NEW YORK (CNNMoney.com) -- General Motors Corp., struggling to stem continued market-share losses and lift the perception of poor quality, on Wednesday announced a 100,000-mile, five-year powertrain warranty.

GM's new warranty, which will be offered on all GM passenger vehicles, will cover all powertrain components, meaning the engine and transmission, for five years or 100,000 miles. The warranty will apply to all 2007 model-year GM vehicles from all of the companies' brands.

"We're putting our money where our mouth is," said GM chairman and CEO Rick Wagoner at a press conference outside the company's Detroit headquarters.

The company is also expanding its roadside assistance and courtesy vehicle programs, he said.

The company has suffered from customer perception of producing lesser-quality cars than many import brands, particularly from Japan, even as some measures have shown that the quality gap has been closing.

The latest J.D. Power "dependability study," which surveyed 48,000 owners of 2003 model-year vehicles, ranked two GM brands, Buick and Cadillac, No. 3 and 4, respectively - ahead of Toyota, Honda and BMW. Lexus, the luxury brand of Toyota Motor, finished No. 1.

GM's vehicle quality has improved 25 percent over the past five years, according to the company's own measures, Wagoner said. Repairs covered under warranty have been reduced 40 percent during the same period, he said.

The magazine Consumer Reports still regards GM quality as questionable, however. In a recent test of luxury sports cars, the Chevrolet Corvette Z06 was "not recommended" in spite of performance and comfort that were virtually identical to the more expensive Porsche 911. That was because of poor "predicted reliability," which the magazine gauges from owner survey data.

The lower perceived quality has caused GM (Charts) to offer larger cash-back offers or other costly incentives to hang onto declining market share. But offering a longer warranty will also cost the company money as it struggles to trim losses from its core North American auto operations.

The terms of the warranty we set to be longer than most new vehicle buyers keep or drive their cars and trucks, said Mark LaNeve, GM's vice president for sales and marketing.

"We want to get the quality issue off the table as it pertains to our eight brands," said LaNeve.

While the warranty is not "bumper to bumper," meaning it does not cover every component of the vehicle, it was designed to alleviate worries about problems with the vehicle's most critical and expensive components, LaNeve said.

Unlike some other automaker warranties, GM's is transferable to a different owner, LaNeve said. That is a point that should help boost the value of GM vehicles in the used car market. That has been a goal for GM because it means buyers will recover more of their investment in the car when the time comes to sell or trade it in. GM vehicles have suffered from poor residual value.

Buyers who have already purchased one of GM's 2007 model-year large SUVs will get a letter in the mail telling them that their warranty has been extended, LaNeve said.

GM currently offers a 36-month, 36,000-mile warranty on most of its vehicles.

Some Korean automakers such as Hyundai, which has also faced consumer perception problems, offer a five-year, 60,000-mile warranty on just about all parts of their vehicles, along with a 10-year, 100,000-mile warranty on the powertrain.

DaimlerChrysler's Chrysler Group, which is made up of the Dodge, Jeep and Chrysler brands, used to offer a seven-year, 70,000-mile warranty but dropped that offer with the 2006 model year, citing a lack of consumer interest.

The new warranty plan will be advertised in a 60-second TV spot that will be shown during Thursday night's football opener on NBC. The TV spot shows cars, both GM and non-GM vehicles, stuck in gridlocked traffic. The GM vehicles begin, one by one, to rise into the air, where they then fly above the traffic.

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