CDI starting function

The common rail diesel injection (CDI) controls the following functions through the CDI control unit:

 Starter control

 Preglowing

 Start-up glowing

 Afterglowing

 Actuation of the fuel pump with fuel level sensor

 Synchronization of the injection sequence

 Start quantity control

Starter control

Depending on the messages from the EIS control unit, and the electronic selector lever module control unit on vehicles with 722.6 transmission, the CDI control unit actuates the starter through the starter relay integrated with the fuse and relay block.

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Preglowing

Through the Class C (engine compartment) Controller Area Network bus (CAN C), the CDI control unit receives the "circuit 15 ON" message from the EIS control unit and then actuates the glow output stage and the preglow indicator lamp, depending on the coolant temperature. The glow output stage actuates the glow plugs on the positive side.

Start-up glowing

Through the CAN C, the CDI control unit receives the "DAS 3 MS message" and "circuit 50 ON" message from the EIS control unit and, on vehicles with the 722.6 transmission, the selector lever position "P" or "N" message from the electronic selector lever module control unit. The CDI control unit then actuates the glow output stage. The glow output stage actuates the glow plugs on the positive side.

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Afterglowing

After a successful engine start, the CDI control unit actuates the glow output stage according to the coolant temperature. The glow output stage actuates the glow plugs on the positive side.

Actuation of the fuel pump with fuel level sensor

Through the CAN C, the CDI control unit receives the "DAS 3 MS message" and "circuit 50 ON" message from the EIS control unit and, on vehicles with the 722.6 transmission, the selector lever position "P" or "N" message from the electronic selector lever module control unit. The CDI control unit, through the fuel pump relay integrated with the fuse and relay block, actuates the fuel pump with fuel level sensor, which deliver the fuel through the fuel main filter to the Common Rail high-pressure pump.

Synchronization of the injection sequence

To assign the injection sequence correctly to the cylinder concerned, the sequence is synchronized at the first revolutions of the engine. To do this, the CDI control unit needs the signals from the camshaft Hall sensor and from the crankshaft position sensor.

The CDI control unit evaluates the inductive signal from the crankshaft position sensor and the signal from the camshaft Hall sensor, i.e. it uses both signals to determine when cylinder 1 has reached "ignition TDC".

 If the signal from the camshaft Hall sensor is missing when attempting to start the engine, the engine will not start.

Start quantity control

When the engine is started, the CDI control unit calculates the start quantity according to coolant temperature and engine speed, then actuates the quantity control valve, the pressure regulator valve and the fuel injectors.