Most large banks appear to have been sailing through the annual "health checkups" they have had to undergo since the financial crisis.
But on Monday, the Federal Reserve described some significant shortcomings in the banks' responses to the so-called stress tests.
Despite the severity of the recent housing crisis, the Fed said some banks were not taking into account the possibility of falling house prices when valuing certain mortgage-related assets for the tests.
In other cases, banks assumed they would be strong enough to take business away from competitors in times of stress.
The Fed's findings are part of its efforts to improve the stress tests, which aim to ensure that banks have the financial strength to withstand shocks in the economy and markets.
The tests have created tension between the Fed and the banks. One reason is that the tests can determine how much a bank is allowed to pay out in dividends or spend on stock buybacks.
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In March, the Fed announced that two out of 18 banks had effectively failed the latest tests. One was BB&T, a regional bank based in Winston-Salem, N.C. The other was Ally Financial, a consumer lender that has struggled to right itself since the financial crisis and still has not fully repaid its bailout money to the government. Also in March, JPMorgan Chase and Goldman Sachs passed the latest tests, but the Fed said their responses contained weaknesses, and the banks were required to resubmit their plans by the end of September.
"We continue to work with the Fed and will resubmit in September," Goldman Sachs said in a statement.
In its review released on Monday, the Fed appeared most concerned that banks were applying the tests too generally. In other words, banks did not pay enough attention to the risks that were particular to their assets and operations. Banks excluded material that was relevant to the bank's "idiosyncratic vulnerabilities," the Fed said.
Under the tests, the banks have to assume weakness in the economy and turmoil in the markets, and then calculate the losses they would suffer under such conditions. The banks then subtract those losses from capital, the financial buffer they maintain to absorb losses. If the assumed losses cause capital to fall below a regulatory threshold, the banks effectively fail the test.