n ine S ste
iesel
8
Service Manual – SC8000
Circuit escri tion
For the engine to start:
– The
Key Switch S1
must be set to provide positive voltage to the
Glow Plug Relay K4
, and to the
Relay
PCB
to actuate the engine
Start Relay
and
Run Relay
contacts.
– The
Start Inhibit
relay must not be energized. This means that the
Driver Box
is not providing a ground
to the coil through
J1-22
.
– The drive pedal must be in the neutral position and the
Drive Pedal Sensor
must be in the deadband
range.
For the engine to run:
– The
Ignition Inhibit
relay must not be energized. This means that the
Driver Box
is not providing a
ground to the coil through
J1-34
.
– The
Oil Pressure Switch S28
must be open. This switch is a single-pole, double-throw (SPDT) switch.
When the oil pressure is too low, the switch is in the inactivated state (normally-closed contact is
closed). When there is oil pressure, the switch activates so that the normally-open contact will be
closed. The pressure switch is set at 10 psi.
– The
Coolant Temperature Switch S9
must be open. This switch is normally open, and will close when the
coolant temperature reaches 235 degrees F. When the switch closes, it provides a ground to pin
J1-25
on the
Driver Box
.
