Isuzu 4ja1, Workshop Manual

Page: 491 / 564

Engine Control System (4JH1) 6E-237
Symptoms – Engine Controls
Symptoms – Engine Controls
Important Preliminary Inspections Before Starting
Perform Diagnostic System Check – Engine Controls
before using the symptom tables, and verify that all of
the following are true:
•
The engine control module (ECM) and malfunction
indicator lamp (MIL) are operating correctly.
•
There are no diagnostic trouble codes (DTCs)
stored, or a DTC exists but without the MIL.
•
The scan tool data is within the normal operating
range. Refer to scan tool Data List in this section.
•
Verify the customer concern and locate the correct
symptom in the table of contents. Inspect the items
indicated under that symptom.
Visual and Physical Inspection
Several of the symptom procedures ask for careful
visual and physical inspection. This step is extremely
important. The visual and physical inspection can lead
to correcting a problem without further inspections, and
can save valuable time. Ensure that:
•
The ECM grounds are clean, tight, and in their
proper location.
•
The vacuum hoses are not split or kinked, and
properly connected. Inspect thoroughly for any
type of leak or restriction.
•
The mass air flow (MAF) sensor is properly
installed. The arrows on the plastic portion of the
sensor must point toward the engine.
•
The air intake ducts are not collapsed or damaged.
•
There are no leaks at the MAF sensor, any
connections or intake manifold sealing surfaces.
•
The engine harness wiring and terminals are
properly connected and are not pinched or cut.
Intermittent
Important:
Inspect for improper installation of electrical
components if an intermittent condition exists. Inspect
for aftermarket add-on electrical equipment devices,
lights, and cellular phones. Verify that no aftermarket
equipment is connected to the keyword 2000 serial data
circuit. If you cannot locate an intermittent condition, a
cellular phone communication signal may cause the
condition.
Important:
The problem may or may not turn ON the MIL or store a
DTC.
Faulty electrical connections or wiring cause most
intermittent problems. Perform a careful visual and
physical inspection of the suspect connectors for the
following conditions:
•
Improperly mated connector halves
•
Terminals that are not seated
•
Terminals that are damaged or improperly formed
Reform or replace connector terminals in the problem
circuit in order to ensure proper contact tension.
Remove the terminal from the connector body in order
to inspect for poor terminal wire connection.
Road test the vehicle with the DMM connected to the
suspected circuit. An abnormal reading that occurs
when the malfunction occurs is a good indication that
there is a malfunction in the circuit being monitored.
Use the scan tool in order to help detect intermittent
conditions. Useful features of the scan tool include the
following:
•
Trigger the Snapshot feature in order to capture
and store engine parameters when the malfunction
occurs. Review this stored information in order to
see the specific running conditions that caused the
malfunction.
•
Use the Plot Function on the scan tool in order to
plot selected data parameters. Review this stored
information to aid in locating an intermittent
problem. Refer to the scan tool Users Guide for
more information.
Important:
If the intermittent condition exists as a start and then
stall, test for DTCs relating to the vehicle theft deterrent
system. Test for improper installation of electrical
options such as lights, cellular phones, etc.
Any of the following may cause an intermittent MIL with
no stored DTC:
•
The ECM grounds are loose or dirty. Refer to
Engine Controls Schematics.
•
The MIL circuit intermittently shorted to ground.
•
Electrical system interference caused by a
malfunctioning relay, ECM driven solenoid, or
switch. The electrical component can cause a
sharp electrical surge. Normally, the problem will
occur when the malfunctioning component is
operating.
•
There is an open diode across the A/C
compressor clutch or any other open diodes.