The company announced Tuesday it was recalling 2.1 million gallons of regular gasoline that was made at the northwest Indiana plant.
BP says the foul fuel has a higher than normal level of polymeric residue, which makes it hard to start the cars and other issues.
The attorney general says he launched an investigation to make sure consumers were protected.
So far, more than 5,000 BP customers have complained their cars have been damaged because of the tainted gas.
Any customers with expenses related to the recalled gas will be reimbursed, BP says. A BP spokesperson said Tuesday that expenses must be documented and customers should save receipts and itemized information.
The customer service phone number for BP is 1-800-333-3991. Customers can also e-mail firstname.lastname@example.org.