Why does my car run fine even with the Check Engine Light on?

The check engine light is generally a warning sign on a vehicle’s dashboard, commonly called the malfunction indicator lamp (MIL). When the light comes on, it means there is a malfunction with one or more engines, emission control, or connected systems. Various faults, from simple ones like a loose gas cap to more critical ones like a broken oxygen sensor or catalytic converter, might trigger the check engine light to come on. Software flaws in the vehicle’s onboard computer or electrical problems may cause the light to come on. The performance and safety of the car might be significantly impacted if the check engine light is disregarded.

Possible Causes

  • Loose or faulty gas cap causing minor emissions issues.
  • Old spark plugs or spark plug wires need replacement.
  • Faulty oxygen sensor impacting fuel economy but not performance.
  • Catalytic converter problems, may not affect short-term driving.
  • Mass airflow sensor malfunction affects fuel injection, but it is not always noticeable.
  • Intermittent issues that don’t immediately impact engine performance.

Possible Solutions

  • Check Gas Cap: Ensure it’s tight; a loose cap can trigger the CEL.
  • Read OBD-II Codes: Use a scanner to identify specific error codes.
  • Inspect Common Issues: Look for obvious issues like loose connectors or damaged hoses.
  • Routine Maintenance: Ensure regular maintenance like oil changes and air filter checks.
  • Professional Diagnosis: If unsure, consult a mechanic for a thorough check-up.

Related: Why is the RPM fluctuating while driving?

Significance of the check engine Light

Even if the vehicle is operating normally, an engine or emission control system issue might result in higher emissions, decreased fuel efficiency, and even engine damage. Ignoring the check engine light might result in expensive repairs later on, as well as having an impact on how well the car performs now. Minor problems discovered early can frequently be repaired relatively cheaply, but if ignored, they can grow to become much larger and more costly fixes. It’s crucial to remember that the check engine light does not always indicate that the automobile is in immediate danger or that the engine will soon fail.check engine Light

The check engine light is on, but the car runs fine. Why?

There are a bunch of occasions behind the yielding of the check engine light, even if the car seems to be running fine. Here are some of the top causes behind this, 

Loose and damaged gas cap

The check engine light happens due to a loose or damaged gas cap. This is one of the most frequent and simplest fixes for the light’s on-off problem. In many cases, the issue can be resolved by simply tightening the gas cap or replacing it if it is damaged. The oxygen sensor modifies the fuel-to-air ratio according to the amount of oxygen found in the exhaust fumes. The check engine light may illuminate if the oxygen sensor is malfunctioning. Although the car might initially function without a problem, a damaged oxygen sensor can eventually result in reduced fuel efficiency and elevated emissions.Loose and damaged gas cap

Failing catalytic converter

Hazardous exhaust gasses are transformed into less hazardous pollutants by the catalytic converter. The check engine light could come on if the catalytic converter is malfunctioning. As a result, the car may eventually fail emissions tests due to higher emissions and decreasing fuel efficiency. The MAF sensor adjusts the fuel-air ratio following the amount of air entering the engine. The check engine light may come on if the MAF sensor isn’t working properly. Fuel economy and performance may suffer as a result of this.Failing catalytic converter

Damaged alternator

The check engine light illustrates a malfunctioning alternator or dead battery. This is because the car’s internal computer requires a steady flow of power to operate. Failure of the alternator or battery may result in the computer malfunctioning and turning on the check engine light.Damaged alternator

Faulty spark plugs with bad ignition coils

The spark plugs and ignition coils ignite the engine’s fuel. The check engine light comes to light if one or more of them is broken. Inadequate maintenance may result in diminished performance, poor fuel efficiency, and sometimes even engine damage. If the engine overheats, this could result in damaged engines and poor performance and fuel economy.bad ignition coils

Faulty EGR valve

The check engine light sometimes comes on if it is malfunctioning. This might result in higher emissions, poorer performance, and less efficient fuel use. Remembering that a check engine light might appear for a wide range of causes is ideal for getting it examined by a licensed mechanic as soon as possible. It’s preferable to be safe than sorry because disobeying the warning could result in later, more significant issues.Faulty EGR valve

How to diagnose and fix this problem?

It is usually preferable to have a competent mechanic perform the work because diagnosing and correcting common check engine light issues can be complicated. Nonetheless, you can follow the following general procedures to identify and resolve typical check engine light issues,


Some sensors and engine parts activate the check engine light, and the onboard computer saves a diagnostic trouble code (DTC) to help locate the problem. A mechanic can use a diagnostic scanner to extract the DTC and eliminate potential reasons. After retrieving the DTC, the technician can examine the components linked to the DTC to identify the underlying problem.


This can entail ensuring the wiring, sensors, and other parts are all working properly. The mechanic can test the components connected to the DTC after they have been examined to see if they are in good working order. Checking the sensors and other features may include utilizing specialist tools or equipment.


The mechanic can repair or replace the problematic component once it is located. A sensor replacement, a wiring correction, or the replacement of a part like the catalytic converter may be necessary to do this. The mechanic can clear the DTC and do a test drive to confirm that the problem has been fixed after replacing or repairing the problematic component. The repair was successful if the check engine light stayed out and the car ran smoothly.


The check engine light may illuminate due to a loose, harmed, or missing gas cap. This is because fuel vapor could escape from the fuel system and set off emissions-related codes. The gas cap can be examined by a mechanic, who can also swap it out if necessary. The mass airflow (MAF) sensor determines how much air enters the engine and provides the computer with fuel addition instructions. The check engine light may illuminate if the MAF sensor is dirty or malfunctioning.


The MAF sensor may require cleaning or replacement by a professional. The computer receives instructions from the oxygen sensor on how much fuel to add based on how much oxygen is present in the exhaust. The check engine light could come on due to a malfunctioning oxygen sensor. The oxygen sensor may need to be changed by a mechanic.


The catalytic converter lowers emissions by transforming toxic gasses into less damaging ones. The check engine light may illuminate if the catalytic converter is malfunctioning. If necessary, a mechanic can swap out the catalytic converter. Occasionally, overall performance problems can cause the check engine light to come on. Problems with ignition coils, spark plugs, or other parts may fall under this category. So repair the catalytic converter as soon as possible.

A mechanic can tune up the engine to fix these problems and ensure the engine operates smoothly. Again, it’s important to remember that diagnosing and repairing check engine light problems can be complex, and it’s always best to have a qualified mechanic handle the job. They have the expertise and tools to diagnose and repair the issue safely and efficiently.

Final words

Even if the automobile runs smoothly when the check engine light is on, several systemic problems may exist. It is crucial to take the check engine light seriously and not ignore it because it may indicate a significant issue that, if left unattended, might eventually cause the car to cease working altogether or necessitate expensive repairs.

Even though it could seem alluring to keep driving the automobile despite the problem, doing so could cause more harm to the car and put the driver and other passengers in danger. The motorist should speak with a mechanic or dealership to identify the problem and choose the best action. The car may be running fine, although the CEL persists. If you go through the entire article, then it is so possible for you to encounter such kinds of pseudo-malfunction lights.

Meet our professional car mechanic, Russell D. Steele, who has been in this field for five consecutive years and works with several automotive companies. He completed the "AUTOMOTIVE & LIGHT DUTY DIESEL TECHNOLOGY" course from NorthWest Lowa Community College, where he learned essential diagnostic and transportation management skills and became a certified mechanic.

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