Inspections
| Action
|
Definition: The condition is not currently
present but is indicated in DTC History.
OR
There is a customer concern, but the symptom can not currently be duplicated
(if the condition is not DTC related).
|
Visual/Physical Inspection
| This
step is an important aid for locating a condition without extensive testing.
Perform a visual/physical inspection of the following items:
| • | Wiring harness for damage or cuts. |
| • | A misrouted harness that is too close to high voltage/high current
devices such as secondary ignition components, motors and generators. These
components may induce electrical noise on a circuit that could interfere
with normal circuit operation. |
| • | Vacuum hoses for proper routing, connections, splits or kinks. |
| • | Verify the Mass Air Flow (MAF) sensor is installed correctly.
The arrows on the housing should point toward the engine. |
| • | Air leaks at the throttle body mounting area, MAF, and the intake
manifold sealing surfaces. |
| • | PCM and body grounds for being clean and tight. |
| • | Battery connections are clean and tight. |
|
Harness/Connector Inspection
|
| • | Many intermittent conditions occur with harness/connector movement
caused by vibration, engine torque, rough pavement or component operation.
Refer to
Testing for Electrical Intermittents
in Wiring Systems. |
| • | Excessive circuit resistance can cause a component to be inoperative.
If the suspect component does not respond to scan tool commands, then inspect
all related circuits for excessive resistance. Refer to
Testing for Continuity
in Wiring Systems. |
|
Duplicating Failure Conditions
| Freeze Frame/Failure Records data (where applicable)
can be used to duplicate the conditions under which a DTC sets.
- Review and record Freeze Frame/Failure Records data
- Clear DTCs using the scan tool.
- Turn Off the ignition for 30 seconds.
- Operate the engine as close to the conditions that were noted
in Freeze Frame/Failure Records. The engine must also be operating within
the conditions for running the DTC, refer to Conditions for Running
the DTC.
- Monitor the DTC Status for the DTC being tested. The scan tool
will indicate Ran, when the enabling conditions have been met. The scan tool
will also indicate whether the DTC passed or failed.
| • | The J 42598
Vehicle Data recorder allows the customer, or the technician, to drive the
vehicle and capture data as the intermittent condition occurs. Pressing
a button on the Vehicle Data Recorder, while the intermittent condition
is present, records PCM data which can be used to isolate the condition. |
| • | An alternate method is to drive the vehicle with the DMM J 39200
connected to the suspected
circuit. An abnormal reading on the DMM when the condition occurs, may help
you locate the condition. |
| • | Compare the Freeze Frame/Failure Records with the typical values
in the Scan Tool Data List. |
|
Scan Tool Snapshot
| The scan tool can be set up to take a 'snapshot' of the parameters available
via serial data. The Snapshot function records live data over a period
of time. The recorded data can be played back and analyzed. The scan
tool can also graph parameters individually or in combinations of parameters
for comparison. The snapshot can be triggered manually at the time
the symptom is noticed, or set up in advance to trigger when a DTC sets.
An abnormal value captured in the recorded data may point to a system
or component that needs further investigation.
Refer to the scan tool user instructions for more information on the
Snapshot function.
|
Intermittent Malfunction Indicator Lamp (MIL)
with NO DTCs
| The following conditions may cause an intermittent MIL and no DTCs:
| • | Electrical system interference caused by a malfunctioning relay,
PCM controlled solenoid or switch. |
| • | Improper installation of non-factory (aftermarket) add on accessories
such as cellular phones, alarms, lights, or radio equipment. |
| • | The Malfunction Indicator Lamp (MIL) circuit intermittently shorted
to ground. |
|
Additional Inspections
| Test for an open diode across the A/C compressor clutch and for other open
diodes.
Inspect for improper installation of non-factory (aftermarket) add on
accessories such as cellular phones, alarms, lights, or radio equipment.
Excessive circuit resistance can cause a component to be inoperative.
If the suspect component does not respond to scan tool commands, then inspect
all related circuits for excessive resistance. Refer to
Testing for Continuity
in Wiring Systems.
Test the generator for a bad rectifier bridge that may induce AC electrical
noise to the electrical system. Refer to
Diagnostic Starting Point - Engine Electrical
in Engine Electrical.
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