Top Reasons for a Check Engine Light

Common Reasons Your Check Engine Light Will Come On

This guide will help you understand what are the most popular reasons for a check engine light or a service engine soon light (same thing) to come on listed in the order of popularity. After reading your trouble codes you will be confronted with the decision of fixing it yourself or having the work done at a repair shop. The trouble code tells you what part of your car or the particular sensor is having a problem. Once you understand what the problem is by the code definition the problem is pretty easy to fix most of the time. Most code reader tools will give the code definition along with the sensor, engine cylinder or system that has failed. Sensor replacement is one of the most popular problems your car will have and sometimes lucrative for your local garage.

1.

Oxygen Sensor Heater: Your car will have from 2 to 4 oxygen sensors in the engine's exhaust system which will have a small heater inside of them to help the sensor warm up. This heat helps the sensor generate a more accurate information data stream to the car's computer. Sensors will be located in two places. The first is near the rear of the exhaust manifold or toward the front of the head pipe and in front of the catalytic converter which are called upstream oxygen sensors. The second location will be after the catalytic converter. Replacing an oxygen sensor will take about 20 minutes and can be done either by lifting the hood or raising the car using a floor jack.

2.

Camshaft Angle Sensor: A camshaft angle sensor enables the rotation count of the engine's camshaft to be sent off to the cars computer which adjusts the engine's operating program. This sensor works in conjunction with the engine's crankshaft sensor. The CMS sensor is located near the top of the engine's cylinder head or in the valve cover. It will take between 15 and 30 minutes to change the camshaft sensor once the hood is open in most cases.

3.

Engine Misfire Code: Each of your car's engine cylinders is monitored by the computer which can tell when a particular cylinder is not operating correctly. This malfunction will be defined by a code which will locate the bad cylinder by number. This cylinder number is listed on the engine's intake manifold runner above its location. Though the computer will not tell you exactly what's wrong with the cylinder an engine miss-fire guide will help you correct the problem.

4.

Coolant Temperature Sensor: This sensor is designed to send the engines operating temperature information to the computer to help with adjustments made to the fuel input and ignition timing. Located in the intake manifold or cylinder head its subject to the engine antifreeze and can go bad due to the constant temperature variances of hot and cold. To replace the coolant temperature sensor the cooling system must be drained down to avoid coolant spillage.

5.

EVAP System Leak: The EVAP system in your car is designed to control raw gas fumes that are present in the gas tank and contain them inside of a charcoal canister where the fumes are then condensed back into fuel and transferred back into the tank. This system must be air tight and is powered by a small vacuum supply line connected to the engine. If you leave your gas cap off or loose it will trigger this code because of the leak created. An EVAP code will also be triggered if there is a leak in the EVAP system vacuum supply line or vapor control hoses.

6.

Exhaust System Lean: The engine's exhaust system must be free from holes and must maintain a balance of spent fuel from the engine's combustion process. If this balance is offset it will trigger the engine light. This problem can be caused by an engine misfire or cracked exhaust pipe which will take in fresh air making the system lean. To repair this kind of problem follow our exhaust system lean repair guide.

7.

Catalytic Efficiency Code: Your car's catalytic converter is designed to burn unspent fuel which is left over from the engine combustion process. When the catalytic converter looses its ability to do its job it will make the check engine light come on. When this happens you cannot clean it or pour something in the gas tank to help get it working again. The only way to repair this issue is to replace the catalytic converter with a new one.

8.

Crankshaft Sensor Failure: The crankshaft sensor is designed to count the rotations of the engine's crankshaft. This sensor makes the bottom of the list because most computers cannot tell if this sensor goes bad simply because when it does fail the engine will just stall. At this point it may or may not restart. Sometimes you can let the car sit for a while and the sensor will start working again. The reason the computer will sometimes not pick this problem up because there are many things that will makes the engine stall besides this sensor not working such as popping the clutch or running the car out of gas. When this sensor fails completely it will give a code for the bad sensor in which case the crank angle sensor must be replaced.

While many malfunctions can cause the check engine light to come on there are only a handful of them will make the car not safe to drive. Problems such as code gathering is incomplete and a lack for communication will also be a malfunction you might encounter.

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