If your Check Engine Light (CEL) or Service Engine Soon Light is on, it means your vehicle’s onboard computer has detected a problem. This can range from minor issues like a loose fuel cap to major engine, transmission, or emissions faults. Even if the car feels fine, the light should not be ignored, as it can indicate hidden problems that could worsen over time.

What does it mean if the Check Engine Light is on?

The Check Engine Light is triggered by your car’s ECU (Engine Control Unit) when it detects a fault in the engine, emissions, or transmission system. The severity can vary — sometimes the light stays steady (non-urgent) and sometimes it flashes (urgent, requiring immediate attention).

Common causes of the Check Engine Light

• Loose or faulty fuel cap
• Faulty oxygen sensor
• Failing catalytic converter
• Worn spark plugs or ignition coils
• Mass airflow (MAF) sensor issues
• Vacuum leaks or exhaust leaks
• Transmission-related faults

Why do you need to fix this problem quickly?

Even if the car seems to drive normally, the Check Engine Light often signals increased emissions, poor fuel economy, or gradual engine damage. Ignoring the light can lead to more expensive repairs and possible Warrant of Fitness (WOF) or emissions test failure.

How do you know when to get it checked?

You should book an inspection if:

• The light stays on for more than a day
• The light is flashing (indicating urgent misfire or emissions fault)
• You notice poor performance, rough idling, or reduced fuel economy
• There are strange noises, smells, or smoke from the engine

What happens during an assessment?

A mechanic will:

1. Connect a scan tool to read ECU fault codes
2. Interpret codes to identify possible issues
3. Perform visual inspections of sensors, wiring, and components
4. Check spark plugs, ignition coils, and fuel delivery if relevant
5. Test emissions system, including oxygen sensors and catalytic converter
6. Provide a diagnosis and repair recommendations

How much does it cost to fix?

Diagnosis typically costs $100–$180. Minor fixes such as replacing a fuel cap or sensor can cost $150–$400. Larger repairs, such as catalytic converter or transmission faults, may range from $800–$2,500+.

Is it unsafe to drive with the Check Engine Light on?

If the light is steady and the car feels normal, it’s usually safe for short trips — but it should still be checked soon. If the light is flashing or the car is running poorly, it may cause severe engine damage and should not be driven until inspected.