It has no doubt been a banner week for Hyundai Motors at the Detroit Auto Show, hauling in two big awards for "Car of The Year," and the brand with the highest customer loyalty. But it has its detractors too.

The Korean automaker stole headlines at Detroit's auto show when its compact Elantra garnered North American Car of the Year honors--beating out new models like Toyota Camry, VW Passat and Ford Focus--to the surprise of many attendees. Then, J.D. Power released a study that ranks Hyundai first in customer retention rates among 33 automotive brands.

But the awards have rekindled debate about whether Hyundai's fuel-efficiency claims on the newly popular 2011 Elantra model meet reality.

A number of disappointed customers and advocacy organization Consumer Watchdog have expressed concerns that the company's sticker estimates of 29 miles per gallon in the city and 40 mpg on the highway are grossly exaggerated.

"Neither Hyundai or any other car company should be allowed to misrepresent its efficiency standards or dupe consumers into buying its cars," wrote Jamie Court, president of Consumer Watchdog, in a letter last month to the Environmental Protection Agency that asks for the Elantra's fuel economy to be re-tested.

As gasoline prices have settled in at between $3.25 and $4.00 per gallon for regular, car companies have been doing everything they can to get their new cars to hit 40 mpg on the highway and to boast that fuel economy in advertising.

In a separate letter to the automaker, Consumer Watchdog demanded Hyundai remove its 40-mpg claims from its advertising campaigns, including upcoming Super Bowl commercials. The automaker stands behind its 40-mpg claim.

"We have no intention of removing our fuel economy numbers from our advertising," company spokesperson Jim Trainor said in a written response. "Simply put, the charges being made by Consumer Watchdog don't hold up."

Tests done by Consumers Union and Motor Trend recorded shortfalls from Elantra's 33-mpg combined claim by 12 and 29 percent, respectively. A recent USA Today review said that its drivers averaged 22 miles per gallon in city driving, significantly shorter than the 29-miles per gallon claim.

The Consumer Watchdog letter questioned whether the majority, if not all, of the company's self-testing took place in ECO mode mode, which modifies engine and transmission control resulting in up to 7 percent fuel savings, according to Hyundai.

In his letter to the EPA, Court cited a example of a California motorist who wrote on a message board that he was "hugely disappointed" in his 2011 Elantra because it averaged 18 or 19 miles per gallon in city driving because fuel economy drove his purchase. Rather than focus on a handful of web complaints, Hyundai said an independent JD Power survey found that Elantra owners were the happiest of any car in the compact segment when it came to fuel economy.

The EPA has not yet said whether it will investigate the complaint.