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.
The OBD System Check Determines
- If Malfunction Indicator Light (MIL) works.
- If PCM is operating and can recognize a fault.
- If any codes 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 TESTS W/O CODES article and SCAN TESTER USAGE in 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 ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK .
- 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 A-2/A-4, DLC DIAGNOSIS OR NO SCAN TOOL DATA.
- Attempt to start engine. If engine start and runs, go to next step. If engine does not start or starts and dies, go to NO START DIAGNOSIS (A-3) .
- Using scan tool, select DTC, DTC INFO and LAST TST FAIL function. If any DTC is stored, go to next step.
- Using scan tool, save freeze frame and fail record information using CAPTURE INFO feature. If any DTC is indicated as last test failed, diagnose DTC using TESTS W/CODES article. If DTC is not stored, check related circuit or component(s). See SYSTEM/COMPONENT TESTS article.
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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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.
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