The October query put the North American supply base at a score of 48 out of 100 on the index, down from a 50 in July.
Charles Chesbrough, OESA chief economist, said the seemingly small drop puts the industry sector into a "pessimistic" category.
"A score below 50 suggests suppliers have a negative view on their company's business outlook," Chesbrough told Automotive News.
The index level of 48 is the gloomiest outlook the supplier industry has evinced since 2012, when global production disruptions followed the 2011 Japanese earthquake and tsunami.
Chesbrough said the OESA Barometer has revealed a steadily deteriorating supplier outlook since 2013, despite the industry posting big vehicle sales volumes every year.
Three factors loomed large in the industry's anxiety, he said:
1. Many suppliers feel U.S. consumers are simply holding back on their spending, making the general economy more anemic than it should be.
2. Some suppliers are daunted by lower-than-expected sales of specific vehicle models they are supplying. That is a change from more robust days since 2013, when almost all vehicle segments were growing in the years after the Great Recession.
3. Some parts makers also are apprehensive about November's U.S. presidential election and the impact it may hold. Some are specifically concerned about how they might be affected should a new administration reopen the North American Free Trade Agreement, Chesbrough said.
Concerns about NAFTA and charges that it has encouraged manufacturers to shift capital investment from the United States and Canada to Mexico have been a hot topic during this year's presidential campaign. Republican candidate Donald Trump has vowed to renegotiate the 1994 free trade agreement if he is elected.
Chesbrough added that one issue that has concerned suppliers on recent OESA barometers -- their difficulty in finding enough workers and engineers to keep up with customer volumes -- appears to have abated.