Wells Fargo & Co. is examining its wealth and investment management business for potential customer harm, and has found that some customers were overcharged because of technical-system errors, according to a securities filing on Thursday.

Wells, the third-largest U.S. bank, has been embroiled in a sales-practices scandal in its retail operation for well over a year. Problems in other areas including mortgage lending and auto insurance have surfaced through internal reviews and regulatory probes, but until now the wealth business has remained relatively unscathed.

The bank's board of directors is looking in to whether wealth and investment management customers experienced inappropriate referrals or recommendations, according to its 10-K filing with the U.S. Securities and Exchange Commission. The review includes rollovers for 401(k) plan participants, certain alternative investments and referrals of brokerage customers to other businesses.

Additionally, a review of fee calculations in Wells Fargo's investment and fiduciary services business has found that some customers were overcharged due to "incorrect set-up and maintenance in the system of record," according to the filing. Wells is now trying to determine the extent of damages and root cause of the problem.

The U.S. Justice Department instructed Wells Fargo in late 2017 to investigate its wealth management business after whistleblowers accused the bank of pushing inessential products or services on customers, the Wall Street Journal reported earlier on Thursday.

Wells Fargo declined to comment on the article. The Justice Department did not immediately respond to a Reuters request for comment.