Was getting intermittent P0420 errors for quite some time. Don't live where emission testing is required so didn't worry about it since it seemed to have no effect on the way the Vibe performs. One day it came up with the P0031 so I replaced the O2 Sensors No longer get the P0420 but the P0031 won't go away. The troubleshooting for this includes checking a fuse for the sensor heater circuit but I can't find where that might be, if it actually exists. As you all probably know, there are 4 wires to each sensor. Do you know which two are the power for the heater?
My diagram shows purple or purple with black stripe for power, black for ground. My diagram also shows no fuse in the circuit. The heater is powered by the ECM.