Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
On-Board Diagnostic (OBD) System Check
The OBD system check determines:
- If Malfunction Indicator Light (MIL) operates.
- If ECM 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 in appropriate BASIC DIAGNOSTIC PROCEDURES article, 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 check, if no DTCs are indicated and driveability problems still exist, see appropriate TROUBLE SHOOTING - NO CODES article and SCAN TOOL USAGE .
- Connect scan tool to 16-pin DLC located under left side of instrument panel. See Fig 1. If scan tool does not power up, check power to DLC. See WIRING DIAGRAMS article. If scan tool powers up, go to next step.
- Check for stored DTCs. If DTC(s) are stored, go directly to affected DTC(s). If no DTC(s) are present, scan serial data stream transmitted by ECM. See scan tool manufacturer's instructions.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.