4. Troubleshooting
4-15
4.5
Explanation of Trouble Diagnosis
No. Item
Cause
Remedy
A Faulty
unloader.
Unloader valve cannot be open.
Remove unloader assembly
from compressor air-end, and
disassemble it for inspection
and replace O-ring.
B Check pressure sensor
output voltage.
Engine speed is controlled by the proper
speed finally outputted to electro-control
fuel injection system in the following
flows after pressure sensor detects
second stage pressure of regulator.
Therefore, when abnormality is found in
rotational speed, it is necessary that
pressure sensor, emergency controller,
engine controller (ECU) and related
wires should be checked and confirmed
whether they are disconnected and/or
short-circuited.
3.2 clause: Emergency
Controller
3.12 clause: Check output
voltage referring to
“Pressure Sensor”
C Check
emergency
controller output
voltage.
D Check if engine
controller (ECU)
functions well.
Check and confirm in
accordance with the “4.6
Engine Trouble Diagnosis
Function”.
E Check and confirm that
safety valve functions at
lower pressure than set
pressure.
Check and locate pressure
maladjustment or defective safety valve.
In case of malfunction of
safety valve, safety valve
should be replaced.
F Faulty
unloader.
Faulty seat of unloader valve or faulty
function of unloader piston.
Remove unloader assembly
from compressor air-end, and
disassemble it for inspection
and replace O-ring.
G Check discharge air
temperature.
Check whether actual rise of discharge
air temperature stops engine or any
failure of electrical circuit stops engine.
H Check resistance of
discharge temperature
sensor.
For temperature and resistance
characteristics of discharge temperature
sensor, see 3.11.
Even disconnection of sensor
or its short-circuit causes
engine to stop.
I Check of electric
conductance between
emergency controller
CN2-9 terminal and
discharge temperature
sensor.
In case that no electrical conductance
exists, engine will stop with controller
disconnection detecting function 20
seconds after engine starts. In case of
short-circuit, engine will be brought to
emergency stop.
Repair disconnection and
short-circuit.
Pressure sensor
Output voltage
Emergency controller
Output voltage
Engine controller (ECU)
(Control signal)
Electronic control fuel
injection system
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