Circuit Description
The Powertrain 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 PCM and engine grounds for being clean and tight. The Powertrain 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 (CHECK ENGINE) or (SERVICE ENGINE SOON). The MIL performs the following functions:
| • | It informs the driver that a problem has occurred and that the vehicle should be taken for service as soon as possible. |
| • | As a bulb check and 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, 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. |
Perform the Powertrain OBD System Check first, when the following conditions are present:
| • | When the MIL does not turn on when the ignition switch is turned to the RUN position. |
| • | When the MIL remains on while the engine is running. |
| • | When you suspect a driveability problem. |
Diagnostic Aids
Inspect all related wiring and connections including the connections at the PCM. These may cause an intermittent malfunction. Check terminals for the following:
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.
| • | Poor terminal connection. |
| Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Use a corresponding mating terminal to test for proper tension. Refer to Intermittents and Poor Connections Diagnosis , and Connector Repairs Wiring Systems. |
| • | Damaged harness. |
| Inspect the wiring harness for damage. If the harness appears to be OK, observe the sensor display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the sensor display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems. |
| • | Inspect the PCM and the engine grounds for clean and secure connections. |
If the DTC is determined to be intermittent, reviewing the Fail Records can be useful in determining when the DTC was last set.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 |
Is the MIL on? | -- | ||
2 |
Does the scan tool display PCM data? | -- | ||
3 | Attempt to start the engine. Did the engine start and continue to run? | -- | ||
4 | Display DTC Info Last Tst Fail. If any DTCs are stored as last test failed, save the freeze frame and fail record information using the Capture Info feature on the scan tool. Are any DTCs indicated as last test failed? | -- | Diagnose the applicable DTCs | |
5 | Display DTC Fail Records with the scan tool. If any DTC Fail Records are stored, save the freeze frame and fail record information using the Capture Info feature on the scan tool. Are any Fail Records stored? | -- | Go to applicable DTC table | |
6 | Compare PCM data values displayed on the scan tool to the typical engine scan data values. Are the displayed values normal or close to the typical values? | -- | System OK | Go to indicated Component System Checks |
