An annual survey undertaken by JD Power of vehicle owners to determine vehicle dependability has found that increased engine and transmission problems have contributed to a decline in overall vehicle dependability for the first time in more than 15 years.

JD Power said that owners of three-year-old vehicles (2011 model year) reported more problems than owners of three-year-old vehicles last year, according to the JD Power 2014 US Vehicle Dependability Study.

The study, now in its 25th year, examined problems experienced during the past 12 months by original owners of 2011 model-year vehicles. Overall dependability is determined by the number of problems experienced per 100 vehicles (PP100), with a lower score reflecting higher quality.

The study found that overall vehicle dependability averages 133 PP100, a 6% increase in problems from 126 PP100 in 2013. This marks the first time since the 1998 study that the average number of problems has increased.

"Until this year, we have seen a continuous improvement in vehicle dependability," said David Sargent, vice president of global automotive at JD Power. "However, some of the changes that automakers implemented for the 2011 model year have led to a noticeable increase in problems reported."

Engine and transmission problems increase by nearly 6 PP100 year over year, accounting for the majority of the overall 7 PP100 increase in reported problems. JD Power said that the decline in quality is particularly acute for vehicles with 4-cylinder engines, where problem levels increase by nearly 10 PP100. These smaller engines, as well as large diesel engines, tend to be more problematic than 5- and 6-cylinder engines, for which owners report fewer problems, on average.

"Automakers are continually looking for ways to improve fuel economy, which is a primary purchase motivator for many consumers, particularly those buying smaller vehicles," said Sargent. "However, while striving to reduce fuel consumption, automakers must be careful not to compromise quality. Increases in such problems as engine hesitation, rough transmission shifts and lack of power indicate that this is a continuing challenge."