SACRAMENTO — The state Department of Motor Vehicles admitted Monday that it may have incorrectly registered 1,500 people to vote, including some who were not citizens of the United States.

It was the latest embarrassment for the DMV, which said last month that it had included errors in voter registration data for 23,000 people. Gov. Jerry Brown ordered an audit of the agency after that disclosure, which came on top of weeks of criticism over hours-long waits at DMV offices for people trying to obtain or renew driver’s licenses.

The DMV said none of the errors it may have made in registering people to vote involved undocumented immigrants, who are eligible to sign up for driver’s licenses in the state.

The agency said an internal audit found that DMV employees may have improperly registered 1,500 people at field offices between April 23 and Sept. 25. The DMV notified Secretary of State Alex Padilla of the possible errors in a letter Monday, saying that any mistaken registrations were “through no fault of the customer.”

Padilla responded that he is “deeply frustrated and disappointed” by persistent errors that “undermined public confidence in your basic responsibility to collect and transmit accurate voter registration information.” Padilla urged the department to hire an outside agency to review technology and practices that led to the failures.

The latest problem occurred when DMV customers, including some noncitizens, accidentally filled in the wrong voter eligibility response on driver’s license applications and asked staffers to make the corrections, the audit said. The revised responses were not correctly logged.

The error has since been fixed and affected customers will be notified, the DMV said.

Last month, the DMV said it had botched voter registrations for 23,000 people by putting the wrong political party and vote-by-mail preferences for those Californians. Those errors occurred when DMV technicians had more than one customer record open on a computer at the same time, causing those records to merge. Updated software and staff training will prevent the mistake from occurring again, DMV officials said.

“We have worked quickly with the Department of Technology to correct these errors and have also updated the programing and added additional safeguards to improve this process,” DMV Director Jean Shiomoto said in a statement Monday.

Assemblyman Jim Patterson, R-Fresno, said extensive issues in the DMV highlight the need for new leadership.

“There is much more to see here than what the DMV is admitting to,” Patterson said. “They have either been hiding the truth from the public or are completely unaware of this voter registration disaster — either should be a startling realization for this governor and the public. ... We cannot trust the current management to fix the very problems they created.”

Melody Gutierrez is The San Francisco Chronicle’s Sacramento bureau chief. Email: mgutierrez@sfchronicle.com. Twitter: @MelodyGutierrez