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 System Function: Notes
The on board diagnostic system has the following three functions.
| Diagnostic Test Mode | KEY and ENG. Status | Function | Explanation of Function |
|---|---|---|---|
| Mode I | Ignition switch in ON position | BULB CHECK | This function checks the MIL bulb for damage (blown, Engine stopped open circuit, etc.). If the MIL does not come on, check MIL circuit. |
| Engine running | MALFUNCTION WARNING | This is a usual driving condition. When a malfunction is detected twice in two consecutive driving cycles (two trip detection logic), the MIL will light up to inform the driver that a malfunction has been detected. The following malfunctions will light up or blink the MIL in the 1st trip.
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| Mode II | Ignition switch in ON position | SELF-DIAGNOSTIC RESULTS | This function allows DTCs and 1st trip DTCs to be read. |
When there is an open circuit on MIL circuit, the ECM cannot warn the driver by lighting up MIL when there is malfunction on engine control system.
Therefore, when electrical controlled throttle and part of ECM related diagnoses are continuously detected as NG for 5 trips, ECM warns the driver that engine control system malfunctions and MIL circuit is open by means of operating fail-safe function.
The fail-safe function also operates when above diagnoses except MIL circuit are detected and demands the driver to repair the malfunction.
| Engine operating condition in fail-safe mode | Engine speed will not rise more than 2, 500 RPM due to the fuel cut |
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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.