Check Engine Light on But Car Engine Runs Fine

Modern cars have the check engine light on to notify drivers of onboard diagnostic trouble detected by the system.

At times, the trouble detected by the check engine light might be severe, minor, or may not be significant.

Suppose your check engine light is on, but your engine runs fine. In that case, it’s likely associated with a faulty sensor, a lousy gas cap, a faulty catalytic converter, or transmission issues.

Most car owners have asked the “check engine light on, but car engine runs fine” question on Reddit because they don’t know if to panic or continue driving.

The check engine light might even go off after some time when the system resets itself, but it’s essential you know the main reason why your engine light will come on, but your car engine runs perfectly.

Table of Contents

How does the Check Engine Light Work?

Vehicles manufactured after the 80s have an onboard diagnostic system installed on them. Using sensors helps transmit the status of the power train, chassis, body, and other car components to the driver.

Also, car manufacturers have specified reading programmed into the sensor for regular car operation.

The check engine light comes on when one or more sensors send inaccurate readings to the diagnostic system.

The light might be yellow, orange, or red depending on the severity of the issue; most times, the check engine light might also start blinking.

Once the onboard diagnostic system gets notified of this trouble, the check engine light will illuminate and throw a trouble code to the OBD-II Port.

This notifies the driver that there’s trouble stopping their car engine from running fine, leaving them with the option of deciphering the error code with an OBD-II scanner or taking the car to a mechanic.

However, the check engine light might be turned on in some cases, and the car will still be running fine without any misfiring, stalling, noise, or knocking.

In the following subheading, I’ll show you possible reasons why your check engine light is on, but your car runs fine.

Check the Engine Light On, But the Car Engine Runs Fine

If you’re driving on the highway and the check engine light comes on, it’s advised that you don’t joke with your baby’s health.

You must park your car and run a proper diagnosis on it before hitting the road, well, except in cases where you’re far from home or a mechanic.

If you can drive for an extended mile and the engine is still running – OK, but if the reverse is the case, you’re in for it.

Nevertheless, if you’ve read the cause of the diagnostic trouble code using an OBD-II scanner earlier and implemented the fix, the check engine light remains. In contrast, the engine runs fine that’s another issue.

Below are reasons why your check engine light will illuminate, but your car engine runs fine.

1. A Bad Gas Cap

There are sensors in place in the gas cap to ensure there’s no gas leakage and it’s sealed properly.

If these sensors detect looseness or gas evaporation, a symptom of a bad gas cap, it’ll illuminate the check engine light.

In this case, your car engine will still run fine, but you’ll likely encounter reduced gas mileage due to the escape of gas from the cap.

You can tighten your gas cap or get a replacement from any nearby auto store.

2. A faulty Catalytic Converter

Catalytic converters are primarily found in your car’s exhaust and aid in converting poisonous gas into less toxic gases.

This component tends to encounter failure as it ages, thereby causing the sensors in the exhaust system to give off incorrect signals to the drivetrain.

This will, in turn, on the check engine light. You can replace your Catalytic converter to resolve this.

3. A Bad 02 Sensor

Besides illuminating the check engine light, a faulty 02 sensor causes misfiring, idling and, reduced gas mileage, inspection failure.

The primary function of an 02 sensor is to monitor the ratio of oxygen to gas and forwards the data to the system.

You can fix this by replacing the bad 02 sensors with a new one.

4. Low Gasoline Level

The check engine light will turn on if your gas level is below the recommended reading. While your car engine will still run fine, it’ll likely stop if not attended to.

You can fix this by fueling your tank to a recommended gas level.

5. Transmission components failure

A car consists of components such as the air pumps, EGR, sensors, etc.; once transmission components fail, the check engine light will come on.

You can decipher the cause of a check engine light using an OBD-II scanner.

6. Clear Codes on the OBD-II scanner

If you’ve implemented the fix to the problem and the check engine light is still on when you start your car, you must reset the system.

There are two ways to go about clearing codes on your car system: using an OBD-II scanner or disconnecting your battery terminals.

Using an OBD-II scanner;

Connect the OBD-II to the data port beneath the dashboard
Go to your fault code logs
Click on “Clear Fault Code” or error codes (depending on your scanner)

This should clear the check engine light if the problem has been resolved.

Now, you can also achieve this by disconnecting the terminals of your battery and waiting for some time before reconnecting it.

This will drain the power from the system and reset it when you restart the engine.

FAQs

Why is my check engine light on, but the car drives fine?

Suppose your check engine light is on, but your engine runs fine. In that case, it’s likely associated with a faulty sensor, a lousy gas cap, a faulty catalytic converter, transmission issues, a low gas level, or an error in the system.