GM Service Manual Online
For 1990-2009 cars only

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:

    â€¢ Wiring harness for damage or cuts.
    â€¢ 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.
    â€¢ Vacuum hoses for proper routing, connections, splits or kinks.
    â€¢ Verify the Mass Air Flow (MAF) sensor is installed correctly. The arrows on the housing should point toward the engine.
    â€¢ Air leaks at the throttle body mounting area, MAF, and the intake manifold sealing surfaces.
    â€¢ PCM and body grounds for being clean and tight.
    â€¢ Battery connections are clean and tight.
    â€¢ Charging System for proper operation. Refer to Diagnostic Starting Point - Engine Electrical in Engine Electrical.

Harness/Connector Inspection

    â€¢ 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.
    â€¢ 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.

  1. Review and record Freeze Frame/Failure Records data
  2. Clear DTCs using the scan tool.
  3. Turn Off the ignition for 30 seconds.
  4. 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.
  5. 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.
    â€¢ 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.
    â€¢ 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.
    â€¢ 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:

    â€¢ Electrical system interference caused by a malfunctioning relay, PCM controlled solenoid or switch.
    â€¢ Improper installation of non-factory (aftermarket) add on accessories such as cellular phones, alarms, lights, or radio equipment.
    â€¢ The Malfunction Indicator Lamp (MIL) circuit intermittently shorted to ground.
    â€¢ Poor PCM grounds.

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.