Blog Car Care Advice Check Engine Light on but the Car Runs Fine? 5 Likely Causes
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Check Engine Light on but the Car Runs Fine? 5 Likely Causes

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You recently noticed a little glowing icon on your car’s dashboard and realized it’s the dreaded Check Engine Light. Your car, however, hasn’t complained yet and runs smoothly as it used to.

Why is the Check Engine Light on, but the car runs fine?
Can you continue driving?

Keep reading to get answers to these and other questions about the Check Engine Light.

This Article Contains:

Let’s get to it!

What Does the Check Engine Light Mean?

The Check Engine Light (CEL) is a dashboard warning light that shows up when your car’s computer (Engine Control Unit) senses a problem with the engine or emission control system. The issue can be anything – a loose gas cap, a failing catalytic converter, or a faulty oxygen sensor.

The light appears as an amber engine outline that may be accompanied by a “Check Engine” or similar message on some cars. A red or flashing Check Engine Light instead of a steadily lit one signals a severe issue, such as an engine misfire, and must be addressed promptly.

While the Check Engine Light may come on along with other problems, such as low fuel efficiency and reduced engine performance, sometimes there are no symptoms.

Let’s see what could lead to such a situation.

5 Likely Reasons Your Check Engine Light Is On but the Car Runs Fine

Here’re the five common reasons that could trigger this warning light without any noticeable symptoms:

1. Loose Gas Cap

A loose gas cap can trigger a Check Engine Light, allowing fuel vapors to escape into the atmosphere. Loss of fuel vapors can cause the gas tank pressure sensor to send an evaporative leak signal to the ECU.

An ill-fitting gas cap will also let dust and grime enter the fuel tank, which can damage the fuel injectors. To know if a loose gas cap is the cause of your illuminated engine light, try tightening it — if the light goes off after a few seconds, you’ve caught the culprit!

2. Faulty Oxygen Sensor

Oxygen sensors are an important part of your vehicle’s exhaust system. The upstream oxygen sensor (O2 sensor) helps the ECU regulate the fuel supply for combustion. The downstream O2 sensor keeps track of the catalytic converter’s efficiency by monitoring the amount of unburned oxygen in the exhaust gas.

A bad downstream O2 sensor can result in a Check Engine Light without producing any other notable symptoms.

3. Bad Exhaust Gas Recirculation (EGR) Valve

The EGR valve controls how much exhaust gas diverts back to the engine. Exhaust gas helps bring down the NOx emission percentage by lowering the combustion temperature. A stuck-close EGR valve can result in a Check Engine Light while your car may run without any apparent problems.

4. Onboard Computer Malfunction

A problem with your car’s Engine Control Unit can also sometimes lead to a Check Engine Light without any other symptom. Damaged wiring between any of the sensors and the ECU can also trigger a Check Engine Light.

5. Incorrect Fuel type

A high percentage of ethanol or methanol in the fuel can trigger the Check Engine Light on your car if the engine isn’t designed to burn it. It can happen if you accidentally fill your non-flex fuel vehicle with flex fuel. This fuel type will burn differently than conventional gasoline, causing the oxygen sensor to convey an error signal to the ECU.

Next, we’ll help you get to the actual cause behind the Check Engine Light using a scan tool.

How to Diagnose a Check Engine Light?

You’ll need an Onboard Diagnostics (OBD II) scanner to read the trouble code registered by your ECU. If you don’t have an OBD II scanner, you can get your Check Engine Light diagnosed for an error code by a professional like AutoNation Mobile Service.

Here are the steps you’ll have to follow: 

  1. Make sure to turn off the engine.
  1. Locate the OBD-II port under the dashboard. It’s generally present near the steering column.
  1. Plug an OBD II scanner into the port.
  1. Follow the instructions on the scanner’s screen about the ignition key position.
  1. Enter the required information when prompted by the scanner, e.g., Vehicle Identification Number (VIN), engine type, etc.
  1. The scanner will display a few systems such as engine/powertrain, transmission, brakes, etc. Check each system for any active and pending codes.
  1. Interpret the error code displayed by the scanner. You can use an online code chart for the same.

By now, you know the probable triggers behind a Check Engine Light with no other symptoms. 

But what could have been the culprit if there were other issues too?
Keep scrolling to find out.

What Are the Other Causes for a Check Engine Light?

Here are the factors that can trigger the Check Engine Light along with noticeable symptoms like poor fuel economy and reduced engine performance:

Coming up next are a few other questions you may have about the Check Engine Light.

3 FAQs about the Check Engine Light

Here are the answers to three common queries about this warning light:

1. Can You Drive with an Illuminated Check Engine Light?

The answer is – both yes and no!

If the warning light is amber-colored and steadily lit, you can still drive your car, but it would be best to get it inspected by a mechanic promptly to avoid expensive repairs later. You should also check the gas cap to make sure it isn’t loose before heading to a mechanic.

If you notice a red or flashing Check Engine Light, it means there’s a serious problem with your car, and you shouldn’t drive it any further. In this case, you’ll have to get it towed to a service center.

2. What Are the Common Codes Accompanying a Check Engine Light?

The Check Engine Light on your dashboard may be triggered by a fault registered through the following codes:

3. When Is it Normal to See a Check Engine Light?

The Check Engine Light appears along with other dashboard lights as you turn the ignition key to the “On” position while starting the car. This is to ensure that the light is working and not burnt out. However, it should turn off after starting the engine.

This warning light also comes up when the ignition key returns to the “On” position after a failed attempt at starting the engine. Another time you get the Check Engine Light is when the engine stalls on your manual transmission car. It stays on till you start the engine again.

Wrapping Up

The Check Engine Light is a key indicator of something wrong with your car’s engine or emissions system. It’s best to get your vehicle inspected by a professional mechanic whenever this warning light appears on your dashboard to avoid serious damage. 

Will you have to risk a drive to the service center with a flashing CEL?
No, not with AutoNation Mobile Service!

We’re a mobile auto repair service that can diagnose and fix your Check Engine Light-related issues right in your driveway!

Contact us, and our expert technicians will take care of your vehicle’s dashboard lights and other problems in the best way possible.