6 Reasons Why The Check Engine Light May Come On

Here are the six common reasons that can trigger the check engine light of your vehicle: 

1. Failed Oxygen Sensor

An oxygen sensor measures the unburnt oxygen in your vehicle’s exhaust system. This helps the ECM (car’s computer) to know how efficiently the fuel burns during combustion. Accordingly, the ECM creates an ideal air fuel mixture to offer optimum mileage under different driving conditions.

However, these sensors have to tolerate extremely high temperatures and are prone to fail when your vehicle crosses 80,000 miles. 

A faulty oxygen sensor can even damage your spark plugs and catalytic converter, leading to costly repairs. Your vehicle will also not pass the emission tests as a bad catalytic converter will emit harmful compounds like hydrocarbons and nitrogen oxides. 

2. Loose Gas Cap

Sometimes, an issue as simple as a loose gas cap can cause the diagnostic system to turn on the engine light. 

Your gas cap is a part of a sealed evaporative emissions system that prevents the gas vapors from escaping into the air. 

If you accidentally leave this gas cap loose, you can lose fuel through evaporation, and your exhaust gas recirculation system will not function smoothly.  

3. Weak Car Battery

When your car battery is weak or isn’t fully charged, it’ll fail to send enough power to your vehicle’s ECM. This will result in a flashing check engine light, and your ECM will register a trouble code.  

You may also notice an illuminated battery light on your dashboard, indicating an issue with your battery or alternator. When that happens, you should call your service center and schedule a battery service. 

4. Faulty Spark Plugs

Spark plugs are responsible for generating an electric spark to crank your engine. When the spark plugs are worn out, they can lead to ignition problems, fuel wastage, and even damage other essential elements of your vehicle.

Worn-out spark plug wires can also cause the check engine light to come on. In other cases, it could be the ignition coil that’s to be blamed. 

5. Faulty Mass Airflow Sensor 

The mass airflow sensor in your vehicle measures how much air enters the engine. The ECM uses this data to determine the amount of fuel to inject into the combustion chamber. 

If the sensor goes bad or there are any leaks in the air intake tract, the check engine light will come on. 

The mass airflow sensor is also sensitive to dirt, water, and oil. So, contamination in the air tract can trigger the check engine signal too. 

6. Engine Misfires

Spark plugs help ignite the air and fuel mixture in the combustion chamber. If the timing of the spark is off or if the fuel mixture and its compression isn’t right, your vehicle can misfire. 

Some other reasons that could also cause engine misfire and trigger the engine light are: 

• A defective ignition coil
• Worn spark plugs and plug wires
• A defective fuel injector

If you keep ignoring the check engine light for such misfires, they can result in serious problems like a mechanical failure of your car’s engine.

How Urgent Is A Check Engine Light Diagnosis?

A solid or flashing engine light indicates that your vehicle’s onboard computer has detected a problem, and you need to schedule service to address the issue. 

However, a flashing engine light indicates a more pressing concern that requires immediate attention. A red or orange light may come on in some vehicles instead of a yellow flashing light. In either case, it indicates an urgent issue that you should address ASAP. 

If the engine light is steady and there’s no performance loss, the problem isn’t too urgent. However, you should schedule service at your earliest to avoid costly repairs. 

How Much Does A Check Engine Light Diagnosis Cost?

An auto repair shop could charge anywhere between $88 to $144 to run a check engine light diagnosis. 

However, this cost doesn’t include the taxes and other fees a service center may charge for the diagnostics tests. The price can also vary depending on the vehicle model and the labor charges.  

Based on the check engine diagnosis, a certified technician at the dealership may suggest an engine repair or other related auto parts fixes that will cost extra. 

4 FAQs On Engine Light Diagnosis

Here are answers to some common check engine questions: 

1. What Does A Check Engine Light Mean?

The engine light (check powertrain light) is a visual indicator on your vehicle’s dashboard that comes on when there’s a problem in your Onboard Diagnostics System (OBD). 

Most modern vehicles have an Engine Control Module (ECM) that regulates the vehicle’s fuel supply, air management, fuel injection, and ignition — based on the data it receives from different sensors on your vehicle. 

Whenever the ECM runs into an issue that it can’t resolve, it triggers the Check Engine Light (CEL). 

Since the engine light can come on for numerous reasons, the ECM also logs a Diagnostic Trouble Code (DTC) detailing the issue. You can read this engine code using an OBD II code reader.

However, you’ll still require a certified technician to do a multi point inspection and find the root cause of the issue. 

2. Is It Safe To Drive With The Check Engine Light On?

If there’s no change in your vehicle’s performance, but the engine light is on, you can continue to drive until you bring your vehicle to a safe location. 

Nonetheless, drive with caution and get the issue fixed ASAP to prevent further damage to your car’s engine. 

However, if there are strange sounds from the engine, poor acceleration, or rough idling combined with a lit check engine light, don’t try to accelerate or shift gears. Slowly bring your car to a safe stop and call for roadside assistance.

If you spot a flashing check engine light, you should pull over immediately. Not doing so could damage essential elements like the costly catalytic converter and possibly create dangerous driving conditions for you. 

3. How Do I Fix The Check Engine Light? 

While it’s best to have an engine light diagnosis done by a certified technician, here are a couple of things you could do at your end:

• Try to tighten the gas cap, as it’s one of the common reasons for illuminated engine light. Tightening the gas cap should resolve the issue. 
• Inspect the dashboard for a warning light indicating low oil pressure or overheating. In that case, call your service department or mobile repair technician at the earliest. 
• Use an OBD II scan tool for reading the trouble code. If you’re using desktop software, use the keyboard navigation to view the trouble code and accordingly book the required service hours at an automotive repair shop.

Pro Tip: Mobile repair services can perform brake service, oil change service, transmission service, battery service, or tire rotation and alignment service right in your driveway. 

4. How Do I Reset The Check Engine Light? 

Resolving the underlying issue will clear the diagnostic code and reset the engine light. You can contact your dealership’s vehicle service department or an auto repair shop to help fix the issue.

If you plan to do it yourself, here are some methods: 

• Drive your vehicle until the engine light goes off 
• Disconnect and reconnect the battery
• Get an OBD-II scan tool to reset the code

Just remember that the light will come back on if the underlying issue isn’t eliminated. 

Getting a multi point inspection that includes brake service, alignment service, or oil change service can help prevent future problems.