaft Hall sensor (B70), for the engine speed
- Rail pressure sensor (B4/6)
- Camshaft Hall sensor (B6/1)
- Coolant temperature sensor (B11/4)
- EIS control unit (N73), "circuit 50 signal" via the engine compartment CAN (CAN C)
- Electric controller unit (VGS) (Y3/8), gear range via engine compartment CAN
The CDI control unit coordinates the injection sequence during starting based on the signals from the crankshaft Hall sensor and from the camshaft Hall sensor.
The CDI control unit actuates the following components to start the engine:
- Starter
- Pressure regulator valve (Y74)
- Fuel injectors (Y76)
- Quantity control valve (Y94)
- Fuel pump (M3)
The fuel pump is actuated via the fuel pump relay (F4kO) on the rear SAM control unit (N10/8).
The start quantity control in the CDI control unit to calculate a specific start quantity at engine start, independently of the position of the accelerator pedal sensor (B37).
Start function sequence
The function sequence is subdivided into the following steps:
^ Function sequence for start begin
^ End of start function sequence
Function sequence for start begin
Through moving the ignition key (transmitter key (A8/1)) into the start position the CDI control unit receives the "circuit 50 signal" from the EIS control unit via the engine compartment CAN.
The CDI control unit actuates the starter relay(F58kI) using 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".
For vehicles with code (U42) BlueTEC (SCR) diesel exhaust treatment no start enable occurs if the AdBlue(R) tank is empty and the number of permissible engine starts for an empty AdBlue(R) tank has been exceeded.
If the CDI control unit detects that the engine is running via the crankshaft Hall sensor and the message "Circuit 61 ON" and that the starting procedure has ended via the message "circuit 50 ON", the driver can control the injection quantity and thus the engine speed via the accelerator pedal sensor.
End of start function sequence
Start control is carried out automatically by the CDI control unit (touch start). This means that if the start process is initiated switching off of "circuit 50" has no further influence on the start process.
On reaching an engine cranking speed of 400 to 700 rpm or a starting time of approx. 5 to 40 seconds (depending on the coolant temperature), the CDI control unit interrupts negative activation to the starter relay and thus ends the starting procedure.
If there is a repeat start after the end of starting procedure, a cutoff period of about 1.5 to 3 s is applied. 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).
