Skip to content

Why Is Your Car Engine Light On?

As a car driver, you should have relevant knowledge about vehicle breakdowns. It's never good news when the car engine light (CEL) comes on in your car. There may be small problems or big problems!

Is the CEL lit or flashing?

First of all, we need to know, under what circumstances, your car's CEL will light up!

If the CEL flashes, the gas cap may be loose, the sensor, wiring, or connector may be faulty.

If the CEL is always on, the most likely reason is that the engine sensor is broken.

It is still possible for the vehicle to continue driving with the light on or flashing, but for safety reasons, assuming the car is running and driving well, you should stop driving as soon as possible, pull over to the side of the road and check it.

5 Reasons Why Your Check Engine Light Might Come On

1. Oxygen (O2) sensor failure

Your oxygen sensor measures the amount of unburned oxygen in your vehicle's exhaust system. It indicates how thoroughly the air-fuel mixture burns during the combustion process.

Oxygen sensors also have a tough life at +800 degree exhaust temperatures and are prone to failure at 80,000 miles or more.

If your O2 sensor fails, the car engine will burn more fuel than it needs, and you will lose fuel economy and get fewer miles per gallon. It can also damage your spark plugs and catalytic converter.

2. Loose, damaged or missing air cap

Your gas cap is part of a sealed evaporative emissions system that recirculates gasoline vapors in the tank and prevents them from escaping into the air.

If you accidentally leave the gas cap closed, the diagnostic system will quickly set the check engine light code. These leaks in the EVAP emission control system are generally classified as "small" or "major" leaks.

Loose, damaged or missing gas caps will easily cause fuel loss, and the recirculation system will not function properly. The CEL can only be used normally after being repaired.

3. Bad catalytic converter

Your catalytic converter helps protect our environment by superheating hydrocarbons and other harmful tailpipe emissions into compounds like carbon dioxide and water vapor.

Failing catalytic converters are often difficult to fix by replacing the converter yourself and can cause another converter to fail.

A bad catalytic converter can cause a vehicle to fail emissions tests, greatly reduce performance and fuel economy, and worsen further, harming the car's engine.

4. Mass airflow sensor or intake duct

Your mass air flow sensor (MAF) measures the amount of air entering the engine to determine the amount of fuel required to run the engine properly. The light will be triggered if there is any leak before or after the mass airflow sensor in the intake tract.

Mass airflow sensors are sensitive to oil, dirt, and water vapor, and any contamination on them will trigger the light. Sometimes, cleaning the sensor with intake or mass airflow sensor cleaner can solve the problem. Other times, simply replacing the sensor is enough. Be sure to check the intake duct carefully for leaks, tears, or damage.

5. Misfire

If your car stalls, you probably aren't asking yourself "why is my check engine light on?" Your spark plugs ignite the air/fuel mixture in your vehicle's combustion chambers, but if the timing of the spark, the mixture of fuel, and the compression of the mixture don't Perfect and you'll be on fire. Multiple problems can cause one cylinder to misfire or multiple cylinders to misfire.

Defective ignition coil: (DIS or coil on plug). A quick trick to determine if a coil is causing the misfire is to simply move the coil and swap it with another coil on the engine.

Defective fuel injectors: If the fuel injectors can't deliver the right amount of fuel to the cylinders, misfires can occur. Unlike swapping an ignition coil with an adjacent coil, injectors are more difficult to move.

Vacuum Leaks: Vacuum leaks often result in multi-cylinder misfires, or lean running conditions. They are also difficult to diagnose.

Worn spark plugs and/or wires: Sometimes a spark plug can exceed its useful life and fail, causing a misfire. On vehicles with spark plug wires, a defective wire or wires can also cause this. For many drivers with older vehicles, this can be the reason why the check engine light comes on.

Poor Compression: Burning or bent valves, worn piston rings, or closed valve timing can also cause misfire. These problems are more severe and all become apparent during engine compression testing.

As a driving tool, the car has many sophisticated and intelligent parts built in. Whether you are a DIY enthusiast, a home repairman or a professional repairer, you should pay attention to car maintenance knowledge, carry out maintenance inspections on the car in time, and raise awareness of hidden dangers.

Autel Scanner car diagnostic tool will help every car user to choose the most suitable Autel diagnostic scanner tool for different purposes and different budgets.

Next article The Importance of Automotive Transmission Testing

Latest Posts

  • Autel Ultra EV
    January 11, 2023

    Best EV Diagnostic Tool: Autel Maxisys Ultra EV

    Autel Maxisys Ultra EV, the best tool for electric vehicle diagnosis. A new generation of scanning diagnostic equipment capable of intelligent diagnosis of electric, hybrid, gasoline and diesel vehicles, Autel MS Ultra EV is a combination of Autel MS Ultra and EV Diag Kit.
    Read now
  • Autel MaxiIM IM508
    December 6, 2022

    IM508 Update Introducing: IM508S

    Autel brings an upgraded version of IM508 with effectively improved processing chip and customized Android version at the end of 2022. IM508 II product supports 5.0Ghz wireless network link, IM508S is one of the great breakthroughs achieved based on IM508.
    Read now