O2 Sensor (downstream) sooty ?

[Spike Strip]

Hello Folks, newb to this forum.

I recently replaced both the downstream O2 Sensors in my 2000 4.2L F150 because I was getting a P0136 (Bank1 Sensor 2) code that I couldn't get rid of by cleaning the connector or fixing wires. 110Kmiles. Calif truck. No other codes and has always easily passed smog tests.

When I pulled the sensors, the DRIVER's side unit was extremely sooty, as compared to the passenger side (bank 1). The code failure was on bank 1.

Is this normal or is there some rich condition on the driver's side bank that I need to check into ?

Originals were Bosch, replaced w/ Motorcraft, if that makes any diff.

One on left is driver's side unit.

Thanks!

 

[blacksnapon]

Think of it this way, all the downstream sensors are, are catalyst efficiency monitors. The o2 sensors could be doing their jobs, warning you of a bad catalytic converter.