3 most common reasons your check engine light comes on
By: Luke Shaff & Team ~
11/13/2025
Here are the 3 most common reasons your check engine light comes on –
- Faulty Oxygen Sensor (O2 Sensor)
- What it does: Measures the amount of unburned oxygen in the exhaust.
- Why it matters: A bad sensor can lead to poor fuel economy and higher emissions.
- Check engine result: The engine control unit (ECU) detects incorrect readings and triggers the light.
- Loose, Damaged, or Missing Gas Cap
- What it does: Seals the fuel system and maintains pressure.
- Why it matters: A loose or cracked cap allows fuel vapors to escape, which throws off the emissions system.
- Check engine result: Often an easy fix — tighten or replace the cap and drive for a bit to see if the light clears.
- Failing Catalytic Converter
- What it does: Reduces harmful emissions by converting toxic gases into less harmful ones.
- Why it matters: A clogged or failing converter can reduce performance and fuel efficiency.
- Check engine result: Your car may start running rough or feel sluggish.
Please don’t ignore the light! While some causes are minor (like the gas cap), others can damage your engine or catalytic converter if left untreated.
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