Navistar has appointed former Textron CEO Lewis Campbell as interim boss, the company said in a statement.
"I look forward to working with Navistar's strong leadership team and talented employees, as we continue to take steps to provide dealers and customers with best-in-class products, enhance the Company's competitive position and build on Navistar's platform for generating profitable growth," Campbell said in the statement.
"At the appropriate time, we will conduct a search for a long-term CEO, which will include internal and external candidates."
Investors have been calling for Ustian to step down after a difficult year for Navistar, according to the Chicago Tribune.
Reuters reported the company has struggled to win US approval for an alternative pollution-reduction technology. Its shares have fallen 39 percent since the start of the year.
As Navistar's bottom line sank deeper into the red, Ustian changed course this month and announced the company would adopt a pollution-reduction system used by the rest of the truck industry.
Compounding its problems, Navistar revealed this month it was the subject of another US Securities and Exchange Commission investigation into “accounting and disclosure matters.”
It also forecast an adjusted third-quarter pre-tax loss of $80 million to $115 million and withdrew its full-year guidance.
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