Continental and some automakers knew of problems with airbag control units for years before the first recalls were ordered last fall, according to documents released by U.S. regulators.

The following is a timeline provided by the U.S. safety regulator National Highway Traffic Safety Administration on Thursday when it also announced a recall of 5 million U.S. vehicles with air bag control units supplied by Continental Automotive systems, a unit of Continental AG (>> Continental AG).

-- Jan. 30, 2008: Continental receives an air bag control unit removed from a Daimler AG (>> Daimler AG) Mercedes-Benz vehicle in which an air bag warning light was illuminated. Continental determines that a power supply module malfunctioned and sent that model to its maker, Atmel Corp. (>> Atmel Corporation)

-- March 2008: Atmel finds the power supply to the air bag control module can be interrupted if corrosion occurs.

Atmel implemented countermeasures in March and April to reduce the likelihood of the corrosion. Atmel made a corrective action in May 2008 to prevent the corrosion from occurring in the future.

-- Early 2011: Continental learned of two inadvertent deployments of air bags, one in a Daimler vehicle and the other in a vehicle made by Fiat Chrysler.

-- August 2011: Continental determined that the inadvertent deployments from earlier in 2011 were related to corrosion of a power supply component in the air bag modules in the Fiat Chrysler and Daimler vehicles.

-- March 2013: Daimler started a service campaign, which is short of a recall, outside the United States to address the issue involved in the 2011 inadvertent deployment.

-- April 2015: American Honda, a unit of Honda Motor Co (>> Honda Motor Co Ltd), asked Continental do analyze an air bag control module in a 2008 Honda Accord involved in an Oct. 26, 2013 accident involved in a lawsuit.

-- July 21, 2015: Continental determined the power supply component in the air bag control module had malfunctioned. NHTSA on the same day asked Continental to analyze an air bag control module from a 2008 Honda Accord involved in a March 30, 2015 accident.

-- August 18, 2015: NHTSA opened an investigation regarding 2008 to 2010 model year Honda Accord sedans.

-- Sept. 9, 2015: Continental analyzed an air bag control module in the March 30 accident and took the same type of device from the Accord in the Oct. 26, 2013 crash. On Sept. 28, Atmel confirmed the power supply component had malfunctioned.

-- Oct. 27, 2015: Daimler's Mercedes-Benz recalled 126,000 vehicles from 2008 to 2010 model years.

-- Jan. 15, 2016: Honda told Continental that a safety-related defect exists in the air bag control modules of certain Accords from model years 2008 and 2009, saying it was the same defect covered in the October 2015 Mercedes-Benz recall.

(Reporting by Bernie Woodall in Detroit Editing by W Simon)

By Bernie Woodall