If your Check Engine Light (CEL) is on, it means your car’s computer has detected a problem with the engine, emissions, or transmission system. While the car may still run, the issue can range from something minor, like a loose fuel cap, to serious engine or emissions failures. It’s important to have the light checked as soon as possible to prevent further damage.

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

The Check Engine Light comes on when the Engine Control Unit (ECU) detects a fault through its sensors. A steady light usually indicates a non-urgent issue, while a flashing light means there’s a serious fault — often an engine misfire — that requires 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 or exhaust leaks
• Transmission or emissions system faults

Why do you need to fix this problem quickly?

Even if your car feels fine, the Check Engine Light often means reduced fuel efficiency, higher emissions, or hidden damage. Ignoring it could lead to costly repairs and 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 (urgent misfire or major fault)
• The car is running rough, stalling, or losing power
• You notice unusual smells, smoke, or poor fuel economy

What happens during an assessment?

A mechanic will:

1. Use a scan tool to read fault codes from the ECU
2. Interpret codes to narrow down possible issues
3. Inspect sensors, wiring, and key components
4. Check ignition, fuel delivery, and emissions systems
5. Test drive the car to confirm performance
6. Provide a clear diagnosis and repair plan

How much does it cost to fix?

Diagnosis usually costs $100–$180. Simple fixes such as replacing a sensor or fuel cap cost $150–$400. Larger repairs, like catalytic converter or transmission issues, 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, short trips may be safe — but it should be checked soon. If the light is flashing or performance is affected, driving further could damage the engine, and the car should be stopped and inspected immediately.