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Why is the Check Engine Light On?

When the check engine light suddenly comes on the owner of the vehicle often has a minor panic attack. Too many people are under the impression that their vehicle is going to require massive repairs in order to keep their vehicle running right if this light comes on, but this simply isn't the case. Most issues that trigger the light are relatively small problems, but if left unchecked, they will result in much more extensive damage, as this first issue demonstrates.

Catalytic Converter

If it is found that the catalytic converter is in need of repair or replacement, which can be quite spendy, it is likely because a sensor or some other inexpensive part failed beforehand, which would have triggered the light long ago. The catalytic converter is an integral part of the exhaust system that converts hazardous exhaust fumes to less harmful emissions.

MAF Sensor

The mass air flow sensor is located near the front of the vehicle. It monitors incoming air and calculates how much of it needs to be mixed with the gasoline to create a proper running engine. If it fails it will result in an excess amount of fuel being burnt, leading to decreased performance and fuel efficiency.

O2 Sensor

The oxygen sensor is located in the exhaust system and monitors how much oxygen is in the exhaust fumes so that it can help assist in figuring out how much gasoline should be burnt. If it fails it too will cause too much gas to be burnt, which also contributes to a malfunctioning catalytic converter.


Misfiring means that the engine is not running quite right and that one or more cylinders is not firing or firing at the wrong time. This is usually caused by worn or corroded spark plugs or spark plug wires or ignition issues.

Loose/Broken Gas Cap

The best thing that you can hope for is that you simply forgot to tighten the gas cap after your last fill up. Or perhaps, the gas cap is broken. Either of these could allow fuel vapors to evaporate up the filler hose, which would trigger the check engine light thanks to the EVAP system.

If your check engine light comes on be sure to get to a repair shop right away. For expert check engine light diagnostics in Morgan Hill head to Fred's Foreign and Domestic Car Repair. We offer full service auto repair for all makes and models. Come find out we've been a local favorite for more than 30 years. The next time you need auto repair or auto repair in Morgan Hill or the surrounding communities give Fred's a call at (408) 706-7318.

Freds Foreign and Domestic Car Repair Blog
Written By Brian Corey
Published By MORBiZ

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