Timothy J. Sloan, chief executive of Wells Fargo, abruptly stepped down Thursday as one of the country’s largest banks struggles to recover from a series of self-inflicted scandals.

Sloan, who has been at the company for 31 years and became chief executive in 2016 after his predecessor resigned under pressure, has been facing criticism about the bank’s culture and sales practices. The bank said it would look to an external candidate — an apparent acknowledgment that promoting from within had failed to achieve the necessary changes.

Wells Fargo said Sloan, 58, would be replaced by the bank’s general counsel, C. Allen Parker, on an interim basis as it searches for a permanent chief.

Wells Fargo has been reeling since it admitted in 2016 that it had for years opened thousands of fictitious accounts in customers’ names, improperly charged them fees and sold them unwanted products. Last year, the Federal Reserve punished Wells Fargo by barring the bank from expanding until it cleans up its culture and establishes better internal checks and balances.

It wasn’t clear what prompted Sloan to tender his resignation. He appeared before a congressional committee this month and defended his work repairing the bank’s practices and culture.

Lawmakers from both parties attacked his record, citing a report by The New York Times that described how many Wells Fargo employees felt they remained under intense pressure to reach the types of internal sales targets that bank executives had insisted were no longer in force.