On-Board Diagnostic (OBD) System Check: Notes

NOTE: Use of Tech 1 scan tool is required to perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK .

The OBD System Check determines:

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

After performing procedures in PRELIMINARY INSPECTION & ADJUSTMENTS and BASIC FUEL 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 OBD system 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.

Turn ignition on with engine off. Observe MALFUNCTION INDICATOR LIGHT (MIL) . If MIL illuminates, go to next step. If MIL does not illuminate, go to MALFUNCTION INDICATOR LIGHT (MIL) .
Turn ignition off. Install Tech 1 scan tool and follow scan tool manufacturer's instructions to proceed with test. Turn ignition on. If scan tool displays PCM data, go to next step. If scan tool does not display PCM data, go to DLC DIAGNOSIS OR NO SCAN TOOL DATA .
Using scan tool, command MIL to turn off. If MIL turns off, go to next step. If MIL does not turn off, diagnose using DTC P1641. See the TESTS W/CODES article.
Using scan tool, check if any DTC(s) are present. If DTC(s) are present, go to next step. If DTC(s) are not present, go to step 6).
Using scan tool, store FREEZE FRAME and FAILURE RECORDS data. Diagnose any stored DTC using the TESTS W/CODES article.
Start engine. If engine starts and runs, go to next step. If engine does not start, or starts and stalls/dies, go to NO-START DIAGNOSIS .
Turn ignition on with engine off. Check Engine Coolant Temperature (ECT). Start and warm engine to 194-203°F (90-95°C). Using scan tool, read ECT sensor value while engine reaches specified temperature. Compare scan tool value with actual control system values. If value is within limits, go to the TESTS W/O CODES article. If value is not within limits, diagnose DTC(s) using the TESTS W/CODES article.