A preliminary investigation is the first step in a process that could lead to a recall if regulators determine that a safety issue needs to be addressed by a manufacturer.

The National Highway Traffic Safety Administration said its probe into an estimated 440,000 Nissan Altima cars from the 2007 and 2008 model years concerned a possible leak in the brake master cylinder that could reduce the effectiveness of the brakes.

NHTSA said it had received 20 complaints from Altima drivers. Of these, two alleged a reduction in brake effectiveness while 18 reported only illumination of the brake warning light.

The agency said it was also investigating Chrysler's Jeep Wrangler from the 2007 and 2008 model years, potentially affecting 222,500 vehicles, over airbag light illumination indicating an airbag clockspring failure.

A clockspring is a coil under the steering wheel that maintains an electrical connection to the airbag on the driver's side. A broken circuit can mean the airbag will not inflate.

NHTSA said it had received 29 consumer complaints from Jeep drivers. Of these, 23 identified the clockspring wiring assembly as the source of the issue, while the other six only said the airbag light had been illuminated.

Of 14 owners contacted, six said they owned right-hand-drive versions typically used by postal carriers.

A third probe involves GM's 2007 Saturn Aura, potentially affecting 65,105 cars, over a transmission shift cable that could fail, causing the park gear not to fully engage.

The agency said it had received eight complaints alleging that the transmission shift cable had failed, causing the vehicle to roll away, move or accelerate with the shifter in park, or to accelerate in the opposite direction than the driver intended.

NHTSA did not disclose any crashes or injuries in connection with any of the reported problems.

Spokesmen for the three companies said the carmakers were cooperating fully with the investigations.