Isuzu 4HL1 Workshop Manual page 119

Diagnostic Aids
Poor connection or damaged harness may cause
intermittents. Check for the following conditions and, if
the fault is detected, repair or replace the faulty portion.
• Poor connection
connectors for backed-out pins, improper mating,
broken locks, improperly formed or damaged pins,
and poor pin-to-wire connection.
• Damaged harness: Inspect the wiring harness for
rubbed-through wire insulation or wire broken
inside the insulator. If the harness appears to be
Step
Perform the "On-Board Diagnostic (OBD)
System Check".
1
Was the OBD System Check performed?
Check the VS sensor connector for installation
and, if mounted improperly, install the device
2
certainly.
Is the action complete?
Review the DTC.
1. Using Tech 2, check and store the DTC.
2. Clear the DTC.
3
3. Perform test run and review the DTC.
Is DTC25 detected?
Check the speedometer for operation.
1. Run the vehicle.
4
2. Check the speedometer.
Is the speedometer working correctly?
Check the VS sensor signal circuit for open
wiring.
1. Starter switch "OFF".
2. Jumper the VS sensor connector and
5
measure the resistance at the VIM
connector.
Was the resistance within range?
Check the VS sensor power circuit for open
wiring.
1. Starter switch "OFF".
2. Disconnect
connectors.
6
3. Starter switch "ON".
4. At the VS sensor connector power pins,
measure the voltage.
Was the voltage within range?
at VIM: Inspect harness
Action
VIM and VS
OK, observe the display on Tech 2 while moving
connectors and wiring harnesses related to the
sensor. A change in the display will indicate the
location of the fault.
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart.
3. If the DTC is not detected, the possible cause is
intermittent (intermittent fault).
Value(s)
—
—
—
—
Pins 14-
ground
(jumpered:
pins 2-
ground): 0 Ω
sensor
Pins 1-
ground: 24 V
Engine Control System 1A-117
Yes
Go to Step 2 and go to Step 2
Go to Step 3
Go to Step 4 Diagnostic Aids
Go to Step 5
Go to Step 13
Go to Step 7
No
Refer to OBD
System Check
—
Refer to
Go to Step 6
Go to Step 9
Go to Step 9