WASHINGTON, D.C. --- The National Highway Traffic Safety Administration said it has upgraded its investigation of Chrysler's Jeep Liberty, following 22 customer complaints about the upper ball joint separating on either of the front wheels, the Associated Press reported. The problem has reportedly led to some instances of the front wheel collapsing.

The investigation involves more than 300,000 2002 and 2003 model year Liberty 4x4 SUVs.

Chrysler spokesman Max Gates told the Associated Press that the automaker has received 74 complaints and was continuing its own investigation. The company has not, however, received any reports of accidents or injuries linked to the problem, he said.

The NHTSA said that most of the complaints alleged that the joints separated at speeds of under 20 miles per hour. However, five complaints alleged that the separations occurred at speeds of 40 mph or more.

The NHTSA's investigation will include an engineering analysis to "assess the scope, frequency and safety consequences of the alleged defect," the agency said.

In August 2006, Chrysler recalled more than 800,000 2002-2006 Liberty SUVs to repair the front suspension lower ball joint. In November 2003, Chrysler recalled more than 300,000 2002-2003 Liberty vehicles because of problems with the lower ball joint, but some of the parts were actually damaged during shipping or installation, AP reported.