I bought a Stant #10504 locking gas cap for my '09 Taco. A couple of you asked for feedback. First of all, it fit. Secondly, after about 80 miles the "check engine light" has still not come on. So I guess it works.
This cap was made for '07 and prior Tacomas, but a representative from Stant assured me it would fit the '09. It will not fit the '08, when Toyota went to a push-in cap, whereas this is a screw-in type.