On-Board Diagnostic (OBD) System Check: Notes

NOTE: Tech 1 scan tool is required to perform OBD system check.

The OBD System Check determines:

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

After performing procedures in PRELIMINARY INSPECTION & ADJUSTMENTS, BASIC FUEL SYSTEM CHECKS and BASIC IGNITION SYSTEM CHECKS, this is the starting point for utilizing the self-diagnostic system for determining computer-related problems. After performing necessary tests as described in the diagnostic circuit check, if no codes are indicated and driveability problems still exist, see the TESTS W/O CODES article and SCAN TOOL USAGE in the TESTS W/CODES article.

Connect scan tool to Data Link Connector (DLC). Turn ignition on with engine off. If scan tool does not display data, go to next step. If scan tool displays data, go to step 3).
Using scan tool, select DIAGNOSTIC CIRCUIT CHECK, CLASS 2 MESSAGE MONITOR. If scan tool displays other modules as active, go to DLC DIAGNOSIS OR NO SCAN TOOL DATA . For any modules not displayed as active by scan tool, go to appropriate system article in the ACCESSORIES/SAFETY EQUIPMENT section for diagnosis of faulty module.
If engine starts and continues to run, go to next step. If engine does not start or continue to run, go to NO START - ENGINE CRANKS OKAY under NO START DIAGNOSIS .
If engine continues to run after vehicle exceeds 2 MPH, go to next step. If engine does not continue to run after vehicle exceeds 2 MPH, go to the BODY CONTROL MODULE article in the ACCESSORIES/SAFETY EQUIPMENT section.
Using scan tool, check if DTC P1626 or DTC P1631 stored in history. If either DTC is stored, diagnose DTC. See the TESTS W/CODES article. If neither DTC is stored, go to next step.
Using scan tool, observe DTC information. If DTC status LAST TEST FAILED, TEST FAILED THIS IGNITION, MIL REQUEST, or HISTORY DTCs are set, save DTC FREEZE FRAME and/or FAILURE RECORDS information, or REFRESH INFO. If any DTCs are displayed, diagnose DTC. See the TESTS W/CODES article. If no DTCs are displayed, go to next step.
Compare scan tool engine data with actual control system data values. If value is within limits, see the TESTS W/O CODES article. If value is not within limits, go to next step.
Vehicle is equipped with a column lock system. System is necessary because of location of ignition lock cylinder. Body Control Module (BCM) controls a motor mounted on steering column that unlocks steering wheel. If BCM is unable to determine if column is unlocked or if vehicle speed is present, Powertrain Control Module (PCM) will disable fuel.
If condition is intermittent, check for improper installation of electrical components. Inspect aftermarket theft deterrent devices, lights and cellular telephones. Ensure aftermarket equipment is not connected to Class 2 circuit. If intermittent condition cannot be located, cellular telephone communication signal may be cause.

If multiple DTCs are set, check IGN 1 mini relay operation. Relay protects battery from parasitic draw and powers transmission, EVAP solenoid, MAF sensor, AIR pump and AIR solenoid relays, and TCC/Cruise and extended-travel brake switches.