{"name":"OBD2HQ Diagnostic First-Check Checklist","license":"Free to reference with attribution to OBD2HQ","sourceUrl":"https://obd2hq.com/en/resources","lastReviewed":"2026-07-14T12:00:00.000Z","checklist":[{"id":"safety-first","title":"Check safety first","items":["Stop driving if oil pressure, coolant temperature, brake warning or flashing check engine light is active.","Do not open a hot cooling system.","If braking feels weak or the pedal sinks, tow the vehicle instead of driving."]},{"id":"scan-and-freeze-frame","title":"Scan codes and save freeze-frame data","items":["Read stored, pending and permanent OBD2 codes.","Save freeze-frame speed, load, coolant temperature, fuel trim and RPM before clearing codes.","Record warning lights and symptoms in plain language."]},{"id":"visual-inspection","title":"Inspect simple causes before replacing parts","items":["Check battery voltage, fuses, grounds and obvious connector damage.","Inspect intake hoses, vacuum lines, fluid levels and leaks.","Look for recent repair work near the affected system."]},{"id":"live-data","title":"Compare live data","items":["Compare sensor values against realistic engine conditions.","Use fuel trims, oxygen sensor activity, MAF/MAP values and temperature readings to confirm direction.","Do not replace sensors until wiring, power, ground and signal behavior are checked."]},{"id":"verify-repair","title":"Verify the repair","items":["Clear codes only after a repair or confirmed correction.","Complete the required drive cycle.","Re-scan for pending codes and confirm the symptom did not return."]}]}