Common Reasons the Check Engine Light Comes On and What to Do

The Check Engine light or Service Engine soon light is one of the most misunderstood warning lights on a vehicle dashboard.  It could come on from something as simple as a loose or cracked gas cap to a more complex issue, like a problem with the catalytic converter.  Despite what some websites will tell you, it’s not always as simple as going to your local parts store and having them check the code from your vehicle’s onboard diagnostic system.  In this post, I’ll give you some background on the Check Engine light and Service Engine Soon lights.  I’ll also identify the most common reasons this light will come on and what you should do about it when it does happen.

What is the Check Engine Light or Service Engine Light telling you when it comes on?

Your vehicle is equipped with a computer (also referred to as an Electronic Control Module or ECM) that controls how your vehicle operates.  The ECM’s job is to keep your vehicle running at optimum efficiency while also minimizing emissions.  Within the ECM is an onboard diagnostic system that is constantly evaluating the electronic sensors and emission control systems, including the catalytic converter.  When the system detects a potential problem, it turns on the Check Engine light or Service Engine Soon light on your dashboard.  The best part about this system is that it often alerts you to a little problem long before it becomes a big problem.

Why you shouldn’t ignore this light?

The whole purpose behind the Check Engine or Service Engine Soon light is to alert you to a minor problem before it becomes a bigger issue.  While you don’t need to immediately pull off the road and have your vehicle towed when this light comes on, you should schedule an appointment to have it fixed right away.  Failing to do so could cause serious damage to components like the catalytic converter and that’s an expensive part to replace.

What are some of the common reasons the light comes on and what should you do?

Reason #1 – A Loose or Faulty Gas Cap – Yes, surprisingly this can cause the Check Engine or Service Engine Soon light to come on.  This is a simple and inexpensive fix – one you can easily do yourself.  Start by taking the gas cap off and putting it back on.  You’ll then need to drive the vehicle a few times to get the Onboard Diagnostic (OBD) system to reset and turn the light off.  If the light remains on after a few drives, you may want to consider replacing the gas cap.  When doing this, you’ll want to get a cap that was specifically made for your vehicle.  Again, you have to drive the vehicle a few times for the ODB system to reset.

If you go through all these steps and the light remains on, you’ll want to schedule an appointment with Shade Tree Garage as soon as possible.  As I mentioned in the opening paragraph of this post, diagnosing the reason a Check Engine or Service Engine Light comes on isn’t as simple as getting the ODB codes read at your local parts store.  For some codes there are countless problems that could be causing the issue.  Our ASE-Certified Technicians have the training and experience to find the source (or sources) of the problem and implement a solution to correct it.

Here are some of the other common reasons that will cause the Check Engine or Service Engine Soon light to come on:

Reason #2 – Faulty Oxygen Sensor:  For your car’s engine to operate efficiently, it requires a particular ratio of oxygen to gasoline.  When there is too little oxygen, your engine will be running “rich” from gasoline that is left over from the combustion process.  Too much oxygen causes poor engine performance and can even damage the engine.  The oxygen sensor works with the engine’s computer to determine and adjust the ratio of air to gasoline.  When the sensor is faulty, the computer cannot properly adjust the air/gasoline ratio and the light comes on.  A malfunctioning sensor can cause loss of engine power and will eventually foul your spark plugs and catalytic converter.

Reason #3 – Spark Plugs & Wires: The spark plugs and wires in your vehicle wear out and need to be replaced.  Worn plugs and wires will affect the combustion process.  Plugs that are misfiring are noticeable when you accelerate – you may feel a little jolt.  Don’t wait until the spark plugs and wires are completely worn out.  Have them replaced according to the schedule recommended by the vehicle manufacturer.

Reason #4 – Mass Airflow Sensor is Faulty: The mass airflow sensor measures the amount of air going through the air filter.  It then tells the computer how much fuel is needed based on the amount of air entering the engine.  With a faulty mass airflow sensor, you notice poor gas mileage.  The vehicle may also begin to stall.  If you delay replacing the mass airflow sensor, you risk damaging the spark plugs, oxygen sensor, and/or the catalytic converter.

Final Comments About the Check Engine Light

Remember, failing to fix any issue that causes your Check Engine or Service Engine Soon light to come on can end up causing the catalytic converter to fail.  Trust me; you don’t want this to happen.  Because of the metals they use in a catalytic converter – – platinum, palladium and/or rhodium – they are very expensive to replace.

By maintaining your vehicle and taking care of small problems when they first occur, you’ll be able to avoid, or at least minimize, major repairs on your vehicle.  If your Check Engine or Service Engine Soon light is on, click here to schedule an appointment with Shade Tree Garage in Morristown, NJ.