The plaintiffs' attorneys said Bosch had worked with Volkswagen to develop a so-called cheat device to circumvent US emissions tests
Auto supplier Robert Bosch GmbH said claims it was a knowing participant in Volkswagen's decade-long scheme to evade US anti-pollution laws were "wild and unfounded."
In a filing in US District Court in San Francisco late on Monday, Bosch responded to attorneys who are suing Volkswagen AG on behalf of US owners of the polluting VW diesel vehicles, who had said Bosch was a "knowing and active participant in the scheme"".
Bosch makes an engine control unit used by several top automakers including VW. It supplied software and components to VW but has said responsibility for how software is used to regulate exhaust emissions or fuel consumption lies with carmakers.
The plaintiffs' attorneys said Bosch had worked with Volkswagen to develop a so-called cheat device to circumvent US emissions tests and trick regulators.
The Bosch filing said an initial review of the plaintiffs' documents "indicates that the plaintiffs have made wild and unfounded allegations" that in some cases are based on speculation.
Most of the allegations involving Bosch remain under seal because the documents have been designated as confidential by Volkswagen.
Bosch said it did not oppose making public most of the allegations under seal, except to keep the names and job titles of Bosch employees confidential, citing strict German privacy laws. Bosch said the plaintiffs' complaint cites 38 Bosch employees - in addition to its chief executive, Volkmar Denner, who is a named defendant.
Bosch said the allegations are supposedly based on documents turned over by Volkswagen "but in many cases based only on speculation, and oftentimes directly contradicted by the terms of the documents cited."
Bosch has not been charged with any wrongdoing. German prosecutors said in December that they were investigating whether staff at the Stuttgart-based company were involved in the rigging of emissions tests by VW.
The engine control system for VW's clean diesel engine was customized through years of close collaboration between the carmaker and Bosch, plaintiffs' lawyers said.
Denner said in January he had ordered an internal investigation and was cooperating with authorities. In April, Bosch said it had set aside 650 million euros for potential legal costs, including for a continuing investigation into the company's role in Volkswagen's diesel emissions manipulation scandal.
In November the United States federal prosecutors were investigating whether Bosch knew or participated in VW's efforts to cheat on US diesel emissions tests.
In June, Deputy US Attorney General Sally Yates said the VW investigation is looking at "multiple companies and multiple individuals."
Reuters reported last week Volkswagen has held preliminary talks with the US Justice Department to settle a criminal investigation of the emissions cheating case.