Chrysler Group LLC will start repairs on about 371,000 vehicles equipped with potentially defective Takata Corp. air bag inflators in December, nearly six months after it said it would comply with a request by U.S. safety regulators to make fixes, reported The WSJ.

The company, in a letter to the National Highway Safety Traffic Administration dated Nov. 5, also said it had tested in September several Takata-made inflators salvaged from affected models in Florida and concluded they were working properly.

Chrysler, a unit of Fiat Chrysler Automobiles NV, said it is taking the issue “very seriously” but noted numerous times in its letter that “no defect determination has been made” in the population of vehicles NHTSA is investigating. It has maintained that its field action is “not a safety recall.”

The letter, provided to The Wall Street Journal by NHTSA, contained Chrysler’s response to questions posed by the agency on Oct. 29 about a potential defect involving Takata air bags kept for prolong periods in hot, humid climates. Nine other auto makers also received letters requesting information, including Honda Motor Co. , Toyota Motor Corp. and BMW AG . The responses have yet to be posted to NTHSA’s website.

U.S. safety regulators say they are aware of six incidents in which the air bag has exploded with too much force during a collision, spraying the driver and occupants with metal fragments.

All the incidents occurred in high-humidity states and U.S. territories and one involves a 2006 Dodge Charger in southern Florida in which the driver was injured.

However, NHTSA and Takata haven’t been able to pinpoint an exact defect, leaving auto makers to decide for themselves what to do with the suspected air bags. Some are formally recalling the vehicles, while others are replacing the inflators through so-called regional service or field actions, which have less regulatory scrutiny.

Chrysler now plans to launch its field action Dec. 19 to replace Takata air bag inflators in vehicles residing in Florida, Hawaii, Puerto Rico and the Virgin Islands. In June, it said it would swap out the inflators at NHTSA’s request but hasn’t had parts available to make the fixes.

The company, in its letter, said it had investigated getting replacement parts from other suppliers but concluded it would take too long. It now plans to use newer Takata inflators in the repairs.

The auto maker says it has identified more than 10,000 air bag deployments on Chrysler vehicles in the U.S. equipped with the suspected inflators. Of those, it is only aware of the one air bag rupture incident on the Dodge Charger.

The company’s letter follows Honda Motor’s announcement last week that it would upgrade its so-called “regional safety campaign” to a formal recall, after testing found that air bags kept in high-humidity areas resulted in abnormal deployments.

Honda’s recall limits repairs to 13 high-humidity states and U.S. territories—specifically, Alabama, Florida, Georgia, Hawaii, Louisiana, Mississippi, South Carolina, Texas, Puerto Rico, U.S. Virgin Islands, Saipan, Guam, and American Samoa. The specific number of vehicles is undetermined at this point, the company said.

Chrysler, in its letter, says there are two distinct populations of air bag inflators as defined by Takata—one that the supplier has determined to have a defect and another group still under investigation.

The company says the inflators on its models belong to the latter group, which includes air bag inflators on the driver’s side produced between Jan. 1, 2004, and June 30, 2007, and passenger side air bags made between June 1, 2000, and July 31, 2004, it said.

Chrysler estimates that about 37.8 million vehicles world-wide could be equipped with what it calls the “beta” type of inflators.

In its testing, Chrysler worked with Tataka engineers to analyze 18 drivers’ side air bag inflators obtained from Florida salvage yards and one from Chrysler’s tech lab. While they did find some traces of elevated moisture, they concluded that the air bags “would have deployed as designed in the field.”