Circuit Description
The Powertrain On-Board Diagnostic (OBD) System Check must be the starting point for any driveability complaint diagnosis. Before using this procedure, you should perform a careful visual and physical check of the powertrain control module (PCM) and the engine grounds for being clean and tight. The Powertrain On-Board Diagnostic (OBD) System Check is an organized approach to identifying a problem created by an electronic engine control system malfunction.
MIL Operation
The malfunction indicator lamp (MIL) is located on the instrument panel. The MIL performs the following functions:
| • | Informs the driver that a problem has occurred and that the vehicle should be serviced as soon as possible. |
| • | As a system check, the MIL will illuminate with the ignition switch ON and the engine not running. When the engine is started, the MIL will turn OFF. If the MIL remains ON, the self-diagnostic system has detected a problem. If the problem goes away, the MIL will turn OFF in most cases, but a diagnostic trouble code will remain stored. |
| • | If the MIL is illuminated and the engine stalls, the MIL will remain Illuminated as long as the ignition switch is ON. |
| • | If the MIL is not illuminated and the engine stalls, the MIL will not illuminate until the ignition switch is cycled OFF and then ON. |
Perform the Powertrain On-Board Diagnostic (OBD) System Check first when the following conditions are present:
| • | The MIL does not turn ON when the ignition switch is turned to the RUN position. |
| • | The MIL remains ON while the engine is running. |
| • | If you suspect a driveability problem. |
Diagnostic Aids
An intermittent may be caused by:
| • | A poor connection |
| • | A rubbed-through wire insulation |
| • | A wire broken inside the insulation |
Check for poor connections or a damaged harness.
Inspect the PCM harness and connectors for:
| • | Improper mating |
| • | Broken locks |
| • | Improperly formed or damaged terminals |
| • | Poor terminal-to-wire connections |
| • | A damaged harness |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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The MIL should be ON steady with the key ON and the engine OFF. If not, the No Malfunction Indicator Lamp table should be used to isolate the malfunction.
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Important: Make sure to use the 2001 3.0L LW9 option on the scan tool.
This test ensures that the PCM is capable of transmitting Class 2 serial data to the data link connector (DLC) and that the Class 2 data circuit is not open or shorted. If a problem is encountered and a malfunctioning scan tool is suspected, try the scan tool on another vehicle to verify operation. If a DLC problem exists, the DLC diagnosis table should be used to diagnose the condition.
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If the engine will not start, the Engine Cranks But Will Not Run table should be used to diagnose the condition.
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The scan tool may display diagnostic trouble codes (DTCs) which are diagnosed in 4T65-E Automatic Transaxle Diagnosis. Refer to the DTC List for a complete list of DTCs supported by this vehicle application. If multiple DTCs are stored, diagnose each DTC according the following priority:
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A scan tool parameter which is not within the typical range may help to isolate the area which is causing the problem.
| • | PCM error DTCs |
| • | System voltage DTCs |
| • | Component level DTCs |
| • | System level DTCs |
Step | Action | Values | Yes | No | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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Important:
Is the MIL illuminated? | -- | |||||||||||||
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Important: For the 3.0L LW9 use the scan tool menu option 2001 3.0 LW9.
Does the scan tool display the PCM data? | -- | |||||||||||||
3 | Attempt to start the engine. Does the engine crank? | -- | ||||||||||||
Does the engine start and continue to run? | -- | |||||||||||||
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Important: If the scan tool indicates any DTCs set, record the Freeze Frame and Failure Records. Use the scan tool in order to display the DTCs. Does the scan tool indicate any DTCs set? | -- | Go to the applicable DTC tables | ||||||||||||
With a scan tool, compare the PCM data to the Scan Tool Data List. Refer to Scan Tool Data List . Does the scan tool indicate PCM values equal or within the typical values? | -- | System OK | Go to the Component System Checks |
