Symptoms - Engine Controls - Isuzu N 2008 Series Workshop Manual

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 ECM and malfunction indicator lamp (MIL)/
service vehicle soon (SVS) lamp are operating
correctly.
• 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 air intake ducts are not collapsed or damaged.
• The exhaust pipes are not collapsed or damaged.
• 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 controller area network
(CAN) or other serial data circuit.
Important: The problem may or may not turn ON the
MIL/ SVS lamp or store a DTC. Faulty electrical
connections or wiring
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
Symptoms - Engine Controls
cause most intermittent
Engine Control System (4JJ1)
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 Tech 2 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.
• Freeze Frame/ Failure Record can also aid in
locating an intermittent condition. Review and
capture the information in the Freeze Frame/
Failure Record associated with the intermittent
DTC being diagnosed. Drive the vehicle within the
conditions that were present when the DTC
originally set.
• 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 scan tool Users Guide for more
information.
Use the data recording module (DRM) or the body
control module (BCM) data recording function in order
to help detect intermittent conditions. The DRM or the
BCM has ability to store engine log data when an event
of DTC. Maximum three log data can be stored in the
DRM or the BCM memory. If more than maximum
number of storage is set, oldest log data is overwritten.
However, if same DTC is set within eight hours that
DTC is not stored in the DRM or the BCM memory.
The manual trigger function is to store the log data by
an arbitrary operation of the driver when an event of
wrong vehicle performance that is instead of an event
of DTC. If the driver presses and releases the manual
trigger switch once, that time becomes a trigger and
one log data before and behind the trigger is stored in
the DRM or the BCM memory. When there is a space in
the DRM or the BCM memory, log data is stored in that
space. However, when more than maximum number of
storage is set, oldest log data is overwritten.
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/
SVS lamp with no stored DTC:
• The ECM grounds are loose or dirty. Refer to
engine control wirings.
1A-321