Honda Motor was so worried with mounting recalls for Takata air bags that it purchased used and scrapped cars in Japan to conduct its own tests.

Nearly 21 million vehicles have been recalled by automakers since 2008 for defective Takata inflators. Honda has recalled 14 million cars, mainly in the U.S., where four of the five deaths have taken place. The fifth was in Malaysia.

Two senior Honda insiders spoke to Reuters and said the tests on 100 to 150 Takata air bags at Honda's quality center near Utsunomiya, north of Tokyo, during the first half of the year indicated shortcoming in Takata's manufacturing quality and casted doubt on the competence of a company that Honda considered part of its core group of suppliers.

"We doubted if Takata was producing air bags to the specifications we had mutually agreed on," one of the insiders said, who asked not to be named. "When we did not receive a clear analysis of what was happening, we decided to conduct our own tests and we found the quality of those inflators to be all over the map in term of key quality metrics."

Takata has denied Honda tested used air bags because over being dissatisfied with Takata's explanations, adding that it had not been told of any quality issues found by the automaker.

"If Honda did the kind of quality tests on Takata inflators you're describing, wouldn't you assume Honda would communicate with us, to ask us about the quality lapses they supposedly found? As far as we know, and we looked into it extensively, there has been no such communication between us," said a Takata spokesman recently.

The Honda insiders said that tests didn't identify the cause of the defect but caused the company to believe that manufacturing issues could have played a key role.

"What's most important to us is our customer, and to take necessary action as quickly as possible for their safety ... and remove fears and worries felt by the customer as part of the air bag recalls," Honda's chief spokesman Kaoru Tanaka said, according to Reuters.

The spokesman confirmed that the company conducts component quality tests at times when defects are suspect, but doesn't release results or comment on tests.

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