As early as 2003, Takata Corp ran an investigation into an air bag inflator that ruptured in a BMW vehicle, but concluded the problem was an anomaly, the company said on Tuesday, ahead of a second U.S. congressional hearing on dangerous air bags it supplied.

In addition, technicians employed by the Japanese auto parts supplier in Michigan tested inflators for potential defects in 2004, over a year before Takata has said it first learned of defects that are now linked to five deaths, two people directly involved in Takata's investigation told Reuters.

The disclosure that Takata was looking into problems with its air bag inflators earlier than previously disclosed could open the company to more intense scrutiny from U.S. lawmakers, regulators and prosecutors in an ongoing criminal investigation into a series of recalls that now targets more than 16 million vehicles worldwide.