If the computerized onboard diagnostics system, also known as the OBD II, detects a problem with the ignition, emission control, exhaust, or fuel system, the check engine light will be triggered. Depending on the severity of the problem, the light may either flash, come on intermittently, or stay on.
On most vehicles the check engine light is yellow or amber, however, some vehicles have a two-tone yellow and red malfunction indicator light. If the light is red, drivers should immediately stop the vehicle and have it towed to a certified auto service center.
The only way to accurately assess what triggered a check engine light is to have a computerized diagnostic scan done at a trusted auto repair center. Mechanics use a specialized tool that connects to the OBD II, which generates and stores the trouble code which activated the light.
The most common reasons why a check engine light comes on are:
The Gas Cap is Loose
Your gas cap is part of your vehicle’s vapor recovery system, which is linked to the emissions system. If the gas cap is loose or misaligned, it can set off an error message that may trigger a check engine code. Removing and re-installing the gas cap may re-set the error code.
You Have a Faulty Oxygen Sensor
The oxygen sensor continuously measures the amount of unused oxygen emitted from your vehicle's exhaust system. When this sensor fails, your fuel consumption will increase because your engine won't work as efficiently as it should. Over time, a faulty oxygen sensor can also cause damage to the catalytic converter, spark plugs and spark plug wires.
You Have a Faulty Catalytic Converter
The catalytic converter is an emission control device that’s part of your vehicle’s exhaust system. It is a metal canister that contains a ceramic honeycomb filter that stores and releases excess exhaust to optimize engine performance and reduce the output of harmful chemicals.
If your catalytic converter fails due to rust, contamination or a lack of regular maintenance, your vehicle won’t pass emissions testing. You may also find that your car runs rough, it may burn more fuel than normal, and it may run at a higher temperature.
Your Spark Plugs or Plug Wires Need Replacing
Spark plugs ignite the combustible air/fuel mix that your engine needs to function, while spark plug wires transfer the spark from the ignition coil to the plugs.
Over time, spark plugs can become corroded, gummed up, or misaligned, leading to poor engine performance. You may notice your engine isn’t as powerful as it once was, or that you have trouble starting your car. Problems with your spark plug wires can cause similar performance issues, and left unchecked, can damage the ignition coil, oxygen sensors, and catalytic converter.
You Need a New Mass Airflow Sensor
The mass airflow sensor (MAF) monitors and regulates the volume of air entering your engine, which in turn impacts fuel consumption. A faulty MAF can cause your engine to burn more gas than usual and damage your spark plugs and wires, catalytic converter, and oxygen sensors.
Because it’s impossible to know what triggered the check engine light, it’s always a good idea to have your vehicle checked by an auto service expert as soon as the light comes on. If the light illuminates within a few minutes of fueling up, you may want to remove and reinstall the gas cap to see if that will reset the trouble code.
In general, if the engine light is flashing, you should stop driving and call an auto repair center right away. Continuing to drive while the check engine light is blinking can seriously damage your vehicle and leave you stranded. Here at Full Circle Auto Service in Lebanon, IL, our team of licensed auto repair experts can quickly pinpoint what triggered your check engine light and provide you with a clear, up-front quote. We’ve been providing area drivers with trusted all-makes auto service for over 25 years, and we’re proud to be a veteran and family-owned independent business.