Average credit scores on U.S. car loans rose to a six-year high in the fourth quarter, a report said Tuesday, a sign that lenders are raising their standards as more borrowers fall behind on their bills.

The median credit score for car loans made in the quarter rose to 707, according to the Federal Reserve Bank of New York's report on household debt. That's up two points from the third quarter and the highest level since 2011, when lenders were ratcheting up lending standards in the wake of the Great Recession. 

The credit score for loans in the 10th percentile, or those that are weaker than 90% of borrowers, rose two points to 575, the highest since 2010. Consumer credit scores typically range from 300 to 850, and borrowers below 620 are often viewed as subprime.