The check engine light does not always signal a problem with your engine. However, you do not want to ignore a check engine light, as delaying repairs can cause more damage to your car. Additionally, a car will not pass an emissions test if the check engine light is on.
What Is a Check Engine Light?
A check engine light is part of your car’s onboard diagnostics system, which measures variables including engine speed, ignition timing, and fuel mixture. When a problem occurs in one of these systems, the car’s internal computer turns on a warning indicator labeled “check engine” or “service engine soon.” In some cars, a simple icon of an engine appears.
In addition to turning on the warning light, the computer stores a “trouble code” in its memory. This code identifies the source of the problem, which might be a malfunctioning sensor or a misfiring engine. Most auto repair shops have an electronic scan tool or diagnostic computer to read this code. Increasingly, consumers can find code readers they can use themselves at home.
The stored code gives some general information about the problem, but most people need a mechanic to fully diagnose and repair the issue.
In addition to turning on the light—known as the International Check Engine Symbol—the computer stores a “trouble code” in its memory that identifies the source of the problem, such as a malfunctioning sensor or a misfiring engine. The code can be read with an electronic scan tool or a diagnostic computer—standard equipment in auto repair shops. There are also a number of relatively inexpensive code readers that are designed for do-it-yourselfers.
The code will typically just point you in the direction of the problem, and still requires an experienced professional to fully diagnose and repair the issue. With the cost of a shop performing a diagnosis costing around $90, many car owners are turning to the Internet to find the cause and remedy. This can work in some instances, but when in doubt, seek professional help.
What to Do When the Check Engine Light Comes On
Many late-model cars have several versions of a check engine light. A blinking or red light typically indicates an urgent problem that needs immediate attention from a mechanic. For example, a blinking light might mean the engine is misfiring and releasing unburned fuel into the exhaust system.
Alternately, a steady light indicates a non-emergency problem. Make an appointment with a mechanic, and be aware that the car’s performance or fuel mileage might suffer as the car works to compensate for the problem.
If your check engine light comes on while you’re driving, don’t panic. First, check your other dashboard gauges to see if the car is overheating or low on oil pressure, as these problems require immediate attention. If you experience problems with performance such as reduced speed or loss of power, pull over as soon as safely possible, schedule a service appointment, and avoid driving to prevent any further damage to your vehicle.
Common Causes
- Gas Cap—A faulty or loose gas cap is one of the most common causes why the check engine light comes on, so check here first. The gas tank has valves to recirculate gasoline vapors to keep them from escaping. A loose gas cap prevents this circulation, triggering the check engine light. Even after you tighten the cap, the light might take a few trips to go off.
- Catalytic Converter—The catalytic converter changes carbon monoxide into carbon dioxide, protecting the environment from unsafe gases. When it is not functioning properly, the car can produce harmful emissions and negatively impact the car’s performance. Replacing the catalytic converter might not solve the problem, as the failure might result from a separate issue. A mechanic can help pinpoint and fix the underlying problem.
- Spark Plugs—The check engine light may signal a problem with the spark plugs, which ignite a mixture of air and fuel, creating combustion to power an engine’s cylinders. A malfunctioning spark plug can cause an engine misfire, increasing carbon emissions and affecting performance. Further, when one spark plug goes out, the others often follow.
- O2 Sensor. A car’s oxygen sensor measures how much unburnt oxygen remains in the exhaust system, then sends this information to a computer that regulates the mix of air and fuel entering the cylinders. A malfunctioning O2 sensor may cause the car to burn more fuel than it should.
- Mass air flow sensor (MAF). This measures the amount of air entering the engine. Because it is sensitive to oil, dirt, and water vapor, cleaning the MAF can sometimes solve the problem. In other cases, the sensor needs to be replaced.
Risks of Ignoring the Check Engine Light
If there is not apparent problem with the vehicle’s performance, you may be tempted to ignore the check engine light. However, this often exacerbates the problem and makes repairs more expensive. Additionally, neglecting the reason why the light came on may eventually impact the car’s transmission or engine, causing long-term damage that insurance may not cover. Tending to a check engine light promptly will keep your car operating at peak performance and will likely save you money in the long run.