Signs that a car engine is malfunctioning include decreased fuel economy, reduced acceleration, operation at a higher temperature and, ultimately, failure to operate. On the dashboard, the "Check Engine" light shows the owner that the engine has a serious problem requiring immediate attention from a mechanic.
When the "Check Engine" light comes on, the source is generally a problem in one of five areas: the oxygen sensor, the gas cap, the mass airflow sensor, the spark plugs or plug wires, and the catalytic converter. The gas cap is the easiest to fix, as the only requirement is to ensure that the gas cap is tightly screwed onto the tank. After restarting the engine, the light should no longer activate if the gas cap was the problem.
A faulty oxygen sensor causes the engine to burn more gas than it needs to, and this can eat up as much as 40 percent of the car's mileage, as well as damage the spark plugs and catalytic converter. The mass airflow sensor measures the air coming into the engine to determine the necessary amount of fuel. Faulty sensors often damage oxygen sensors, spark plugs or the catalytic converter, and both performance and mileage suffer. If the spark plugs or plug wires are faulty, the car's performance suffers, and clogs sometimes develop inside the catalytic converter. A faulty catalytic converter does not deal with toxins appropriately, and the car fails emissions tests and runs at a higher temperature.