SANTA MONICA, Calif. -

For the fourth straight month, Subaru leads the pack with an A-plus in both manufacturer and brand rankings in TrueCar.com’s Performance Scorecard program.

In the manufacturer grading in the September rankings that were released this week, tying for second place were Toyota and BMW, both of which earned an A for the month. Jaguar Land Rover ranked third among OEMs, as its grade dropped from an A to an A-minus.

TrueCar’s Performance Scorecards grade automotive manufacturers and brands for their performance on eight different measurements including pricing, sales, incentives, customer loyalty, market share, and days in inventory.

Near the bottom of the manufacturers list were Nissan and Mitsubishi, tied with C grades; Suzuki with a C-minus; and Volvo with a D-plus.

The manufacturers with the largest gains from August to September 2012 were Porsche, which moved from a C-plus to a B, and BMW, which moved up from an A-.

Showing the steepest declines among manufacturers for the period, according to TrueCar.com, were Jaguar Land Rover; General Motors, which moved from a B to a B-minus; and Ford, which moved from a B-minus to a C-plus.

Rankings By Brand

In TrueCar’s brand rankings, Subaru and Scion tied for the first spot, while Land Rover, and Toyota and Lexus tied for second.

The third-place ranking was also a tie, between Fiat, Jeep and BMW.   

On the low end of by-brand rankings were Mazda, Smart and Jaguar, all earning D-plus grades; Volvo and Mitsubishi, each with D grades; and Suzuki with a D-plus.