What Would Make a Check Engine Light Go On? See Top Reasons

A check engine light is triggered when your car’s onboard computer or ECU detects an error coming from one of the multiple sensors on your vehicle, truck, or SUV. See top ways to resolve CEL On problem.

check engine light flashing

Though it’s often assumed that the check engine light (CEL) is a sign of a major mechanical issue, this is not always the case. In fact, according to many professional mechanics, a warning light can be produced by a minor electrical glitch.

Still, anytime a CEL illuminates on your dashboard, it is something that should not be taken lightly. A check engine light is triggered when your car’s onboard computer or ECU detects an error coming from one of the multiple sensors on your vehicle, truck, or SUV. When this happens, the ECU produces and stores an OBD-II diagnostic trouble code, that then illuminates the CEL.

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When you take your vehicle to a mechanic, they will download these OBD-II codes to provide them a starting point to diagnose the root issue and finish the right repairs. Now that we’ve explained the why — let’s go into the reasons the CEL can light-up, and the best ways to resolve these issues.

Check Engine Light On? See Best Ways To Resolve It

One Sensor has a Loose Electrical Connection or is Worn

Believe it or not, the most common reason the CEL will light-up is because of a poor electrical connection from the ECU to the sensor. When the electrical harness is loose, frayed, damaged, or exposed, it can still send a signal to the ECU and mimic a mechanical issue.

It’s also common for sensors to wear out over an extended period of time. This tends to occur quicker with fuel and exhaust system sensors, which are exposed to hot gases and carbon deposits.

simply change the sensor and the electrical harness to resolve this type of problem.

Loose or Damaged Fuel Cap

Today’s modern vehicle, trucks and SUV’s are very carefully monitored for fuel economy and emissions. If the gas cap is either left off, spoilt, or does not maintain a solid seal, it will create less pressure inside the fuel cell.

This tells the sensor there is a damaged or loose gas cap and can cause acceleration issue and/or poor gas mileage. Additional signs of a broken fuel cap include:

  • Cap does not tighten or lock properly.
  • Car smells like fuel

What can be done to fix this issue?

Most of the time,changing the gas cap can solve the problem. However, you’ll have to contact a professional mechanic to complete a check engine light inspection in order to remove the code and reset the warning light.

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Damaged O2 sensor

The emissions system on your car is highly complex. It starts with a series of sensors that monitor the fuel/air ratio and the amount of carbon deposits issuing from your exhaust.

Since these sensors are exposed to hot exhaust and can be corroded with carbon deposits from fuel and exhaust vapor, they can get damaged rather easily. When the oxygen (O2) sensor fails, it can cause the engine to misfire, leading to poor acceleration, bad fuel economy, and more.

An O2 sensor failure will typically cause a car to fail an emissions test in most countries. Other symptoms of a failing O2 sensor include:

  • Poor gas mileage accompanied by rotten egg smell
  • Rough engine idle
  • Engine misfires

What’s the solution to this problem?

Depending on which sensor is damaged, the repair typically changed the sensor. It is seen best practice to replace all 02 sensors at the same time. When one goes out, the others are often not far behind.

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Catalytic Converter is clogged

While the O2 sensors monitor exhaust gases, the catalytic converter is made to filter exhaust before it goes out the tailpipe. It converts harmful carbon monoxide into carbon dioxide.

Like any other filter, the catalytic converter can wear out or become clogged with too much debris to be effective. When this occurs, it will create an error code and trigger the CEL.

A clogged catalytic converter can produce poor fuel mileage, engine misfiring, and even lead to internal engine damage if not changed. More signs of a failing catalytic converter are:

  • Poor fuel efficiency
  • Little acceleration when pressing on gas pedal
  • Vehicle refuses to start

How to fix this issue?

Change the catalytic converter.

Air Filter or Fuel Filter may be Dirty

Routine service and maintenance are vital for your vehicle to operate correctly and efficiently. Apart having your engine oil and filter replaced every 5,000 miles, replacing your air and fuel filters is nearly as vital.

These filters keep the fuel and air entering your engine clean, which permit your motor to burn gasoline properly. If the filters get dirty, your fuel system sensors will alert the ECU and illuminate the dreaded check engine light. Some symbols that one of these filters is clogged are:

  • Hesitating, misfiring, or stalling engine
  • Hard to start or not-starting car
  • Performance problems at different speeds
  • Reduced fuel economy

Mass Air Flow Sensor is damaged

You’re likely seeing a pattern here. In reality, most check engine lights are triggered because of fuel or emissions system issues. The mass air flow sensor or MAF is responsible for carefully mixing the right ratio of air to fuel, maintaining a clean and efficient burn inside the combustion chamber of your engine.

If the MAF is damaged, the MAF sensor will send a signal to the ECU to let you know this needs to be replaced or cleaned. A faulty mass air flow sensor can stop your engine from starting.

If your car will crank over but not light-up, this is probably the source. On top of not starting, other signs of a failing air flow sensor include:

  • Engine stalls shortly after starting
  • Hesitating engine with a heavy load and/or during acceleration
  • Hiccuping engine

How to fix a mass air flow sensor issue?

This is one of those issues that should be checked by a professional mechanic first. They can determine whether the light is caused by a damaged MAF sensor or it simply needs to be cleaned.

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