Isuzu 4HL1, Workshop Manual

Page: 222 / 267

1A-220 Engine Control System
When Tech 2 has been connected to the vehicle, the
DTC can be cleared through the memory clear
operation with Tech 2.
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 at ECM: Inspect harness
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
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).
6. If pins are jumpered and the resistance reads
∞ Ω
,
the cause is open wiring. If pins are not jumpered and
the resistance reads 0
Ω
, the cause is short.
Step Action Value(s) Yes No
1
Perform the "On-Board Diagnostic (OBD)
System Check".
Was the OBD System Check performed?
—
Go to Step 2
Refer to OBD
System Check
and go to Step 2
2
Check the injector connector for installation
and, if mounted improperly, connect it
certainly.
Is the action complete?
—
Go to Step 3 —
3
Review the DTC.
1. Using Tech 2, check and store the DTC.
2. Clear the DTC.
3. Perform test run and review the DTC.
Is DTC271 detected?
—
Go to Step 4
Refer to
Diagnostic Aids
4
Check the cylinder 1 injector drive circuit for
+B short.
1. Starter switch "OFF".
2. Disconnect the ECM.
3. At the ECM connector pins, measure the
resistance.
Was the resistance within range?
Pins 43-109/
114/115/116:
∞ Ω
Go to Step 6 Go to Step 5
5
Repair or replace the faulty harness.
Is the action complete?
—
Verify repair and
go to Step 14 —
6
Check the cylinder 1 injector drive circuit
(ECM to intermediate connector) for open
wiring or short.
1. Disconnect the ECM.
2. Disconnect the injector connector.
3. Jumper the injector connector and
measure the resistance at the ECM
connector.
Was the resistance within range?
Pins 43-1
(jumpered:
pins 5-1): 0
Ω
(not jumpered):
∞ Ω
Go to Step 7 Go to Step 10