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Preheat, function - GF15.20-P-3005OGG

ENGINES 642.8 in MODEL 164.1 as of model year 2009/AEJ (YoM) 08 model refinement package 

ENGINES 642.8 in MODEL 164.8, 251.1 as of model year 2009/AEJ (YoM) 08 

ENGINES 642.8 in MODEL 251.0/1 as of model year 2011/AEJ (YoM) 10 model refinement package 

Function requirements for preheating, general points 

Preheating, general points 

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

IMPORTANT At cold temperatures the vent line heater element (R39/1) is actuated by the CDI control unit (N3/9). This prevents freezing of the crankcase ventilation system and any 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 from the EIS [EZS] control unit (N73) via the engine compartment CAN (CAN-C). The CDI control unit reads in the engine oil temperature via the oil temperature sensor (B1) and then actuates glow time output stage (N14/3) via the drivetrain LIN (LIN C1), depending on the coolant temperature, and the preglow indicator lamp (A1e16) via the engine compartment CAN. The glow time output stage then actuates the glow plugs (R9) on the plus side.

IMPORTANT If an error occurs in the preglow system, at the glow plugs or on the lines then 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 idle speed is reached. If the CDI control unit receives the "circuit 50 ON" data over engine compartment CAN from the EIS [EZS] control unit, it will continue to actuate the glow time output stage for a certain time irrespective of the engine oil temperature which in turn actuates the glow plugs. After the start-ready temperature of 1250 °C has been reached, the preglow indicator lamp goes out.

Function sequence for startup glowing 

Start-up glowing is used to stabilize the cold start engine speed. If the CDI control unit receives the "circuit 61 ON" data over engine compartment CAN from the EIS (EZS) control unit, then the glow time output stage will be actuated over drive LIN. The glow time output stage reacts by actuating the glow plugs. In this way the first working cycles and the eventual running of the engine are supported.

Function sequence for afterglowing 

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

Following a successful engine start, the CDI control unit reads in the engine oil temperature through the oil temperature sensor and then actuates the glow plugs via the glow time output stage to match 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. It is activated for troubleshooting purposes and when the preglow system has not be activated for a long period (no preheating required owing to high ambient temperature).

Function sequence for DPF glow function, with code (474) Particulate filter 

The DPF glow function is used to raise the load and to stabilize combustion and thus to assist regeneration of the DPF. The CDI control unit receives the message "circuit 50 ON" over the engine compartment CAN from the EIS [EZS] control unit. The CDI control unit then actuates the glow time 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 time output stage so that the glow time output stage does not recognize any activity 2 seconds after activation through terminal 87, the emergency glowing function is actuated for 180 seconds. If communication is missing during a glowing process for more than 250 ms then the glowing process will be continued for 180 s.

IMPORTANT If no new glow request is received from the CDI control unit then emergency glowing stops after 180 s.

REFER TO SYSTEM WIRING DIAGRAMS Electrical function schematic for preheating Model 164 PE15.20-P-2051-97MAA 
Model 251 PE15.20-P-2051-97RAA
  Component description for instrument cluster A1 GF54.30-P-6000GM
  Component description for CDI control unit N3/9 GF07.16-P-6000OGU
  Component description for EZS control unit N73 GF80.57-P-6003GM
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