In June, General Motors learned from the National Highway Traffic Safety Administration that a Chevrolet Volt caught fire three weeks after a test crash.
Not until NHTSA did additional testing on Volt batteries in November did GM disclose the potential risk -- and tell owners, dealers and the public that it is critical to drain power from the battery pack immediately after a crash.
NHTSA, too, waited months to disclose possible fire hazards of the Volt. The agency crashed the Volt on May 12, and a fire on the vehicle broke out in June.
The agency first acknowledged the June fire on Nov. 11. And on Nov. 25, NHTSA announced it was opening a safety defect investigation to assess the Volt's battery-related fire risks.
The Volt's possible fire hazard has caused a public relations nightmare for a vehicle that GM touts heavily in its advertising. In 2009, when the company was hurtling toward bankruptcy, company execs used the Volt to underpin the case for a taxpayer-funded rescue.
GM said it would consider buying back Volts from customers concerned about the fires. In an interview last week with Reuters, CEO Dan Akerson said the company may redesign the Volt's battery.
The tendency of lithium ion batteries -- which are used in laptops and cell phones -- to overheat is widely known. And GM designed an elaborate sensing and liquid cooling system to regulate the temperature of the Volt's battery pack, a combination of 288 battery cells.
Joan Claybrook, a former NHTSA administrator, said, "Not to tell them anything for six months makes no sense to me. NHTSA could have put out a consumer alert and I think they should have done so."
She added, "I believe they delayed it because of the fragility of [Volt] sales."
In June, when NHTSA told GM about the Volt fire, GM engineers worked with NHTSA to identify the cause, said GM spokesman Rob Peterson.
As its engineers investigated, GM didn't feel it had anything to communicate to the public because it was one fire, occurring weeks after the crash, he said.
"It's kind of odd in many respects when a car has an event three weeks after the crash," Peterson said. "The question became: What was making this happen and what do we have to do?"
NHTSA said it is working on a standard for dealing with electric car batteries after a wreck. As of now, it's up to automakers to make such guidelines available to the public, NHTSA said.
NHTSA's side-impact test damaged the Volt's battery and ruptured the coolant line. Despite the fire, the agency gave the Volt a five-star crash test rating this summer. The rating covers a car's ability to prevent body injuries, and doesn't cover battery fires.
In July GM said it formalized a procedure to power down the battery. The car had been on sale for six months.
But it kept the procedure to itself as NHTSA, working with GM engineers, continued to crash-test the Volt in an effort to replicate the fire, but without success, GM said.
Not until November did further testing in the labs produce a fire. In three tests meant to simulate a side-impact collision, one battery began to smoke and emit sparks within hours after it was damaged; another caught fire in the testing facility.
On Nov. 25, NHTSA opened a formal safety investigation into the Volt. Last Monday, GM executives responded to the probe in a conference call with the media. The company also sent letters to thousands of dealers and Volt owners to reassure them that the car is safe.