9 Common Reasons Your Check Engine Light Is On

As you drive your Mercedes-Benz vehicle around Rancho Cucamonga, do you notice that your check engine light is on? Your check engine light coming on doesn’t automatically mean that there’s something significantly wrong with the engine. That being said, it’s important to figure out why your check engine light is on as soon as possible. 

Mercedes-Benz of Ontario covers some of the most common reasons why your check engine light could be on and what to do if you see your check engine light on your dashboard. 

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Most Common Reasons Your Check Engine Light is On

1. Gas Cap

• Function: The gas cap regulates engine pressure and keeps fuel vapors from leaking. 

• Reason for Check Engine Light: The gas cap not being tightly secured can cause the check engine light to come on. 

• Possible Solution: Try unscrewing the gas cap and re-tightening it back on. 

2. Oxygen Sensor

• Function: The oxygen sensor monitors the amount of unburned oxygen in the exhaust. 

• Reason for Check Engine Light: If the oxygen sensor picks up a drop in the exhaust oxygen levels, the check engine light will come on. 

• Possible Solution: If you see the check engine light on for this reason, we recommend scheduling service right away. 

3. Catalytic Converter

• Function: The catalytic converter converts carbon monoxide and other exhaust gasses into less harmful materials. 

• Reason for Check Engine Light: A malfunctioning catalytic converter can cause your check engine light to come on. 

• Possible Solution: If you see the check engine light on for this reason, we recommend scheduling service right away. 

4. Mass Airflow Sensor

• Function: This component determines how much fuel is needed based on the amount of air going into the engine. 

• Reason for Check Engine Light: A faulty mass airflow sensor can cause the check engine light to come on. 

• Possible Solution: If you see the check engine light on for this reason, we recommend scheduling service right away. 

5. Spark Plugs & Wires

• Function: Your Mercedes-Benz vehicle’s spark plugs and wires create the initial spark that creates the combustion process to start the engine. 

• Reason for Check Engine Light: Worn-out spark plugs and wires can cause the check engine light to come on. 

• Possible Solution: If you see the check engine light on for this reason, we recommend scheduling service right away. 

6. Aftermarket Alarm

• Function: An aftermarket alarm is a car alarm that’s not an OEM Mercedes-Benz brand part. 

• Reason for Check Engine Light: Because it’s not an OEM part, an aftermarket car alarm may not be able to be installed properly, causing the check engine light to come on. 

• Possible Solution: We recommend replacing this component with an OEM car alarm designed to fit your Mercedes-Benz. You can get the OEM parts you need from our parts store. 

7. Vacuum System

• Function: This component does a lot of things, including lowering the level of harmful emissions and working with the brake booster. 

• Reason for Check Engine Light: A malfunctioning or leaking vacuum system can cause the check engine light to come on. 

• Possible Solution: If you see the check engine light on for this reason, we recommend scheduling service right away. 

8. Exhaust Gas Recirculation Valve 

• Function: The exhaust gas recirculation (ERG) valve lowers the amount of nitrogen oxide coming out of your vehicle and helps your vehicle run more efficiently.

• Reason for Check Engine Light: If the ERG becomes clogged or fails, this can set off the check engine light. 

• Possible Solution: If you see the check engine light on for this reason, we recommend scheduling service right away. 

9. Dead Battery

• Function: Your car’s battery powers the electrical components of your car and is part of starting your car. 

• Reason for Check Engine Light: There are many reasons the battery can cause the check engine light to come on, with one of the most common reasons being that the battery needs to be replaced. 

• Possible Solution: If your battery needs to be replaced, schedule service at Mercedes-Benz of Ontario to have your battery switched out for a new one. 

These are just some of the reasons why your check engine light might be on as you drive around Fontana. If you’re unsure why your check engine light is on, have our expert technicians diagnose your vehicle. 

What to Do if You See a Flashing or Blinking Check Engine Light

It’s one thing if you see your check engine light on, but what about a flashing check engine light? If you see your check engine light flashing, it usually means something requires immediate attention. 

Here’s what Mercedes-Benz of Ontario recommends if you see a flashing check engine light: 

• Check Your Vehicle: Check to see if there are any visible signs of what could be causing your check engine light to blink. These can include lights, gas, smoke, sounds, etc. 

• Reduce Engine Demands: Try lowering your speed and driving with a lighter load until you get to a service center near Chino. 

• Use Mercedes me: The Mercedes me app can run a diagnosis on your vehicle remotely. This can help you determine what might be causing the check engine light to blink. 

How to Reset Your Check Engine Light

Sometimes, you may still see your check engine light on your dashboard even after you’ve already had it serviced. In this case, it may need to be reset. 

Here are some simple steps you can take to reset your check engine light: 

1. Put your key into the ignition, and turn it to the “On” position without starting the engine. 

2. Push the lower left button on the left side of the steering wheel. 

3. You should see the reason why the check engine light was showing on your dashboard. 

4. If you push the same button, you should see the mileage. 

5. You should be able to find the reset button on the left side of the instrument cluster. 

6. Hold down the reset button until you see a display that says “To reset: press the reset button for 3 seconds.” 

7. Push the reset button until it says that the system has been reset. 

If your check engine light is still flashing, schedule service with our team near Corona to get it taken care of. 

Schedule Service in Ontario With Us

If you need routine service or major repairs for your Mercedes-Benz vehicle, contact Mercedes-Benz of Ontario. We can have your vehicle ready to be back out on the roads of Inland Empire in a timely and efficient manner. Don’t forget to ask about our service specials before you visit us.