Preglowing function

P15.20-0234-76

Design

A1e16 Preglow indicator lamp

B11 Coolant temperature sensor

CAN Controller Area Network (CAN data bus)

N3/8 DFI control module

N14/2 Glow output stage

N73 Electronic ignition switch EIS control module (as of 03/97)

R9 Glow plug

S2/2 Glow/starter switch (up to 02/97)

Key positions:

0 Key can be withdrawn only in position 0

1 The majority of electrical components can be switched on

2 Preglow and drive position

3 Start position

Task

Preheating combustion chamber in order to achieve the required ignition temperature of the fuel-air mixture.

Function

After the ignition key is turned into position "2" preglowing is started by the DFI control module (N3/8). A constant dialog based on a pulse width signal takes place over a bidirectional serial interface between the glow output stage (N14/2) and the DFI control module (N3/8). The glow output stage is actuated by the DFI control module and supplies battery voltage to the glow plugs (R9). The glow period is calculated by the DFI control module as a function of the coolant temperature. During the preglow period the preglow indicator lamp (A1e16) in the instrument cluster comes on. Once the required preglow period has been reached, the indicator lamp goes out.

Preglow indicator

The preglow system is monitored only during the glowing operation for:

 Open circuit
 Short circuit
 Fault in glow output stage

If an open circuit exists, the preglow indicator lamp (A1e16) is actuated for 1 minute, not earlier than after the engine has started or start of engine running.

At the same time the fault is stored in the DFI control module (N3/8).

If any of the following faults exists, the preglow indicator is actuated immediately and constantly and the faults are stored in the DFI control module (N3/8):

 Fault in communication

 Fault in glow output stage

 Short circuit of one or several glow plugs

Once o.k. is recognized the fault is no longer displayed but remains stored in the fault memory.