I bought my Camry used w/135000 miles. At about 149000 miles the Mil light came on. I plugged in my code reader, and it produced 3 codes-PO420, 440 & 446. I replaced the emissions canister and cleared the codes. About 2 months later, the light came back on, this time only the PO420 code. I purchased software and an interface cable to connect my laptop. When I set to monitor the 02 sensors, I get a graph and voltage readings for short term fuel trim, but nothing for long term fuel trim. The car runs fine. I don't see any smoke and there is no performance problem. Can you offer any insight?