Why is check engine light on 1997 Kia Sportage have changed oil and checked everything no smoke noise runs fine?

Even if your 1997 Kia Sportage runs fine, a check engine light can illuminate for a variety of reasons beyond obvious mechanical issues. Since you've changed the oil and done a visual inspection, the problem is likely something the engine's computer detected that isn't immediately apparent.

Here are the most common reasons:

* Faulty Oxygen Sensor (O2 Sensor): This is a very common cause of a check engine light. The O2 sensor monitors the exhaust gases to regulate the air/fuel mixture. A faulty sensor can lead to poor fuel economy and emissions issues, even if the engine runs smoothly.

* Mass Airflow Sensor (MAF Sensor): This sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor can cause incorrect air/fuel mixtures, leading to the check engine light.

* Catalytic Converter Issues: A failing catalytic converter can trigger the check engine light. While you might not notice a performance issue immediately, the computer detects the problem.

* Evaporative Emission System (EVAP) Leak: This system prevents fuel vapors from escaping into the atmosphere. A leak in the system can trigger the light, even if the engine operates normally.

* Other Sensors: Various other sensors (e.g., crankshaft position sensor, camshaft position sensor) can fail and trigger the light.

* Loose Gas Cap: Believe it or not, a loose or damaged gas cap can cause a small vacuum leak in the EVAP system and trigger the check engine light. Try tightening it first.

What you need to do:

1. Get the Diagnostic Trouble Codes (DTCs) read: This is the most crucial step. You'll need a code reader (OBD-II scanner) to read the DTCs stored in your vehicle's computer. Auto parts stores often offer this service for free. The codes will provide a clue about the specific problem.

2. Interpret the Codes: Once you have the codes, look them up online (many websites provide DTC definitions). This will help pinpoint the likely cause.

3. Address the Issue: Based on the DTCs, you can decide whether to attempt a repair yourself (if you're mechanically inclined) or take it to a mechanic.

Ignoring the check engine light is not recommended. While your Sportage may run fine now, the underlying problem could worsen and cause more significant (and expensive) damage down the road. Getting the codes read is the first, and most important, step to resolving the issue.