Massachusetts Attorney General Martha Coakley is investigating Santander bank's subprime auto lending business over concerns that the company may be engaged in the type of predatory practices that, on a larger scale, led to the mortgage and financial crises of several years ago.

Coakley's office is looking at whether Santander lent to borrowers who were unlikely to repay the money and sold those loans to Wall Street, where they were packaged into securities and resold to investors.

Coakley has subpoenaedSantander's US auto finance company to produce documents related to borrowers' credit histories, the interest rates they were charged, and how the loan risks were described to investors, said Brad Puffer, spokesman for the attorney general. Coakley took a similar approach in investigations of subprime mortgage lending a few years ago.

"We are using our experience, gained in holding banks responsible for unfair and predatory mortgage loans, to ensure consumers are protected in other areas of lending," Puffer said.

He said the attorney general is questioning a handful of other auto lenders, whom he declined to name, and attorneys general across the country have launched similar investigations into auto loan practices.

Santander issued a statement saying that it is cooperating with investigators and that its policy is "to comply with all lending and loan servicing laws, as well as the rules and guidance of our supervisors and regulators."

The lending pattern at issue is one that many mortgage lenders followed in the run-up to the last housing bust, which ultimately resulted in widespread loan defaults, worthless securities, and the near collapse of the banking system. However, it is unlikely that problems in the subprime auto lending market would spiral into another financial crisis, largely because auto loans are only a fraction of mortgage debt and it's far easier to repossess a car to recover money than to foreclose on a home.

But regulators worry that losses from these loans ultimately will cost consumers in the form of higher interest rates and make it harder for credit-worthy customers to obtain auto financing, much as many people were locked out of mortgages following the financial crisis.

Santander, a Spanish bank with US headquarters in Boston, declined to comment specifically on the Massachusetts investigation. But its American subsidiary, Santander Holdings USA Inc., acknowledged in regulatory filings this fall that it also was subpoenaed by the US Department of Justice and multiple state attorneys general over its auto loan business, which accounts for nearly one-third of its US assets.

Earlier this month, the New York Department of Financial Services, that state's top bank regulator, said it issued subpoenas to Santander and six other auto lenders over discriminatory practices after it found a significant difference between interest rates offered to minority and other borrowers.

Bill Himpler, executive vice president at American Financial Services Association, a trade group that represents auto lenders, said some regulatory concerns relate to dealerships, not lenders. For example, he said, financial firms don't know the race of the car buyers.

Auto lending is a robust business and performed well in recent years even as consumers curtailed credit card, mortgage, and other debt. Auto loan debt among US households reached an all-time high this year, $934 billion, up 15 percent from 2007, when the recession began (mortgage debt was $8.13 trillion in the third quarter).

Lenders have made it easier for borrowers — even those with troubled credit histories — to drive cars home from dealerships, in part to meet the demand of investors. Subprime loans, which carry higher interest rates, are riskier but offer the potential of higher returns to investors.

"We've seen a lot of money chasing auto lending," said John Van Alst, an attorney with the National Consumer Law Center, a Boston advocacy group.

That has opened the door to potential abuses, as investor demand pushes institutions to make more loans, dealerships to sell more cars, and consumers to take on more debt. Auto delinquency rates jumped by 13 percent in the third quarter of 2014 from a year earlier, driven primarily by subprime lending, according to TransUnion, a credit information firm.

Santander became a dominant player in the subprime market in 2006, when it paid $636 million to buy Drive Financial Services, a Dallas lender specializing in subprime loans. Drive was renamed Santander Consumer USA, and its business has grown as it bought other auto lenders and built relationships with nearly 14,000 dealerships nationwide.

Santander officials say the company is trying to expand beyond the subprime market to borrowers with better credit histories and signed a deal last year to become the preferred lender for Chrysler's dealers. Still, 86 percent of Santander's car loans remain below prime, or for borrowers with credit scores below 620 points, according to its financial reports.

The company repossessed more than 166,000 vehicles through September of this year. In 2013, US lenders repossessed 1.4 million cars.

Santander Consumer is the target of the most complaints for auto lenders in the US Consumer Financial Protection Bureau's database.

Last month, Santander settled a lawsuit brought by two consumers who alleged that the bank failed to properly monitor a Queens dealership, called New York Motor Group LLC, where an employee who handled borrower financing was accused of falsifying loan documents.

Peter Lane, a Northampton attorney, who represented consumers in this claim, declined to comment. Santander also declined to comment on the case.

In a presentation to investors last month, Santander Consumer emphasized that it has strengthened oversight, including increasing staff that ensures the company and the loans that it approves comply with state and federal rules.

Van Alst, with the Consumer Law Center, praised regulators for paying more attention to auto loans, because for most consumers cars are crucial assets that help them get and keep jobs.

If they have to stretch to pay off a large car loan and let other bills slide, they will, Van Alst said, leading to other financial problems.

"It is hurting the individual consumers," he said. "They're not paying other bills to stay current on the car."

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Deirdre Fernandes can be reached at deirdre.fernandes @globe.com.