Inspections
| Action
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DEFINITION: The condition is not currently present but is indicated in DTC History.
OR
There is a customer concern, but the symptom cannot currently be duplicated, if the condition is not DTC related.
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Visual/Physical Inspection
| This step is an important aid in locating a condition without extensive testing. Perform a visual/physical inspection of the following items:
| • | Inspect the wiring harness for damage. |
| • | Inspect for a mis-routed harness that is too close to high voltage or high current devices such as the following: |
| - | Motors and generators. These components may induce electrical noise on a circuit which can interfere with normal circuit operation. |
| - | Secondary ignition components. |
| • | Inspect the vacuum hoses for splits or kinks. Verify that the connections and routing are as shown on the Vehicle Emission Control Information label. |
| • | Inspect for air leaks at the throttle body mounting and intake manifold sealing surfaces. |
| • | Verify that the engine control module (ECM) grounds and the body grounds are clean, tight, and in the correct locations. |
| • | Verify that the battery connections are clean and tight. |
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Harness/Connector Inspection
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| • | 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 a component does not respond to a scan tool command, test the related circuits for excessive resistance. Refer to
Testing for Continuity
in Wiring Systems. |
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Duplicating Failure Conditions
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| • | 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 ECM data which can be used to isolate the condition. |
| • | An alternate diagnosis method is to drive the vehicle with a DMM connected to the suspected circuit. An abnormal reading on the DMM may indicate a failure condition. |
| • | 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 combination with other 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 requires further investigation. |
| | Refer to the scan tool user instructions for more information on the Snapshot function. |
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Intermittent malfunction indicator lamp (MIL) with NO DTCs
| The following conditions may cause an intermittent MIL and no DTCs:
| • | Electromagnetic Interference (EMI) caused by a malfunctioning relay, ECM controlled solenoid or switch. |
| • | The incorrect installation of non-factory or aftermarket add on accessories such as cellular phones, alarms, lights, or radio equipment. |
| • | The MIL control circuit is intermittently shorted to ground. |
| • | The ECM grounds are loose. |
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Additional Inspections
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| • | Test for excessive circuit resistance. If a component does not respond to a scan tool command, test the related circuits for excessive resistance. Refer to
Testing for Continuity
in Wiring Systems. |
| • | Test for an open diode across the A/C compressor clutch and for other open diodes. |
| • | Inspect for the following charging system conditions: |
| - | The generator for a bad rectifier bridge that may induce AC electrical noise in the electrical system. Refer to
Charging System Test
in Engine Electrical. |
| - | The generator for incorrect output voltage. Refer to
Symptoms - Engine Electrical
in Engine Electrical. Repair the charging system if the generator output voltage is less than 9 volts or more than 18 volts. |
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