Drivers in the western U.S. paid 13% more for repairs than Midwest; 11% more than Southeast and 5% more than Northeastern consumers... and Arizona drivers paid the highest price in the country, according to CarMD Corporation, a Fountain Valley, CA business for vehicle diagnostics and maintenance.

CarMD recently produced data analyzing 80,000 repairs nationwide made on vehicles with "check engine" light problems in 2010. Working with a network of Automotive Service Excellence (ASE) certified technicians, CarMD compared costs and ranked repairs, state-by-state.

CarMD's "Vehicle Health Index" reports that the average cost of U.S. "check engine"-related repairs in 2010 was $356.04, including $212.44 for parts and $143.61 for labor.

Arizona has the dubious distinction of having the highest average cost in the nation. Its average cost of $421.49 is 18% greater than the national average; parts ($260.29) averaged 23% higher than the national average; and labor ($161.20) was 12% higher than the U.S. average.

"We are releasing this data to empower consumers and technicians with a better understanding of common repairs and costs, and, to call attention to the fact that, regardless of region, drivers who follow a regularly scheduled maintenance program and address small problems early tend to have reduced fuel bills and repair costs," says CarMD's Art Jacobsen. "That said, if you live in a state with harsh weather conditions such as Arizona's heat or North Dakota's cold, it's imperative to take care of your car to avoid ctastrophic vehicle failures."

The states with lower repair costs had more gas-cap related problems. A loose gas cap, which is one of the most common causes for check-engine problems, accounted for nearly 12% of repairs in D.C. and 11% in Ohio, (two areas with the lowest average repair costs). While loose, damaged or missing gas caps are an inexpensive fix, they cause 147 million gallons of gas to evaporate annually.

The number-one most common repair in 2010 was for "oxygen sensor replacement." O2 sensors monitor the amount of unburned oxygen in the exhaust and tell the car's computer how much fuel to inject for proper operation. If a faulty O2 sensor is not repaired the car's fuel economy will drop dramatically. The average cost to repair an 02 sensor is $238.71 including parts and labor, but failing to do so can lead to as much as a 40% reduction in your gas mileage.

After Arizona, the states with the highest average repair costs are New Mexico, Colorado, California and Nevada. Who's the lowest? D.C., Missouri, Ohio, Wisconsin, Nebraska and Mssissippi.

For the complete state-by-state ranking please click on