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How to Troubleshoot Your Check Engine Light

BY: Larry Witherspoon Jr.
Mechanic in overalls working on a car for it's check engine light

The check engine light is often misunderstood, leading to unnecessary stress. Although it should not be ignored, a check engine light does not necessarily mean expensive engine repairs are in order. The solution could be something as simple as replacing a faulty gas cap. Let’s discuss how to diagnose and troubleshoot the check engine light when it does come on.

What Is a Check Engine Light?

Although our vehicles can’t “talk” to us to tell us when something isn’t right, cars signal for help when necessary using various dashboard warning lights and sounds. For any vehicle produced since 1996, federal regulations require that all auto manufacturers use a universal interface for these warning symbols, helping drivers and technicians alike more easily recognize and identify the mysterious dashboard warning signs. Warning lights can alert you that your tire pressure is low, it’s time for an oil change, or your vehicle is overheating.

The check engine light on is another warning indicator. When it pops up, it alerts drivers that a component within the emissions system or engine isn’t working as it should and requires immediate attention. It can light up as solid yellow, orange or red, or it can blink. The issue is likely not urgent if the light is illuminated but solid. However, if you see a blinking check engine light, this is potentially catastrophic. Safely pull the car over, turn off the engine, and contact your roadside assistance provider for a tow to an engine repair shop.

How Does a Check Engine Light Work?

The check engine light, previously known as the malfunction indicator lamp, is part of a vehicle’s onboard diagnostic (OBD) system. The OBD is a complex network of electronic sensors that monitor and regulate all vehicle components. When a problem is detected, a trouble code is generated and stored. It can later be retrieved using an OBD-II scanner, helping car owners and technicians quickly diagnose and troubleshoot a check engine light. Once an error code is generated, the appropriate dashboard warning light is illuminated to alert the driver of the problem.

These are a few common causes of OBD-II diagnostic codes:

  • P0420/P0430 – Low catalyst system efficiency, meaning there may be a serious problem in the catalytic converter, exhaust, or fuel systems.
  • P0171/P0174 – Oxygen sensors are detecting the oxygen-to-fuel ratio is off.
  • P0101 – Mass airflow sensor issues.
  • P0300 – Misfiring cylinder.
  • P0440/P0455/P0442 – A leak in the Evaporative Emission (EVAP) system has been detected.
  • P0128 – The engine is running cooler than it is supposed to be.
  • P0172/P0175  – Too much gasoline is being detected in the exhaust system.
  • P0401 – Exhaust gas recirculation (EGR) flow is insufficient, and a valve is likely malfunctioning.

What Can Cause a Check Engine Light to Come On?

The check engine light is tied to the emissions system and the engine, which means that a check engine light could refer to anything from a loose gas cap to an engine replacement. For the most part, a solid check engine light means you’re just due for some routine maintenance.

Here are a few examples of what could trigger a check engine warning light and what could happen if repairs are delayed or ignored:

Oxygen Sensor Needs to Be Replaced

The O2 sensor measures the amount of unburned oxygen in the exhaust system. It connects with your vehicle’s electronic control unit (ECU) to determine the right air-to-fuel ratio for prime engine performance. A faulty oxygen sensor can slow acceleration and even cause you to stall. It can also reduce fuel efficiency and increase the amount of pollution put into the environment. It could result in expensive engine repairs and catalytic converter malfunctions if ignored.

The Gas Cap Is Loose or Needs to Be Replaced

We don’t often think about how often we take the fuel cap off and twist it back on. It seems minor, yet that gas cap seals up your fuel system, preventing gas vapors from escaping. When it begins to wear out or isn’t tightened well enough, vapors escape, reducing fuel efficiency and polluting the air. It also helps to stabilize the air pressure within the fuel tank. If pressure can’t normalize, additional problems could occur.

The Catalytic Converter Is Failing

The catalytic converter is a major component of your vehicle’s emissions control system. By converting 90% of harmful emissions, like carbon monoxide, into something less harmful, like steam, your catalytic converter reduces harmful airborne pollutants. When your catalytic converter clogs or fails, fuel economy and the efficiency of your car will drop, negatively impacting overall health and performance. If left undiagnosed, it could cause damage to the car’s engine, the exhaust manifold, or the underbody of the car. A faulty catalytic converter will also cause a vehicle to fail emissions tests.

The Spark Plugs Are Worn

Spark plugs emit a bolt of electricity across a small gap that ignites the mixture of fuel and air needed to start your vehicle. If they are faulty, they can cause your engine to misfire, reducing power and functionality. If ignored, this can lead to long-term engine damage.

How to Make a Check Engine Light Go Off

The check engine light can be distracting, but it is an essential reminder that your vehicle needs your attention to avoid further damage. After making the repair, it can take time for the check engine life to turn off. There are a few easy ways to reset the engine light yourself. Remember that clearing the code does not resolve the problem, and the warning light will return if the problem persists.

Here are a few ways to clear your check engine light:

Go for a Drive

The onboard diagnostics system performs periodic rechecks at regular intervals. How long it takes for a check engine light to reset itself is different for every make and model. Sometimes, simply driving around 50 to 100 miles will initiate the recheck.

Turn It On and Off

For some vehicle makes and models, the system resets itself after 10 or 20 cycles. A cycle is a period between when the ignition starts and stops, or the equivalent of turning it on and off again. In some models, turning it off and on three times in a row will manually restart the car’s computer.

Disconnect the Battery

Disconnecting the vehicle from the power source, the battery, will also reset the light. To do this, disconnect the battery’s positive connection, wait 15 minutes, then turn the ignition to the “on” position three times before reconnecting the positive battery connection.

Manually Clear the Trouble Code

A quick and easy way to effectively reset the check engine light is to manually clear the trouble code using an OBD-II code reader. These scanners are inexpensive and can be purchased at most auto parts stores. After plugging the scanner into the port under the steering wheel, you’ll need to turn the ignition into the “on” position and press the “read” button on the scanner. After you’ve read the code, you can choose “erase” or “clear.”

Troubleshoot Engine Repairs with Endurance Warranty

A check engine light illuminates for various reasons, ranging from minor to expensive engine repairs. Although it is possible to troubleshoot a check engine light yourself, having an ASE Certified mechanic or repair shop can save time and money by diagnosing and repairing the problem before it worsens. An extended warranty can help protect you from expensive auto repairs and other mechanical breakdowns.

Endurance Warranty offers customizable vehicle protection plans to fit your budget and your needs. There are even coverage plans available for vehicles not traditionally eligible for extended warranty plans, including high-mileage vehicles, older vehicles, cars with rebuilt or salvage titles, and cars used for business, including delivery and rideshare. All plans include additional benefits such as 24/7 roadside assistance and towing, rental car reimbursement, and trip interruption coverage, and are backed by a 30-day money-back guarantee. Drive confidently, knowing that you’re covered with the plan that’s right for you.

We also understand that it is important to take your vehicle to someone you trust, which is why Endurance auto protection plans do not require you to take it to a dealership for repairs. Vehicle repairs and maintenance can be completed by any certified mechanic or repair shop you feel comfortable with. When you activate Endurance Elite Benefits, you can save even more with perks like tire replacement or repairs, collision discounts, and key fob replacements.

Protect your vehicle from costly engine repairs by requesting a FREE quote or calling a member of our award-winning customer service team at (800) 253-8203 today. You can also find more answers to your frequently asked questions on our blog. Get repair tips, cost comparisons, tips to improve your gas mileage, and more.

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