Hello,
I have a 2008 Ford Ranger Sport, RWD, 3.0L. Today I received a check engine light, upon scanning, it came up as 2 Sensor Signal Biased/Stuck Lean Bank 1 Sensor 2. After some research, I was able to discover that this should be a downstream O2 sensor (after the catalytic converter). My truck has two cats that after them, converge into a signal exhaust pipe. As per my workshop manual and examination of my vehicle, I can only find O2 sensors upstream of the catalytic converter. This is also backed up by research done on other websites (https://ricksfreeautorepairadvice.co...sor-locations/). My OB2 reader picks up a signal from a bank 1 sensor 2 sensor, with voltage fluctuating from 0-0.6 volts, from my understanding, the voltage should not be fluctuating this much on a downstream 02 sensor, especially because it is fluctuating constantly. Can anyone help?

Thank you

 

Welcome to the forum

Yes, O2 sensor "1's" are upstream
O2 sensors "2's" are downstream

Bank1 is passenger side, Bank 2 is drivers side of "V" engines, 4cyl engines just have Bank 1

Only Dual exhaust systems would have a Bank 2, sensor 2(B2S2)

O2 sensors ONLY SEE Oxygen not fuel, 0.1volts is high oxygen(lean), 0.9v is low oxygen(rich)

Yes, the down stream O2 should be more steady than upstream, and with voltage 0.7 to 0.8v because Cat converters burn up most of the Oxygen when burning up pollutants
But computer does adjust air/fuel mix to make downstream O2 voltage drop then come back up to test that it and upstream O2 are responding as they should

O2 sensors are the ONLY sensors that can wear out, they use a chemical to detect Oxygen and they run out, after 100k miles or 12 years you should change them

So I would get a new O2 sensor and install it, all 3 O2 sensors are the same kind, narrow band, part number differences are for the length of attached wiring on the O2 sensor, and the connector
O2s all come with 4 wires attached and a plug in to match vehicle plug

If you have an automatic the downstream O2 wires were usually with the transmission wiring harness, on drivers side of trans, then the O2 harness ran over the top of trans to the passenger side and to the O2 sensor, its on or behind last Cat converter

Downstream O2 sensor is there, just hard to see, must look for it when engine/exhaust is stone cold

Your link confirms that location "Heated Oxygen Sensor (HO2S) #12 (A/T) Near right rear of transmission, in exhaust."

O2 sensor "12" is bank 1 sensor 2

Unfortunately if new O2 sensor doesn't fix the issue, then 1 or more Cat converters is bad, so $$$
O2 sensors do wear out so need to be changed regardless, which is why you do that first

 

Thank you so much, I really appreciate you explaining this to me. I just want to confirm, I have attached a picture of my workshop manual, these are the sensors in the exhaust system for my truck. Are you saying that item 8 in the diagram would be the downstream sensor? Because it states it as a catalyst monitor sensor. I ordered a downstream O2 sensor, would this work as a replacement?

Thanks again

 

Yes, that's what Cat monitor sensors are called, downstream O2 sensors, and yes #8 would be the B1S2 the code refers to
Drawing is an odd set up for single exhaust system, someone wanted to make some extra money
2 Downstream O2 sensors for a single exhaust pipe system is WAY OVERKILL