(May 23, 2011) FOUNTAIN VALLEY, Calif. (PRNewswire) — As vacationers pack up their cars, trucks and SUVs to embark on weekend getaways and summer road trips, national gas prices and average vehicle age are reaching all-time highs. 

A study by CarMD.com Corporation, a provider of consumer automotive diagnostic products and information, also finds that 64 percent of U.S. vehicle owners have put off automotive maintenance, increasing the risk of vehicle problems. 

In response, CarMD reveals the top five most frequent car repairs that, if ignored, can significantly reduce gas mileage and lead to roadside breakdowns, along with tips to help motorists avoid becoming a tow truck company statistic this summer.   

• Replace oxygen sensor — The number one reason for the dreaded "check engine" light last year was a faulty oxygen sensor (02), which monitors the amount of unburned oxygen in the exhaust and tells your car's computer when there is too much (or not enough) fuel. 

A faulty O2 sensor can reduce gas mileage by up to 40 percent.  During a 500-mile road trip, an unrepaired O2 sensor can cost you an extra $50 at the pump. Your car may be running just fine but the meter at the pump will be running even faster. 

If you drive an older car with high mileage chances are you'll need to replace an O2 sensor or two as part of the normal aging process.  O2 sensors don't cost very much (usually about $20) and with today's gas prices they will pay for themselves very quickly 
   
• Check gas cap — A loose, faulty or cracked gas cap is the second most common "check engine" light culprit, accounting for more than 9 percent of repairs in CarMD's automotive repair database. 

If left ignored, a faulty gas cap may reduce your fuel economy by a couple miles per gallon. Loose, cracked and missing gas caps cause an estimated 147 million gallons of expensive fuel to evaporate each year. The good news is this is an inexpensive problem to repair, even during a road trip. 

The best way to avoid gas cap problems altogether is to tighten the cap after every fill-up or consider a locked gas cap.
   
• Replace catalytic converter — The third most common repair is to "replace the catalytic converter," but it really shouldn't even be in the top 10 most frequent repairs. A catalytic converter normally won't fail unless a smaller faulty part, such as a spark plug or O2 sensor, is ignored for too long. 

A failed catalytic converter can cost as much as $2,000 to repair and will quickly cause severe damage to your car, as indicated by a blinking check engine light. If you ever see a blinking check engine light on your dash, pull over immediately, stop driving and have the vehicle towed to a repair shop.  Paying attention to your car's warning signs and fixing little problems early can help you avoid expensive catalytic converter repairs, among others.
   
• Replace mass air flow sensor — The 4th most common repair is "replace mass air flow (MAF) sensor," which measures the amount of air supplied to your car's engine and determines how much fuel to deliver into the engine. When malfunctioning, it can result in a lack of power, engine hesitation or surge upon acceleration. 

If left unfixed, a bad mass air flow sensor can also lower your fuel economy by 10 to 25 percent. It is particularly susceptible to dry, dusty summer road conditions. An easy and affordable way to keep your mass air flow sensor healthy is by keeping your car's air filer clean. Air filters usually cost less than $20 to replace, while mass air flow sensors run about $300 in parts and labor.

• Replace spark plug — The fifth most common car repair last year was "replace spark plug or spark plug wire." The small but mighty spark plug is responsible for igniting a car's air/fuel ratio and can cause big problems when it fails. 

At a minimum, a faulty spark plug will reduce gas mileage by about 10 to 20 percent, but more concerning is its potential to cause a misfire that can melt and permanently damage your car's catalytic converter(s). Spark plugs usually need to be replaced every 30,000 to 40,000 miles, but can fail earlier if you have a lot of oil or dirt build up in your engine. 

If you do it yourself, replacing a spark plug can cost under $10. Having it done by certified mechanic costs a couple hundred dollars or so, but can save thousands.

All of the problems listed above are tied to your car's computerized diagnostic system, which is designed to alert you to large and small problems through your vehicle's "check engine" light. 

This technology is standard on all vehicles manufactured since 1996.  CarMD's network of automotive service excellence-certified technicians has been compiling a database to track vehicle failures, repairs and related costs for the past 14 years, and is sharing this information to help educate motorists. 

The best way to avoid these and other car problems and breakdowns is to follow a regularly scheduled maintenance program that includes regular fluid changes, proper tire inspection and maintenance, and quick attention to all warning lights.