On-Board Diagnostic (OBD) System Check

NOTE: Check for applicable Technical Service Bulletins (TSBs) before proceeding. DO NOT perform the following procedure if driveability conditions are not present. DO NOT turn ignition off during the following procedure or clear DTCs unless instructed to do so.

NOTE: Use of scan tool is required to perform OBD system check. Perform this test prior to performing any diagnostic procedures in diagnostic tests. For scan tool data values, refer to scan tool manufacturer's instruction manual.

NOTE: Most problems that exist with the MIL or diagnostic system are engine performance or PCM related. Procedures for repairing these systems and circuits may need additional engine performance repair data. This test contains references to additional procedures not found in this publication.

The OBD system check determines:

If Malfunction Indicator Light (MIL) works.
If PCM is operating and can recognize a fault.
If any DTCs are stored.

OBD system check is the starting point for utilizing the self-diagnostic system for determining computer-related problems. After performing necessary tests as described in OBD system check, if no DTCs are indicated and driveability problems still exist, see appropriate TROUBLE SHOOTING - NO CODES article in ENGINE PERFORMANCE.

NOTE: The following steps should be performed first to reduce diagnostic time and prevent replacement of good parts.

Connect scan tool to 16-pin Data Link Connector (DLC), located under left side of instrument panel. Turn ignition switch to ON position. If scan tool powers up, go to next step. If scan tool does not power up, see NO DATA LINK CONNECTOR DATA under SYMPTOM TESTS.
Observe MIL. If MIL is illuminated, go to next step. If MIL is not illuminated, see NO MALFUNCTION INDICATOR LIGHT under SYMPTOM TESTS.
Using scan tool, attempt to communicate with PCM. If scan tool communicates with PCM, go to next step. If scan tool does not communicate with PCM, see NO DATA LINK CONNECTOR DATA under SYMPTOM TESTS.
Using scan tool, check for DTCs. Record freeze frame and failure records information. Identify DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . After identification, diagnose DTCs. See DIAGNOSTIC TESTS . If no DTCs are stored, see appropriate TROUBLE SHOOTING - NO CODES article in ENGINE PERFORMANCE.