Nissan Sentra Check Engine Light Causes & DIY Diagnostic Tips

The check engine light (malfunction indicator lamp (MIL)) is a small but important light on your Nissan Sentra’s dashboard. It can indicate a variety of issues with your Nissan engine, some more serious than others.

The most common causes of the check engine light turning on are a defective gas cap, a bad catalytic converter, a faulty oxygen sensor, or engine misfires.

Read on to know all the details about the reasons and every necessary information you should know regarding the topic.

Nissan Sentra Check Engine Light Causes & DIY Diagnostic Tips

Does The Check Engine Light Lit or Flash?

If the check engine light is lit and doesn’t flash, it indicates that one of the engine sensors is gone out. Another case is, one of the sensors is sending the wrong signal to your vehicle’s ECU (computer).

In such situations, you can drive with the light on but it’s a must to get your vehicle checked as soon as possible. 

You can check for the problems yourself. Check if anything is loose or disconnected. We’ve listed a few likely candidates below. If you don’t see the problem, you can use your Nissan’s trouble codes for more info. And, if you don’t want the hassle, take your car to an auto shop for the solution.

And, if you see that the light is flashing, it means there’s a little time, and must pull over in no time because your car is having some serious issues.

What Causes Nissan Sentra Check Engine Light to Come On?

Of course, there are some potential reasons that are responsible for the condition. Below are the details.

Loose or Defective Gas Cap

It’s not a major issue though. A gas cap is one of the parts of sealed evaporative emission systems. And, this cap prevents the gas vapors in your car engine from escaping into the environment.

In case, you leave the gas cap loose without being conscious, there can be a fuel loss through evaporation. This will lead the exhaust gas recirculation system to malfunction and to turn the check engine light on.

These leaks in the EVAP emission control system can be large or small leaks. However, it’s not always the gas cap that’s responsible for such leaks. It can be the fittings, plastic recirculation lines, and the connectors.

But if you’re sure that it’s the gas cap, you must replace it as soon as possible.

Faulty Oxygen Sensor

An oxygen sensor works for measuring how much ‘unburned oxygen’ is in the exhaust system of your vehicle. It tells you how evenly the air/fuel mixture burns when the combustion process goes on.

Generally, oxygen sensors fail after driving 80,000 miles. When it fails, it can cause your catalytic converter spark plugs to get damaged. What else can happen? Here’s the answer:

  • A faulty catalytic converter emits nitrogen oxides, hydrocarbons, and other harmful compounds.
  • The engine may burn excessively more fuel than needed.
  • It will lead you to lose fuel economy and your vehicle may get only fewer miles per gallon.

Catalytic Converter Problems

Catalytic converters work as life- and -environmental saviors. It’s because they convert harmful emissions like hydrocarbons to carbon dioxide and water vapor.

Since it’s the oxygen sensor that monitors the performance of the catalytic converter, things get worse when there’s something wrong with the sensors.

If you think there’s a faulty catalytic converter, remember that generally, it doesn’t fail on its own. So, just removing the old one and installing a new converter might not solve the issue.

Something else can cause the converter to fail. So, make sure about which can be that ‘something else’ and take necessary action.

Here’s what can happen if you don’t get rid of a faulty catalytic converter:

  • Your car won’t pass any emission tests.
  • Things that caused the converter to damage will be getting worse and may cause the engine to fail.
  • The engine performance and fuel economy will be low.

Mass Airflow Sensor Problems

The mass airflow sensor is responsible for measuring the amount of airflow entering the engine so that the computer can adjust the air/fuel mixture accordingly. It helps the engine to determine the amount of fuel needed.

In case, there’s any leak in the sensor, the check engine light can come on. The sensors are sensitive to any contamination like water vapor, dirt, or oil. You may need to clean or replace the mass airflow sensor depending on how bigger the issue is.

If you don’t take the necessary steps, the engine performance and fuel economy can be low. Also, faulty sensors can lead to further damage to other parts as well.

Check Engine Light Codes Nissan Sentra

You don’t need to go to a Nissan dealer or car part shop to read your Nissan’s engine codes. You’ll need to the car into diagnostic mode, then check the engine code against Nissan’s list online or in your owner’s manual. Here’s how:

How to Set Nissan Sentra’s ECM in Diagnostic Test Mode II

  1. With the accelerator pedal pushed down all the way, turn on the ignition switch and wait 3 seconds.
  2. Please repeat the following steps five times in total within 5 seconds.
  3. Push the accelerator pedal all the way down.
  4. Remove your foot from the accelerator pedal completely.
  5. Wait 7 seconds, fully depress the accelerator pedal and hold it for approximately 10 seconds until the check engine light flashes.
  6. Remove your foot from the accelerator pedal completely.

You are now in Diagnostic Test Mode II.

How to Read Nissan Sentra’s Trouble Codes Diagnostic Test Mode II

Each flash indicates a digit in the engine code. For example, ‘3’ would be shown as 3 flashes. There will be a short delay (1.3 seconds) before the ECM starts to flash the next digit. Don’t worry if you miss it the first time; the pattern will repeat so you’ll have several chances. When you get the code, look it up in Nissan’s list online or in your owner’s manual.

2015 Nissan Sentra Check Engine Light Reset

Before you reset your Nissan Sentra’s check engine light, make sure you’ve completed your diagnosis. Once you reset, the memory clears.

The simplest 2015 Nissan Sentra check engine light reset method is disconnecting your Nissan’s battery for more than 24 hours. This clears the memory.

The other option is to set the ECM in Diagnostic Test Mode II, then press the accelerator pedal to the floor for at least 10 seconds.

How Serious Is The Check Engine Light Issue?

The check engine light can have a major or minor impact on your car. Below we’ll discuss them in detail.

Signs that indicate it’s a minor issue

  • No odor in or around your car
  • No unusual noise when you drive the car
  • Your car behaves just normally
  • You’re experiencing the same gas mileage as before
  • No smoke coming out of your car

Signs that indicate a severe issue:

  • You notice a severe loss of power
  • Your car has difficulty starting or doesn’t start at all
  • The gas mileage declined drastically
  • There are unusual noises like consistent knocks or rattles from the car
  • The car starts to produce smoke

Although your car is in the ‘minor issue’ category, it’s better to get it checked if you notice the check engine light frequently comes on. It will help prevent any potential damage to your car.

What If You Ignore The Check Engine Light?

As we said before, no matter whether the engine light is lit or flashing, you must get your vehicle checked as soon as possible. Otherwise, you can face the conditions below.

  • Reduced fuel economy: Malfunctioning engines are enough to reduce the fuel economy which results in more expenses in the long run.
  • Damage to other parts: Ignoring the check engine light can affect the other parts and cause you to have more expensive repairs.
  • Emission issues: There could be a problem with the emission control system when the check engine light comes on. If you leave it unchecked, the emission can increase and you may need to pay potential fines.
  • Safety issues: Yes, check engine lights can even indicate safety hazards. For example, there can be an issue with the emission system or the airbags.

For this, you must take the check engine light seriously and consult a professional mechanic to prevent bigger damage to your vehicle.

How Much Does It Cost to Diagnose Nissan Sentra Check Engine Light?

The average cost for diagnosing the Nissan Sentra check engine light is around $120. But it can vary according to which model of the vehicle you own or in which area you live.

Check Engine Light flashing Infographic


If your check engine light Nissan Sentra comes on, don’t panic! It could be something as simple as a loose or defective gas cap. There’s a good chance that you can diagnose the problem and fix it yourself.  

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William Baldwin

This Is William Baldwin, The Founder & Managing Editor of this website. Me and my team share automotive tips, tricks, and news

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Talha Atta

Talha Atta, a Mechanical Engineer and experienced technical content writer and editor at with a passion for the automotive industry.