Engine Cranking - jcb JS300 Service Manual

Overview
K Fig 9. Engine Cranking ( T C-72)
(K Fig 8. ( T
C-71))
To enable engine cranking (operation of the starter motor),
the engine stop switch (C119) in the RH cab console must
be set to the engine RUN position.
When the starter switch (C097) is turned to select engine
cranking, power is supplied to the engine stop switch via
pin 4 of the starter switch. With the engine stop switch in
the run position power is connected from pin 4 to the
MECU connector J2 pin 20 (C016).
The MECU responds with an output at connector J2 pin 7
which energises the engine crank relay R1 located on the
cab fuse and relay PCB. The relay contacts close and
starter relay (4) C262 energises. The relay contacts close
and the starter motor relay 009 energises which in turn
operates the starter motor. At the same time the input at
the engine ECU C251 pin 40 goes high and the engine
ECU energises the main relay (1) C321A. This enables
power supply to the engine ECU and engine devices as
follows:
K Fig 8. ( T C-71)
Item Device
- Variable Geometry
Turbocharger (VGT)
controller (1)
3 Relay - glow plugs
2 Relay - starter cut
5 Mass Air Flow (MAF) sensor
supply resistor
- Switch - Diesel Particle
Diffuser (DPD) regeneration
(1) Refer to the applicable engine documentation.
(2) Refer to Harness
Interconnections, in this section.
(3) Refer to Section 2.
The engine ECU can disable the starter motor circuit in
some circumstances, for example when the engine is
C-70

Engine Cranking

Connector
IC21 pin 3 (2)
C260 pin X1-2
C321B pin 5
C253 pin 1
C255 pin 2
(3)
Systems, Harness
9813/5100-1
Section C - Electrics
Engine and Power Control
running. When the low side input at C251 pin 92 turns ON
the starter cut relay (2) C321B energises. The contacts
open and the starter relay C262 de-energises. The starter
motor relay de-energises and the starter motor stops.
Engine Cranking
C-70