When I bought my truck two years ago, it started throwing all sorts of codes. As I sorted them out, the last one I was dragging my feet on was replacing the EVAP canister, which I was told the switch in it had completely failed and Toyota only sells the entire thing as a whole unit. Finally, $600 later, I installed it this February. A few weeks ago, my CEL light came back on, and the codes and suggested fixes all point to the EVAP canister again. What, from a mechanical perspective, would cause an EVAP canister to fail that fast? It is an OEM part, directly from Toyota. I wonder if there is a bigger issue going on with my truck to cause the canisters to fail?