Learn to Diagnose and Fix the Codes Behind the Check Engine Light
Is your service engine soon light on? This light has a few different names, like “check engine light,” but all the service engine soon lights have the same function. They let you know there is something wrong with your car.
Not sure what it means or what to do? Find out why the check engine light comes on, what it means when the check engine light is on, and how to fix a check engine light with these tips from our mechanics.
What Is the Purpose of a Check Engine Light?
A check engine light (CEL), also known as a malfunction indicator light (MIL), diagnostic trouble code light (DTC), or a service engine soon light (SES), is a warning light that turns on when the vehicle has identified a mechanical or an electrical problem with the engine, traction control, ABS system, transmission system, or the four-wheel drive system.
A check engine light icon may look different depending on the vehicle. It can look like an engine outlined in orange, an engine outlined in orange with the word “check” underneath, or the words “service engine soon,” “check engine light,” or a similar variation.
A check engine light is not the same as a maintenance light or a service light, which means the vehicle needs an oil change. Maintenance lights or service lights can look like a wrench or an oil can.
How Do I Know What Turned on the Check Engine Light?
A scan tool is needed to find out why the service engine soon light is on. The scan tool will scan and read the codes, and the codes will help direct you to the problem to diagnose it.
Is It Safe to Drive with a Check Engine Light?
If the check engine light appears solid and is not flashing, it’s usually okay to drive with the check engine light on but it’s best to get it checked out asap.
If the check engine light is flashing, pull over and have the vehicle towed. Driving with a flashing check engine light could cause more damage and cause more expensive repairs.
If the check engine light is not flashing, it’s best not to drive the vehicle and to scan it with a scan tool to find out why the check engine light came on.
Can a Check Engine Light Appear for No Reason?
There is always a reason why the check engine light comes on. It could be something as simple as a loose or faulty gas cap or a battery that needs to be charged and has low voltage. The vehicle has sensors placed throughout that the computer monitors. When a sensor fails to read or has a bad reading, the check engine light will come on. One of the more common sensors to fail is the O2 or oxygen sensor.
What If the Check Engine Light Goes Out?
If the check engine light turns off on its own, the computer is no longer detecting a problem. This can happen for various reasons, such as the temperature causing a part to seal or unseal, affecting its performance and reading, or a low voltage condition, like letting the vehicle sit for an extended period (like a month) before driving it, that turns off the check engine light once power is restored.
A check engine light turning off on its own does not always mean the problem is fixed.
Can I Turn Off or Reset a Check Engine Light?
You can turn off the check engine light by clearing the code with a scan tool. If no parts were diagnosed or fixed, it will reappear.
Do I Need to Reset the Check Engine Light after a Repair?
After the problem has been diagnosed and the repair has been completed, then you can clear the code, which will turn off the check engine light. It will also turn off on its own after a number of engine warm-up cycles without the problem occurring. The number of warm-up cycles will depend on the year, make and model of the vehicle. It can require as many as 50 cycles on some vehicles.
If There Is Still a Problem, How Soon Will the Check Engine Light Return?
The vehicle should not throw a check engine light if the problem was fixed. If the light returns, the wrong part may have been installed or the part installed might require a readiness test.
What Is Readiness Status?
Monitors within the vehicle computer will perform tests to confirm the engine systems are all working properly. If the part fails to pass these tests, the check engine light will return.
Can I Pass a State Inspection with a Check Engine Light on?
You cannot pass a state inspection with a check engine light on.
Can Clearing a Check Engine Light Help Pass State Inspection?
Clearing a check engine light will not help your vehicle pass state inspection. For example, certain states have emissions tests that require the vehicle to be hooked up to a machine. If the readiness monitors on the exhaust system have not passed their tests, it will not pass inspection and clearing the check engine light before the test will not help it pass.
Can a Check Engine Light Come on if I Am Low on Oil?
Low oil should not be a direct cause for the check engine light to appear, but if the oil level is low enough where air bubbles can travel throughout the system, an oil pressure sensor or low oil sensor can trigger a check engine light.
Newer engines with variable valve timing (VVT) are sensitive to the oil level. If the oil level falls too low, the lack of pressure is going to affect the VVT system and the timing chain system and cause components to wear out and signal a service engine soon light to trigger. In this case, changing the oil will not usually fix the check engine light.
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