The Takata debacle continues, just weeks after the massive airbag recall was expanded to cover 34 million vehicles. Takata has already replaced 4 million potentially defective inflators, but now admits that 400,000 of those replacement parts may themselves be faulty and in need of replacement.

According to Reuters, sources at both Takata and the National Highway Transportation Safety Administration (NHTSA) confirm that at least 400,000 replacement parts still use a possibly harmful propellant. "Those will have to be replaced again," the Takata source told Reuters.

About 500,000 additional replacement parts, all manufactured for Takata by a variety of independent supplier companies, are currently regarded as safe. That leaves more than 3 million replacement parts that neither Takata nor NHTSA can confirm need to be replaced a second time.

Automakers have responded by expanding earlier recalls, with 3.3 million vehicles added to the recall list since news broke of the 4 million potentially faulty replacements. Honda, however, told Reuters that it has replaced 1.2 million driver-side airbags since September 12. All of these Takata-made replacements apparently use a different design, and will not need to be recalled again.

In February, NHTSA started to fine the company $14,000 for every day it didn't fully cooperate with the investigation into the crisis.

By the end of the year, Takata says that it hopes to be churning out at least 1 million replacements parts per month, about 70 percent of which will be made by outside suppliers. Clearly Takata is unable to handle the scale of the recall it faces, especially when replacement parts themselves subject to the same risks as the originals.

The U.S. House committee met on June 2 to determine what led to the massive recall and how NHTSA has handled the investigation.