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Preheat, Function - GF15.20-D-3005TSC

Engine 642.8 in model 907 

G13789790

Block diagram 

Function requirements for preheating, general points 

Preheating, general points 

The preglowing system warms up the engine combustion chambers to the ignition temperature required for ignition of the fuel/air mixture.

IMPORTANT At cold temperatures, the vent line heater element (R39/4) is actuated by the CDI control unit (N3/28). This prevents the crankcase ventilation system from freezing and therefore associated engine damage.

Function sequence for preheating 

The function sequence is subdivided into the following steps:

Function sequence for preglowing 

The CDI control unit receives the "Circuit 15 ON" message via the drive CAN (CAN C) from the powertrain control unit (N127), suspension FlexRay (Flex E) from the electronic ignition lock control unit (EZS) (N738). The CDI control unit reads the engine oil temperature over the engine oil sensor (B408), and through the drive LIN (LIN C1), it then actuates the glow output stage (N14/8) as a function of the coolant temperature, and via the drive CAN, powertrain control unit, suspension FlexRay, EZS control unit and the user interface CAN (CAN HMI) it actuates the preglow (A1e16) indicator lamp in the instrument cluster (A1). The glow output stage then actuates the glow plugs (R9) on the postive side.

IMPORTANT If an error occurs in the preglow system, at the glow plugs, or on the lines, this is shown by the preglow indicator lamp and also stored in the CDI control unit.

Function sequence for start-ready glowing 

Start-ready glowing ensures an adequately high temperature until the engine finally begins to run. If the CDI control unit receives the "Circuit 50 ON" information via the drive CAN, the powertrain control unit, the suspension FlexRay from the EZS control unit, it then continues to actuate the glow output stage for a specific period, irrespective of the engine oil temperature, and this in turn actuates the glow plugs.

After reaching the ready-to-start period temperature of 1,000 °C, the preglow indicator lamp goes out.

Function sequence for start-up glowing 

Start-up glowing is used to stabilize the cold start speed of the engine. If the CDI control unit receives the "circuit 61 ON" information from the alternator (G2) via the drive LIN, the glow output stage is actuated over the drive LIN. The glow output stage then actuates the glow plugs. In this way the first working cycles and the eventual running of the engine are supported.

IMPORTANT The "circuit 61" line is not needed for alternators with an alternator interface. Using the information that the CDI control unit receives via the alternator interface, the circuit 61 signal is simulated in the CDI control unit and output through a ground connection switching output stage (e.g. for the instrument cluster (A1)).

Function sequence for afterglowing 

Afterglowing improves engine running after a cold start and the engine warm-up characteristics.

After a successful engine start, the CDI control unit reads in the engine oil temperature via the engine oil sensor and actuates the glow plugs via the glow output stage depending on the engine oil temperature.

Function sequence for diagnostic glowing 

This function is used to energize the glow plugs to a low temperature level and a system diagnosis is performed. This function is activated during troubleshooting and when the preglow system has been inactive for a long period (no preheating required owing to high ambient temperature).

Function sequence for preheating diesel particulate filter 

The diesel particulate filter glowing function is used to raise the load and to stabilize combustion, and thus to assist regeneration of the diesel particulate filter (DPF). To do this, the CDI control unit receives the message "circuit 50 ON" via the drive train CAN from the powertrain control unit and the suspension FlexRay from the EZS control unit. The CDI control unit then actuates the glow output stage through the drive-LIN.

Function sequence for emergency glowing 

If a problem in communication occurs between the CDI control unit and the glow output stage, so that the glow output stage does not recognize any activity 2 seconds after activation through circuit 87, the emergency glowing function is actuated for 180 s. If communication malfunctions during the glowing process for more than 250 ms, the glowing process is continued for 180 s.

IMPORTANT If a new glow request is not received from the CDI control unit, the emergency glowing is ended after 180 s.

IMPORTANT The fuel filter heater with condensation sensor (R53/4) is switched on or off via the glow output stage. The bi-metal switch switches the PTC heater booster on at a temperature of ≤ -12 °C and off at a temperature of ≤ -6 °C. Due to the PTC characteristics (with a positive temperature coefficient (PTC)), the surface temperature of the heating element is limited to 163 °C.

Electrical function schematic for preheating PE15.20-D-2051-97TSC 
Overview of system components for common rail diesel injection (CDI) GF07.16-D-9997TSC
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