NEW YORK (Reuters) -The bankruptcies of U.S. auto parts supplier First Brands and car dealership Tricolor have prompted soul searching on Wall Street, with JPMorgan Chase ( JPM ) saying it re-examined its controls after finding itself exposed, although banks broadly said that U.S. borrowers' credit quality is robust.

On post-earnings calls with investors, top executives at the largest U.S. banks and financial institutions, including Citigroup ( C/PN ), Wells Fargo ( WFC ) and BlackRock ( BLK ) said credit investing activity has been strong, despite some investor fears of a wider ripple effect slowing down the booming global business of corporate credit.

The twin collapses of First Brands and Tricolor in September have affected some pockets of Wall Street's multitrillion-dollar credit machinery, and forced some debt investors to cut exposure to certain sectors over concerns about weakness in consumer and auto lending.

"We've had a credit market bull market now for the better part of since 2010. ... These are early signs there might be some excess out there because of it. If we ever have a downturn, you're going to see quite a few more credit issues," said JPMorgan ( JPM ) CEO Dimon on a post-earnings analyst call on Tuesday.

"When you see one cockroach, there are probably more, and so everyone should be forewarned of this one," he added. "First Brands I'd put in the same category and there are a couple of other ones out there that I've seen that I put in similar categories. We always look at these things and we're not omnipotent - we make mistakes too."

JPMorgan ( JPM ) wrote off $170 million in the third quarter related to the Tricolor bankruptcy, and said it is reviewing its controls, with Dimon describing the bank's exposure as "not our finest moment."

"When something like that happens, you can assume that we scour every issue, every universe, everything about how it could be taking place to make sure it doesn't take place from here," Dimon said. "You can never completely avoid these things, but the discipline is to look at it in cold light and go through every single little thing, which you can imagine we've already done."

The bankruptcies prompted scrutiny into how exposed fund managers might be to troubled borrowers. Some large Wall Street banks including Jefferies and UBS have in recent days disclosed exposure to First Brands, and said the fallout is limited and any potential losses will be "readily absorbable."

A First Brands creditor has claimed that as much as $2.3 billion "simply vanished" from the bankrupt U.S. auto parts supplier, which is being probed by the U.S. Department of Justice.

"The teams are generally seeing strong credit quality from borrowers. Even in syndicated loan markets, default rates have been declining," said BlackRock ( BLK ) Chief Financial Officer Martin Small.

"We read the same headlines that you do about private credit bankruptcies, but those exposures are actually in syndicated bank loan and CLO markets - they're not with large private credit managers and direct lending books," he added, referring to collateralized loan obligations.

"The reported cases look more like idiosyncratic pockets of stress. They don't look like broad stresses on asset-based finance or consumer credit."

Earlier in October, BlackRock ( BLK ) requested to redeem some money it invested in a Jefferies fund that is exposed to the debt of First Brands, Reuters has previously reported.

Citigroup's ( C/PN ) finance chief Mark Mason said the bank sees no particular distress signs in corporate credit, and has no exposure to the recent bankruptcies.

Goldman Sachs CFO Denis Coleman said the bank has a consistent set of underwriting standards, and conducts robust upfront due diligence on deals.

"We have ongoing monitoring and reporting diligence underlying collateral. We manage the granularity of our portfolio within our own internally set diversification and concentration limits," said Coleman, noting that Goldman is not exposed to the debt held by First Brands and Tricolor.