WASHINGTON — U.S. Transportation Secretary Anthony Foxx told senators on Thursday that federal regulators didn’t take earlier action regarding a potentially defective ignition switch in certain General Motors Co. cars because data from crash investigations was deemed “inconclusive.”

Foxx, who went before a Senate Appropriations subcommittee, was questioned on why his agency’s National Highway Traffic Safety Administration waited until late last month to open an investigation on why GM took so long to initiate a recall of 1.6 million cars.

“Over the last decade, there were complaints related to (these) particular vehicle(s),” he said, “and despite three crash investigations and other research, the data was inconclusive. It just didn’t point to a formal investigation.”

GM is recalling 2005-2007 Chevrolet Cobalts, 2003-2007 Saturn Ions and several other models because of concerns over an ignition switch that can be inadvertently jostled into a position where a vehicle’s power steering is disabled and air bags will not deploy.

Twelve deaths and 31 crashes have been linked to the defective switches.

But congressional investigators want to know both why GM didn’t act sooner – given reports that it should have or could have known about potential problems based on hundreds of complaints for years – and why NHTSA didn’t force the automaker to act.

“Is there a number of complaints or injuries that trigger NHTSA to investigate?” asked Sen. Susan Collins, R-Maine, who followed up on questions first raised by the Transportation Subcommittee’s chair, Sen. Patty Murray, D-Wash. Foxx – who has only been on the job since last July – said the decision to investigate “depends on the exact circumstances of the situation.”

A Senate subcommittee of the Commerce, Science and Transportation Committee is expected to take up the issue. The House Energy and Commerce Committee, chaired by U.S. Rep. Fred Upton, R-Mich., is promising a full investigation and has asked GM and NHTSA to submit documents by March 25.

As detailed in a Detroit Free Press report, GM submissions to NHTSA make clear that while it had been tracking issues associated with the ignition switches since 2007, a review of records done last month showed much earlier indications of a potential problem.

As far back as 2001, issues related to the ignition were identified in pre-production of the Ion. In 2003, a service technician noted a vehicle stalled while being driven and that the weight of keys on a key chain had “worn out the ignition switch.”

GM is telling drivers to remove any additional weight from key chains until the switch can be replaced by dealers.

As noted by Foxx, NHTSA initiated three outside investigations into crashes involving the now-recalled vehicles in 2004, 2005 and 2006. In two of those crashes where air bags did not deploy, onboard computers noted the ignition switch had been moved from “run” to “accessory” – potentially disabling the air bags. Three people died in those two crashes.

That fact alone, however, may be misleading. Only one of the reports prominently mentions “power loss due to the movement of the ignition switch” as a possible cause for the air bags not deploying. NHTSA also has a list of 830 special crash investigations in which air bags did not deploy. There are many potential reasons for those crashes.