DETROIT (Reuters) -- General Motors Co. conducted an additional 16 tests on cars with the defective ignition switch linked to at least 13 deaths to further support its position that the vehicles are safe to drive with only the key in the ignition, according to a document posted online by U.S. safety regulators.
The No. 1 U.S. automaker said it removed parts from the faulty switch to make it easier for a single key to move out of the "run" position, but the switch did not malfunction in the additional tests, which were completed after a similar round in March, according to a GM report filed by the U.S. National Highway Traffic Safety Administration.
"Test results showed no incidents of unintended key rotation when only an empty key ring was attached to the ignition key," the company said in the report, which was dated May 6.
GM has recalled 2.6 million cars, including Chevrolet Cobalts and Saturn Ions, because the defective ignition switches are prone to being jostled into accessory mode while the cars are moving. That would shut off engines and disable power steering, power brakes and air bags.
Safety advocates, plaintiffs' attorneys and U.S. lawmakers have said the cars were not safe, even when driven with only the vehicle key on the key ring, and had called for GM to tell drivers to stop operating their cars until they could be repaired.
In the newest 16 tests, GM removed the switch detent plunger and spring, making it easier for the switch to change positions, according to the NHTSA filing.
"We stress tested our conclusions from the initial 80 tests," GM spokesman Jim Cain said. "We did this at our own discretion to present the strongest possible case that our advice is good."
None of the new tests included scenarios where the driver's knee intentionally bumped the ignition switch. Cain said that during all of the 100-plus tests the drivers' knees never hit the switch by accident.
GM executives have maintained that the recalled cars are safe to drive before the bad switch is replaced as long as drivers use only the vehicle key. The automaker repeated that stance in an April 2 response in a Texas lawsuit, where the plaintiffs had asked the judge to compel the Detroit company to have consumers park the cars until they were repaired.
Both the judge and later NHTSA said GM's testing showed the parking of the cars was unnecessary.
GM conducted more than 100 tests in total from Feb. 24 through April 3, according to the NHTSA filing. GM previously said it had conducted more than 80 tests on rough roads and in simulated panicked stops that were meant to replicate how the ignition switch performed with only the key in it.