Lindsay Lohan[FONT=Arial, Helvetica, sans-serif]'s  brakes couldn't have failed last month -- moments before she slammed  her Porsche into an 18-wheeler -- because sources tell TMZ, Porsche  itself tested the car after the crash ... and the brakes passed with  flying colors.[/FONT]
[FONT=Arial, Helvetica, sans-serif]TMZ broke the story ... Lindsay blamed faulty brakes[/FONT][FONT=Arial, Helvetica, sans-serif] for the accident.-- telling friends she slammed on the brakes when the truck allegedly cut her off ... and nothing happened.[/FONT]
[FONT=Arial, Helvetica, sans-serif]As  it happens, we're told Porsche caught wind of Lindsay's excuse and  contacted the company that rented Lindsay the vehicle -- asking if it  could formally test the car.[/FONT]
[FONT=Arial, Helvetica, sans-serif]According  to sources, the rental company obliged -- and Porsche ran its tests,  finding the brakes that had been installed on the car were A-OK, and  showed no evidence of malfunction ... which blows Lindsay's bum brakes  excuse out of the water.[/FONT]
[FONT=Arial, Helvetica, sans-serif]A  rep for the Santa Monica PD had no comment. A rep for Porsche also had  no comment -- but did say they're cooperating with authorities. Calls to  Lindsay were not returned.[/FONT]