Malfunction indicator Lamp (MIL)

As a functional test, the MIL (check engine) illuminates at key-on before engine cranking. Whenever the Powertrain Control Module (PCM) sets a Diagnostic Trouble Code (DTC) that affects vehicle emissions, it illuminates the MIL. If a problem is detected, the PCM sends a message to the instrument cluster to illuminate the lamp. The PCM illuminates the MIL only for DTC's that affect vehicle emissions. There are some monitors that may take two consecutive trips, with a detected fault, before the MIL is illuminated, The MIL stays on continuously when the PCM has entered a Limp-In mode or identified a failed emission component. Refer to the Diagnostic Trouble Code charts in this group for emission related codes.

Also, the MIL either flashes or illuminates continuously whe the PCM detects active engine misfire. Refer to Misfire Monitoring in this section.

Additionally, the PCM may reste (turn off) the MIL when one of the following occur:

- PCM does not detect the malfunction for 3 consecutive trips (except misfire and Fuel system Monitors).
- PCM does not detect a malfunction while performing three successive engine misfire or fuel system tests, The PCM performs these tests while the engine is operating within + / - 375 RPM of and within 10% of the load of the operating condition at which the malfunction was first detected.

State Display Test Mode

The switch inputs to the Powertrain Control Module (PCM) have two recognized states; HIGH and LOW. For this reason, the PCM cannot recognize the difference between a selected switch position versus an open circuit, a short circuit, or a defective switch. If the State Display screen shows the change from HIGH to LOW or LOW to HIGH, assume the entire switch circuit to the PCM functions properly. Connect the DRB scan tool to the data link connector and access the state display screen. Then access either State Display Inputs and Outputs or State Display Sensors.

Circuit Actuation Test Mode

The Circuit Actuation Test Mode checks for proper operation of output curcuits or devices the Powertrain Control Module (PCM) may not internally recognize. The PCM attempts to activate these outputs and allow an observer to verify proper operation. Most of the tests provide an audible or visual indication of device operation (click of relay contacts, fuel spray, etc.). Except for intermittent conditions, if a device functions properly during testing, assume the device, its associated wiring, and driver circuit work correctly. Connect the DRB scan tool to the data link connector and access the Actuators screen.

Diagnostic Trouble Codes

A Diagnostic Trouble Code (DTC) indicates the PCM has recognized an abnormal condition in the system.

Diagnostic trouble codes are the results of a system or circuit failure, but de not derectly identify the failed component or components.

Technicians must retrieve stored DTC's by connecting the DRB scan tool (or an equivalent scan tool) to the 16-way data link connector (Fig.1)

Note: For a list of DTC's, refer to the charts in this section.

Diagnostic Trouble Codes

Warning : Apply Parking brake and/or block wheels before performing any test on an operating engine.
(1) Connect the DRB scan tool to data link (diagnostic) connector.
(2) Turn the ignition switch on, access Read Fault Screen. Record all the DTC's shown on the DRB scan tool.
(3) To erase DTC's, use the Erase Trouble Code data screen on the DRB scan tool.