It means that your PCM has detected somethign wrong with your egr system. I have never done this to a toyota, and don't even know which parts it has and doesn't have. follow along and check what applies first. your egr system is something that recycles unspent gasoline vapors back into your engine. fixing it will improve your mileage, and make you pass an epa test!!
possibe causes of insufficient flow:
bad dpfe sensor-notorious in fords for failing, it measures the pressure of the system
clogged tubing from valve to vacum- very possible, they twist and turn all over the place, a piece of carbon could easily get stuck in there
bad evr (the vacum pump that controls the whole thing) the little motor in the vacum could have burnt out
bad egr vavle-highly unlikely, but possible
ccraked or leaking hose-first check the ones connected to the dpfe sensor itself.
bad pcm-uh-oh. that's pricey. but unlikely.
first, check the hoses. then go to autozone and get a new dpfe. 20 bucks. then clean out all ports, then test the vacum.
good luck
mb