WASHINGTON (Reuters) -- U.S. lawmakers probing how General Motors used faulty ignition switches in many vehicles are turning their scrutiny to the supplier of the part, Delphi Automotive.
A group of senators on Tuesday wrote to Delphi CEO Rodney O'Neal, asking for information about whether the parts supplier pushed back against GM after the automaker apparently did not accept a proposed fix to the switches.
"It is our understanding that a fix was proposed by Delphi regarding the ignition switch in 2005 but GM did not adopt the change," the letter said. "As we continue evaluating the GM recall it is critically important that we understand the decisions made by Delphi and the company's interaction with GM."
Senate Commerce Chairman Jay Rockefeller, D-W.Va., signed the letter along with three fellow senators -- John Thune, the top Republican on the panel, Democrat Claire McCaskill and Republican Dean Heller.
A spokeswoman for Delphi did not respond to a request for comment.
Congressional investigators have so far mostly focused their attention on GM and the National Highway Traffic Safety Administration, which have both come under scrutiny for not acting on years of warning signs about the deadly defect.
GM has recalled 2.6 million vehicles, including Chevrolet Cobalts and other models with ignition switches prone to being bumped or jostled into accessory mode while cars were moving, which could shut off engines and disable power steering, power brakes and airbags.
The faulty part has been linked to at least 13 deaths. GM has hired former federal prosecutor Anton Valukas to conduct an internal investigation into the faulty switches and subsequent recalls.
Delphi officials have told investigators from the House of Representatives that GM approved the ignition switches, even though the parts did not appear to meet GM's own specifications.
Delphi has also been drawn into a mounting wave of litigation for its role in producing the faulty switch that prompted the recalls.
The senators on Tuesday asked Delphi whether the parts supplier originated the discussion to fix the part, or if GM did. They also asked for the reasons why a design change was rejected in 2005, if Delphi protested the decision, and if Delphi communicated with NHTSA about the ignition switch.
The senators asked for answers by April 28.
It is unclear if Delphi executives will be called to testify. After holding hearings earlier this month with GM CEO Mary Barra and the NHTSA chief David Friedman, lawmakers expect to zero in on GM engineers critical to the development and oversight of the faulty switches.