Federal auto safety regulators are investigating 440,000 Nissan Altimas for braking issues.

The National Highway Traffic Safety Administration said today it had opened a preliminary investigation into 2007-08 Nissan Altima vehicles after receiving 20 complaints alleging brake master cylinder leakage, reported The Detroit News.

NHTSA had 16 of those complaints since October. Two complaints allege a reduction in brake effectiveness.

The rest said the only symptom of the problem was illumination of the brake warning lamp. Of the 18, 17 said a Nissan dealer diagnosed the problem as a leak in the brake master cylinder, including several that indicated brake fluid leaked into the brake booster assembly.

Nissan has also provided reports of master cylinder leakage in Early Warning Reporting system submissions.

In July 2008, Nissan recalled 169,000 2007-08 Nissan Sentra vehicles to address a defect in the brake master cylinder that could result in brake fluid slowly leaking from the master cylinder into the brake booster assembly.

In October 2009, Nissan expanded the scope of the Sentra recall by adding an additional 10,586 2008 vehicles.

Nissan said the recall of the Sentras was prompted by a gap in the internal seal groove in the body of some master cylinders.

The leakage resulted in reduced brake reservoir fill level, resulting in brake warning lamp illumination. Nissan said continued operation with the warning lamp illuminated for "a relatively long period of time" may result in loss of one braking circuit.

Nissan spokesman Colin Price said the company is working closely with NHTSA.

"Nissan is committed to customer safety and the quick, effective resolution of safety issues and will work closely with NHTSA to investigate this issue. While we are aware of several customer complaints made directly to NHTSA related to this issue, we are not aware of any accidents or injuries related to this investigation," Price said.