CarMD, which sells automobile diagnostic systems, analyzed more than 160,000 repair bills given to drivers in 2011 who pulled into auto shops because the "check engine" light came on.
The average nationwide cost of repairs in that situation was $334 in 2011, down 6% from 2010, primarily because of a drop in labor costs, the study found.
But the average cost of those repairs were higher in Wyoming ($389), Utah ($379), California ($368), Montana ($364) and Arizona ($363), according to the study.
Why? The study did not reach a conclusion, but CarMD officials said drivers far from their local repair shops can be at the mercy of unscrupulous mechanics.
Also, road trips can put extra wear and tear on a car, resulting in more serious automotive problems, said Kristin Brocoff, a spokeswoman for CarMD.com. "You can look at so many facets of this study and draw your own conclusions," she said.
The lowest average repair costs were charged in Indiana ($284), Maine ($290) and Wisconsin ($290), the study found.