Isuzu 4HL1 Workshop Manual page 256

1A-254 Engine Control System
3 Refrigerator switch (N/C)
QWS switch (N/O)
A/C switch (N/O)
PTO switch (N/O)
4 Starter cut relay (N/C)
5 Starter relay (N/O)
Main relay (N/O)
6 A/C relay (N/O)
7 Glow relay (N/O)
1 System voltage / battery
2 SCV
3 Injector
4 Intake throttle system
5 EGR system
6 Exhaust brake
7 Atmospheric pressure sensor
8 Idle up volume
1. Move the starter switch to the "OFF" position and observe
the display for each switch.
2. When any of the switches is not turned off, check the switch
circuit and the single switch for short.
1. Check the relay and relay circuit for short.
1. Check the relay and relay circuit for open wiring.
1. Check the relay and relay circuit for short.
1. Check the "Glow Time Relay" display appears within 18
seconds after turn-on of starter switch.
2. When the glow relay is not turned on, continuity-test the
glow relay system circuit (coil side) and glow relay.
C: Others
1. Observe the "System Voltage" display.
Reference value: 19-32 V
(In case of no cranking, directly measure the battery voltage
with tester instead of Tech 2.)
1. Start the engine and change the engine speed to observe
"SCV Duty Ratio" and "SCV Current" displays.
"SCV Duty Ratio" is decreased when the engine speed is
added.
"SCV Current" is decreased when the engine speed is
reduced.
1. Perform the injector balance test to check all the injectors
are working.
2. Observe the "Cylinder (1-4) Compensation" display for
individual cylinders to check all the cylinders acquire equal
calibrated fuel quantity.
3. If faulty cylinder(s) are identified, clean or replace it (them).
1. Perform the intake throttle test to check the "Actual Intake
Throttle Position" follows the "Desired Intake Air Throttle
Position".
2. If the actual value does not follow the desired value, check
the intake throttle valve for sticking and the motor for fault.
1. Perform the EGR control test to check the "EGR Current
Position" follows the "EGR Target Lift Position".
2. If the actual value does not follow the desired value, check
the EGR valve for sticking and the motor for fault.
1. Operate the exhaust brake to check the "Exhaust Brake
Switch" display changes between "On" and "Off".
2. If the display does not follow the operation, check the
exhaust brake valve for sticking and the solenoid valve for
fault.
1. Observe the "Barometric Pressure" display for abnormal
value.
1. Set the idle up volume to the minimum and observe the "Idle
Up Volume" display.
Reference value: 0.55 V
2. Check the voltage for excessively high value or variation.