Auto loan delinquency rates showed improvement in the second quarter, but the latest research shows that outstanding auto debt rose in comparison to last year.

According to data compiled by Equifax, auto loan accounts 60-plus days past due dropped 2% year-over-year. While banks and credit unions saw delinquency rates decline, captive auto lenders had a 38% year-over-year increase. Delinquency rates across all credit risk tiers dropped compared to last year.

Total outstanding auto debt reached $1.7 trillion, up 2% year-over-year, and the total account volume was 87.4 million. According to Equifax, auto loans were a main driver of nonmortgage consumer debt.

"Historically, total student loan debt balances were consistently higher than auto debt and almost twice as much as bankcard debt," said Equifax advisory leader Emmaline Aliff.

"The changing proportions of the non-mortgage categories reflect a macro shift, where student loan stabilization is being offset by further reliance on credit to manage the budgetary pressures of rising household and vehicle costs."

The consumer credit reporting agency said total U.S. consumer debt reached $18.25 trillion in the quarter, up 2% year-over-year.