5 common car problems and what they cost to fix

DETROIT — Drivers get nervous whenever the “check engine” light illuminates on their dashboard. It can signal anything from a missing $3 gas cap to repairs costing thousands of dollars.

But think of the light as a way to stay on top of problems and extend the life of a car. Often, it's warning about problems that can be avoided by keeping up with regular maintenance, says CarMD, a maker of vehicle diagnostic equipment.

While maintenance is expensive, it's crucial as people hang on to their cars longer. According to R.L. Polk, an automotive data firm, the average vehicle on the road is now 10.6 years old, up from 8.8 years a decade ago.

Here are the five most common reasons your “check engine” light might come on, and what you can expect to pay for the repair, including labor, according to CarMD:

1. Faulty oxygen sensor

The sensor measures the amount of unburned oxygen in the exhaust and tells the car's computer how much fuel is in the tank. If a faulty one is not repaired, the car's gas mileage could drop, since the sensor is sending incorrect information to the car. It costs less than $200 to repair.

2. Loose or missing gas cap

Technicians will often tighten the gas cap for free, or replace it for a few dollars. If it's not replaced, gas will evaporate from the car and decrease its gas mileage.

3. Broken catalytic converter

This one isn't good news, since it can cost up to $2,000 to replace. The catalytic converter uses a catalyst — most often a precious metal such as platinum — to convert harmful gases left over from combustion to less harmful emissions. CarMD says catalytic converters generally won't fail unless a related part, such as a spark plug, malfunctions, so it's wise to keep up with the car's maintenance schedule.

4. Malfunctioning mass air flow sensor

This sensor measures the amount of air supplied to the engine, which determines how much fuel should be delivered. When it malfunctions, it can result in a loss of power to the car, surges during acceleration and a decrease in fuel economy. It costs around $375 to fix.

5. Misfiring spark plugs

Spark plugs are small but essential, since they make the car go by igniting the compressed fuel in an internal combustion engine. Misfiring spark plugs can affect engine power and fuel economy and can also damage the catalytic converter. You can replace spark plugs yourself for around $10 or pay $300 for a technician to do it.

CarMD says the total average repair cost in the U.S. is $305.56, including $202.28 for parts and $103.27 for labor.

The most expensive cars to repair? Hybrids. They remain rare enough that their parts are pricier and fewer technicians are trained to fix them.

The report is based on data from 170,000 vehicle repairs made between 1996 and 2010. The data came from vehicle owners and technicians who downloaded information to CarMD.