You’re cruising along, everything seems fine, and then – bam! – your car’s check engine light comes on. Suddenly, you’re wondering: Is this a quick fix or a major issue?
Your car’s check engine light (CEL) is a catch-all alert from its onboard diagnostics system that illuminates when there's an issue with a system that doesn’t have a dedicated warning light. The good news is that many of the most common causes are relatively simple fixes.
Our Tinker experts are here to help you pinpoint the problem. Here are the six most common problems that trigger a check engine light, presented from the easiest to fix to the most difficult.
1) Check Your Gas Cap
A missing, loose, cracked or worn out gas cap will illuminate your check engine light. The gas cap plays an important role in your car’s fuel system, both in maintaining pressure in your fuel system and preventing polluting vapors from escaping. If it’s loose or faulty, the system is compromised.
Luckily, this is a very easy fix. Start by making sure the gas cap is screwed on tightly – twist it until you hear a click. If that doesn’t turn the CEL off after a few drives, you may need to replace the cap with a new one.
2) Oxygen Sensor Malfunction
A malfunctioning oxygen (O2) sensor is another common reason for a check engine light to appear. O2 sensors keep tabs on the engine's performance by sampling oxygen levels in the exhaust. This is another issue that impacts both vehicle performance and environmental impact. If a sensor goes bad, it can send incorrect data to the car’s engine control unit, leading to decreased power and fuel economy, increased emissions and even engine damage if left unchecked.
On most cars, replacing an O2 sensor is a straightforward DIY job. They're typically located along the exhaust system and can be removed with a basic wrench or an O2 sensor socket.
3) Dirty Mass Airflow Sensor
The mass airflow (MAF) sensor measures the amount of air entering your engine and helps the engine management system adjust the air-fuel mixture for ideal combustion. Over time, the MAF sensor can become fouled or damaged, resulting in inaccurate readings. This can cause poor fuel economy, rough idling or even stalling, and it usually trips a check engine light.
In most cars, the MAF sensor is located near the air filter box and can be easily removed with a few basic tools. Cleaning it with a dedicated MAF sensor cleaner often resolves the issue. But if the sensor is damaged, it will need to be replaced.
4) Spark Plug or Ignition Coil Failures
Spark plugs and ignition coils work together to ignite the fuel and air in the engine’s cylinders, creating the combustion that powers the car. When either of these components fails, it can cause misfires, leading to a check engine light. Common symptoms of a bad spark plug or ignition coil include rough idling and poor acceleration.
Fortunately, replacing spark plugs and ignition coils is a job most DIYers can handle. Spark plugs are located along each cylinder bank, and ignition coils are usually mounted on top of them. Both components can typically be swapped out with basic hand tools.
5) Vacuum Leaks
The engine relies on a sealed vacuum system to regulate air intake, optimize the fuel mixture, and control emissions. When a vacuum leak occurs, too much air enters the engine, causing an imbalance that can illuminate the CEL. Symptoms include rough idling, hesitation and hissing noises from the engine bay.
Detecting a vacuum leak can be tricky, but a visual inspection of the vacuum hoses for cracks or disconnections is a good place to start. If the leak isn’t obvious, a smoke test – where smoke is pumped through the system – can reveal hard-to-find leaks.
6) Catalytic Converter Issues
Your car’s catalytic converter reduces harmful emissions by converting toxic exhaust fumes into less harmful gases before they exit the tailpipe. When the catalytic converter starts to fail, it can cause the engine to run inefficiently, activating the CEL. A telltale sign is a rotten egg smell from the exhaust.
Replacing a bad catalytic converter is a job for an experienced DIYer with the right tools. It typically involves unbolting or cutting the old converter out of the exhaust system and then bolting or welding a new one into place.
Using an OBD-II Code Scanner
With so many potential causes for a check engine light, it's highly beneficial to use an OBD-II code scanner to identify the underlying issue. Yes, the same type of scanner that many states use to inspect your engine performance each year. This tool plugs into your car’s OBD-II port, usually found under the dashboard or in the center console near the shifter, and reads the diagnostic trouble codes (DTCs) stored in the vehicle’s computer.
Once you have the codes, a quick search online or through the scanner’s reference manual will specify the malfunctioning system. From there, you can investigate further and solve the issue.
Don't have a code scanner? No problem. Many auto part stores offer free code-scanning services.
Still have questions? Speak to one of our Tinker Experts today!