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.

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!

 

I'd suggest taking a close look at why it got sooty. If it hasn't seen new plugs in a while, I'd change them. Maybe run a fuel injector cleaner like Techron or Gumout with Regane. With any ECU engine with O2 sensors, once the output at the sensor starts to fall(soot covered), the ECU adjusts the injectors for that side richer. The richer the more soot. So exponentially, it's a downhill spiral for it. But I would take a look at the plugs. See any black ones, better get it changed or expect issues at the Cat. May even have to go as far as checking the compression on that side.

 

Labnerd, those are the downstream sensors after the cats if that makes a difference in your diagnosis.

 

Plugs prolly have 30K on them. I change them out regularly (when I change tranny fluid) with stock Autolites. But they're due, so I'll check. Can a faulty injector cause a rich cylinder?