CEL, VSC, and 4WD/TRAC Lights are on

What is your question?

I recently had a diagnostic test because CEL, VSC, and 4WD/TRAC (Check Engine Light, Vehicle Stability Control, and 4-Wheel Drive/Traction Control lights went on. The code was P0138-I had the Bank 1 Sensor 2 replaced yet the lights above went back on in a day or 2. I read that the problem may be a defective charcoal canister filter which costs about 1500.00 to repair. How can I determine what the real issue is before dishing out that much $$$. Will Toyota pay for those repairs if it is a defective canister filter? Thanks