GM probe
A man walks past a row of General Motors vehicles at a Chevrolet dealership on Woodward Avenue in Detroit, Michigan April 1, 2014. Reuters/Rebecca Cook

DETROIT/WASHINGTON (Reuters) - General Motors engineers reported accidentally turning off ignition switches in a Cadillac SRX with their knees more than eight years ago, and they ordered a similar fix to a similar problem in smaller, cheaper cars linked to 13 deaths, according to documents from parts maker Delphi Automotive.

The documents, provided to U.S. safety regulators, show GM used the same part, from the Cadillac Catera sedan, to make ignition switches more difficult to turn off on the 2007 Cadillac SRX crossover and the 2007 Saturn Ion and Chevrolet Cobalt sedans. Delphi supplied the GM-designed switches for all of those models.

The documents are the first indication that GM's luxury Cadillac brand experienced ignition-switch problems similar to those that triggered the recall earlier this year of 2.6 million GM compacts, including the Cobalt and Ion.

GM did not immediately respond to requests for clarification.

The Delphi documents, released on Wednesday by the U.S. National Highway Traffic Safety Administration, also may indicate that earlier versions of the Cadillac SRX, from model years 2004-2006, used a switch part from the 2003 Ion. One document says the SRX "in the beginning of the program" used switch parts from "Delta" vehicles, the code name for the GM small-car family that includes the Ion and Cobalt.

The original SRX ignition switch part also was used in the 2003-2007 Cadillac CTS sedan, according to online GM parts catalogs reviewed by Reuters. Delphi told NHTSA that it supplied the switches for the 2003-2007 CTS and the 2004-2009 SRX.

The Delphi documents did not make clear whether earlier versions of the Cadillac SRX had ignition switch issues. Neither the SRX nor the CTS has been recalled for ignition-switch related issues. GM did not immediately respond to request for comments.

The original Cadillac ignition switch and the original Saturn ignition switch carry similar GM part numbers: 12450257 for the 2004-2006 SRX and 12450250 for the 2003-2006 Ion.

GM requested a change to the Cadillac SRX ignition switch in early 2006, months before the relatively unchanged 2007 SRX went into production, because "test drivers (were) turning off the car with their knees while driving," Delphi told NHTSA.

GM engineers experienced similar issues in the Ion and Cobalt, but several times rejected design changes to the ignition switch until 2006. The Ion and Cobalt were not recalled until 2014, despite NHTSA receiving hundreds of consumer complaints over the past decade about engines stalling in those cars.

GM sold far fewer of the Cadillacs -- just over 200,000 CTS sedans and nearly 60,000 SRX crossovers from 2002-2005.

NHTSA received at least a dozen complaints about engines suddenly stalling in the 2003 CTS and another nine complaints about engines stalling in the 2004 SRX, a Reuters review of NHTSA complaint data show.

There are many potential reasons an engine could stall, and most of the complaints do not specify ignition switch issues. Some referred to the engine stopping when hitting a bump, which can be a switch-related problem in recalled vehicles.

The driver of a 2003 CTS, in a complaint filed in April 2014, described an incident in February 2006 where the engine would shut down "when the vehicle would hit a pot hole or hard bump."

The same driver, after hearing recent reports of ignition switches being jostled or bumped off in other GM cars, said, "I went out to my vehicle and started it, put the vehicle in drive and smacked my key ring and the vehicle stalled."

In a complaint received in 2004 about engines stalling in the 2004 SRX crossover, another driver said that the vehicle "goes from 65 mph to 0 (and) you have no control over the car at this point."

The complaint database does not include names or contact information. NHTSA did not respond to a request for comment on the Cadillac switch or consumer complaints.