I just completed a wild goose chase after replacing both O2 sensors. P0036 code bad heater element for the after cat sensor. A new scanner and hours of diagnosis and it was simple and now could be hard to fix. I must have strained the connector area when I disconnected the old sensor. Take connector off mount and wiggle it BANG the engine light goes out and everything checks out. Now how to find and fix an intermittent wiring problem. My old mentor a chief engineer who trained me said "first make sure the switch is turned on, then 90% off the time it is 'connectoritis' " . This time self induced; always watch out for assumptions. Now to find the intermittently bad wiring fault I created in the harness. UGH