CarMD.com released the most common reasons for your check engine light coming on. Car MD is a diagnostic tool that plugs into your car to give you a readout of issues it finds. I’ve had one of their code readers for many years. Here is the culmination of their research.
The no. 1 most common fix is “replace Oxygen Sensor.” The O2 sensor monitors the amount of unburned oxygen in the exhaust and tells your car’s computer when there is either too much, or not enough fuel. So what’s it mean to you? A faulty O2 sensor costs less than $200 to fix but can lead to as much as a 40 percent reduction in gas mileage if ignored.
The no. 2 most common repair is “replace loose, damaged or missing gas cap.” Simply tightening the cap for free or replacing it for a couple dollars is the fix, but if left unchecked can result in a 0.5% decrease in gas mileage and harm the environment.
“Replace catalytic converter(s)” is now the no. 3 most common car repair, but it shouldn’t even be in the top 10. A catalytic converter usually won’t fail unless a related part – such as a faulty spark plug – is ignored for too long. This is a great example of why it’s so important to address small problems early. A damaged catalytic converter will cost $1,000 or more to fix.
The no. 4 most common repair is “replace the Mass Air Flow Sensor.” The MAF sensor is responsible for calculating the air coming into your car and determining how much fuel to shoot into the engine. When malfunctioning, it can lower MPG by 10 to 25%. It costs about $375 to fix, but is vital to saving dollars at the pump.
The small but mighty spark plug is no. 5. Responsible for igniting a car’s air/fuel ratio, spark plugs are essential. When they fail, they can cause a “misfire,” reduce gas mileage, and ultimately melt/ruin your catalytic converter. If you do it yourself, replacing a spark plug can cost under $10. Having it done by certified mechanic costs a couple hundred dollars, but can save you thousands.