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Preheat, Function - GF15.20-P-3005OLF

ENGINE 651.9 in MODEL 166 as of model year 2016 

Function requirements of CDI preheating, general points 

Preheat (CDI), 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 (R39/1) is actuated by the CDI control unit (N3/9). This prevents the crankcase ventilation system from freezing and therefore associated engine damage.

Function sequence for preheat (CDI), 

The function sequence is subdivided into the following steps:

Function sequence for preglowing 

The CDI control unit receives the message "circuit 15 ON" from the electronic ignition lock control unit (N73) via chassis CAN 1 (CAN E1). The CDI control unit reads in the engine oil temperature via the engine oil temperature sensor (B1) and then actuates the glow output stage (N14/3) via the drive LIN (LIN C1) depending on the coolant temperature, and the preglow indicator lamp (A1e16) via chassis CAN 1, the electronic ignition lock control unit and chassis CAN 2 (CAN E2). The glow output stage then actuates the glow plugs (R9) on the positive side.

IMPORTANT If an error occurs in the preglow system, at the glow plugs or in the lines, this is shown by the preglow indicator lamp and is 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 information "circuit 50 ON" from the electronic ignition lock control unit via chassis CAN 1, it will continue to actuate the glow output stage for a certain time irrespective of the engine oil temperature, and the glow output stage 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 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 For alternators with an alternator interface the "circuit 61" line is not needed. Using the information received by the CDI control unit through the alternator interface, the "circuit 61 signal" is simulated in the CDI control unit and output via an output stage that switches to a ground connection (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 temperature sensor and actuates the glow plugs via the glow output stage dependent 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 diesel particulate filter (DPF) preheating, with code 474 (Particulate filter) 

The DPF glowing function is used to raise the load and to stabilize combustion and thus to assist regeneration of the DPF. To do this the CDI control unit receives the message "circuit 50 ON" via chassis CAN 1 from the electronic ignition lock control unit. The CDI control unit then actuates the glow output stage through the drive-LIN.

Function sequence for emergency glowing 

If a communication problem occurs between the CDI control unit and the glow output stage, meaning that the glow output stage does not recognize any activity for 2 s after activation via circuit 87, the emergency glowing function is actuated for 180 s. 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.

IMPORTANT The fuel filter condensation sensor with heating element (B76/1) is switched on and off over 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. The PTC characteristics ensures that the surface temperature of the heating element is limited to 163°C.

IMPORTANT PTC

PTC stands for Positive Temperature Coefficient, i.e.: the electrical resistance increases as the temperature increases (PTC thermistor).

  Electrical function schematic for preheating   PE15.20-P-2051-97NBF 
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