Automakers and safety regulators could take months to nail down why air bag inflators made by Takata Corp. are exploding with too much force, meaning consumers cannot be certain replacement inflators installed under a sweeping recall are safe, industry officials involved in the process said.

Takata, 11 automakers that used its air bag technology and U.S. safety regulators are pursuing separate efforts to determine the root cause of problems linked to at least six deaths.

Replacement inflators that are currently being installed could eventually need to be replaced if it turns out that the real problem was not addressed before Takata began making parts to fix about 34 million vehicles covered by the expanded U.S. recall announced last week, several industry officials familiar with the probes said. The air bags can explode with too much force, causing shrapnel to fly out and hit drivers and passengers.