5 Common Reasons the Check Engine Light is On

5 Common Reasons the Check Engine Light is OnIt is unfortunate that so many drivers hide from the check engine light, when in reality, they should embrace it. It is often assumed that if the check engine light comes on that the car is doomed. However, this simply isn't the case. In most circumstances, when the check engine light initially comes on it generally represents some small issue. Left ignored though, that problem will grow much, much worse, and more expensive to fix, as demonstrated by this first check engine light problem.

Failed catalytic converter

The catalytic converter is designed to convert hazardous exhaust fumes into less hazardous emissions, and if it fails, it can be very expensive to fix. It can fail if too much gasoline is being burned, among other issues, but if it is found the catalytic converter has malfunctioned when running check engine light diagnostics it is likely a much smaller problem caused it first, such as one of the following.

Malfunctioning MAF sensor

The mass air-flow sensor monitors incoming air in order to calculate how much of it should be mixed with the gasoline in the combustion chamber to ensure the engine runs properly. If it malfunctions it could result in the car running rich, meaning too much gas will be used.

Failed O2 sensor

The oxygen sensor acts similar to the MAF sensor but is located in the exhaust system, measuring the amounts of oxygen in the emissions in order to manipulate the air/fuel mixture. Again, if it fails, it can cause the car to run rich, burning excessive fuel, thus drastically dropping MPGs and damaging the catalytic converter. The O2 and MAF sensor are relatively inexpensive to repair compared to the catalytic converter.


Misfiring means that the engine is not running smooth, often indicating at least one cylinder is failing to do its job. This could be caused by failed ignition coils, corroded spark plugs or spark plug wires, and a few other issues. This problem can often be fixed quickly and at little cost, but if left unchecked it can result in much worse engine problems.

Broken or loose gas cap

One of the more surprising, and all too common, reasons the check engine light comes on is because the gas cap is simply loose, or perhaps cracked. If the cap isn't sealing the filler tube than fuel vapors can escape up it and out into the atmosphere, wasting gas before you could ever use it. This is caught by the EVAP system, which triggers the check engine light.

If you need check engine light diagnostics in Tacoma visit the professional technicians at AllTek Auto Repair. We provide high quality auto repair, diagnostics and maintenance to all makes and models. To schedule an appointment for superior auto repair in Tacoma don't hesitate to give us a call at (253) 259-3893 today.

Alltek Auto Repair Blog

Written and Published By MORBiZ