Starting function requirements, general points
Circuit 87 (Engine management ON)
Engine OFF
Drive authorization system stage 4 start enable (DAS 4)
Engaged gear range "P" or "N"
Starting, general points
The starter control system in the CDI control unit (N3/9) is responsible for actuation and shutoff of the starter (M1).
For starting, the CDI control unit reads the following sensors and signals:
High pressure fuel pressure sensor (B4/6)
Atmospheric pressure sensor (integrated in the CDI control unit) for detection of the atmospheric pressure
Crankshaft Hall sensor (B70), for the engine speed
Camshaft Hall sensor (B6/1)
Coolant temperature sensor (B11/4)
Alternator (G2), status over the drive LIN (LIN C1)
Electronic ignition lock control unit (N73), "circuit 50 signal" via drive train CAN (CAN C1) from powertrain control unit (N127)
AdBlue® control unit (N118/5), start enable via drive train sensor CAN (CAN I)
Fully integrated transmission control unit (Y3/8n4), gear range via drive train CAN
The CDI control unit actuates the following components to start the engine:
Starter
Fuel injectors (Y76)
Quantity control valve (Y94)
Fuel pump (M3) via the drive train CAN and the ASCU (N118)
Fuel pump actuation
Actuation of the fuel pump takes place both directly and via the drive train CAN by the ASCU ().
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 sensor (B37).
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
When the ignition key (transmitter key (A8/1)) is moved to the start position, the powertrain control unit receives "circuit 50 signal" via chassis FlexRay (Flex E) from the electronic ignition lock control unit and the signal is sent via drive train CAN to the CDI control unit.
The CDI control unit actuates the circuit 50 starter relay (K40/8kH) with 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 Hall sensor and the message "circuit 61 ON" and that the starting procedure has ended via the message "circuit 50 OFF", the driver will then be able to influence the injection quantity and thus the engine speed via the accelerator pedal sensor.
No start enable from the AdBlue® control unit occurs if the AdBlue® tank is empty and the number of permissible engine starts with an empty AdBlue® tank 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 has reached approx. 700 to 850 rpm or after a starting time of 7 to 10 s (depending on coolant temperature), the CDI control unit interrupts the negative activation of the circuit 50 starter relay and thus terminates the starting procedure.
The starting procedure can only be aborted by switching off the ignition.
The starting procedure is inhibited for approximately 1.5 to 3 s before it can be repeated. 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).
Referenced documents
- gf0716p9997orb Overview of system components for common rail diesel injection (CDI)