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/physical check of the Powertrain Control Module (PCM) and 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 and is displayed as CHECK ENGINE lamp.
MIL Function
| • | The MIL informs the driver that a malfunction has occurred and the vehicle should be taken in for service as soon as possible |
| • | The MIL illuminates during a bulb test and a system test |
| • | A DTC will be stored if a MIL is requested by the diagnostic |
MIL Illumination
| • | The MIL will illuminate with ignition switch ON and the engine not running |
| • | The MIL will turn OFF when the engine is started |
| • | The MIL will remain ON if the self-diagnostic system has detected a malfunction |
| • | The MIL may turn OFF if the malfunction is not present |
| • | If the MIL is illuminated and then the engine stalls, the MIL will remain illuminated so 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, then ON. |
Powertrain On Board Diagnostic (OBD) System Check
Perform the Powertrain On Board Diagnostic (OBD) System Check, when the following conditions are present:
| • | When the MIL does not turn ON when the ignition switch is turned to the RUN position. See above for MIL Operation |
| • | When the MIL remains ON while the engine is running |
| • | When the MIL is flashing while the engine is running |
| • | When a driveability symptom is determined |
Diagnostic Aids
Inspect for the following conditions:
Many situations may lead to an intermittent condition. Perform each inspection or test as directed.
Important: : Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.
| • | Loose terminal connection |
| - | Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair. |
| - | Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair. |
| • | Damaged harness--Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair. |
| • | Inspect the powertrain control module (PCM) and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair. |
If the condition is determined to be intermittent, reviewing the Snapshot or Freeze Frame/Failure Records may be useful in determining when the DTC or condition was identified.
Test Description
The numbers below refer to the step numbers on the diagnostic table:
-
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.
-
This test ensures that the PCM is capable of transmitting Class II serial data to the data link connector (DLC) and that the Class II 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 diagnostic table should be used to diagnose the condition.
-
If the engine will not start, the Engine Cranks But Will Not Run table should be used to diagnose the condition.
-
The scan tool may display DTCs which are diagnosed in 4T65-E Automatic Transaxle Diagnosis. Refer to 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:
-
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 e.g. switches, sensor range/performance, sensor high voltage, sensor low voltage, ODMs, etc. |
| • | System level DTCs e.g. Fuel trim, Misfire, EGR flow, TWC System, Idle Control System, HO2S Response or HO2S Transition Time Ratio. |
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
Important: :
Is the MIL illuminated? | -- | |||||||||||
Does the scan tool display PCM data? | -- | |||||||||||
3 | Attempt to start the engine Did the engine crank? | -- | ||||||||||
Did the engine start and continue to run? | -- | |||||||||||
|
Important: : If the scan tool indicates any DTCs set, record Freeze Frame and Failure Records. Use the scan tool in order to display diagnostic trouble codes (DTCs). Does the scan tool indicate any DTCs set? | -- | Go to applicable DTC | ||||||||||
With a scan tool, compare the PCM data to the Scan Tool Data List . Does the scan tool indicate PCM values equal to or within the typical values? | -- | System OK | Go to Component System Checks |
