Your Toyota Tacoma's front Catalytic Converter takes the bulk of emissions reduction load. Since the rear has already been replaced we suggest focusing on the front CAT. After all other emission systems have been inspected for proper operation you may suspect the catalytic converter. Since you need to check "one" specific catalytic converter it would be best to use the "intrusive" CAT Test method. The Intrusive CAT Test requires an emission sample be taken prior to and after the CAT which is being tested. During the test you should see at least a 40% decrease in emissions after the CAT. A 5 Gas Analyzer will be required to perform this test.
A simpler test, but less accurate, is a Temperature Test. Using an inferred thermometer measure the exhaust temperature at the CAT's inlet, and then measure the temperature at the CAT's outlet. You should see at least a 600 degree temperature increase at the outlet. Perform this test only after your Toyota Tacoma has been properly warmed up and while the engine is at high idle (2500rpm). Be careful as the exhaust components will be very hot.
