P0136, p0137 and high fuel consumption

Hi all,
I have a 2008, 4x4, 4.0 Tacoma with 158k miles (without tow package).
I just did a 5k trip to CA with it. Eng light came on a few time while going there and on the way back eng light was on through out the return trip. I was getting about 17 mpg initially, but at the end I was down to 11 mpg.
Codes I have: p0136, p0137 bank 1 sensor 2, and p0606.
Sensor 2 is downstream o2. Would a Bad downstream o2 sensor causes such increase in fuel consumption?
Should I start with changing the downstream o2 and then see what happens?
I appreciate any guidance.

 

Your sensor is failing. Replace as soon as possible.

Might be kinda expensive, but necessary.

Screws with the ECM immensely.

Try RockAuto Good Luck!

 

Which sensor should I replace?

 

Bank 1 Sensor 2 is passenger side downstream.

Actually P0606 is a PCM internal processor code but I have seen that code set when there is an O2/AFR sensor problem.
Cyl 6 misfire would be P0306

 

Oops not enough coffee

You're right, I wonder if the heater circuit shorted into the sensor circuit or vice versa

 

Possibly, I see that happen on older GM's from time to time. They will typically misfire on one bank because the O2 sensor reports rich and the PCM pulls all the fuel on that bank, or they will report lean and it excessively overfuels on that bank.

 

DM93,

Thank you for the schematic. But my concern is that a bad downstream sensor would not cause my MPG drops to 10!!! I can start changing parts, in this case sensors, until eventually find which one was really the bad one, but I was hoping maybe I could get help identifying the problem before just changing parts based on code alone (as you have in your helpful videos)

 

Sometimes the computer will look at whichever oxygen sensor(s) it wants for fuel control. If the downstream sensor is coding the computer is trying to tell you it's got a fault, really need to start there..

 

Definitely not a bad idea, I would want to look at fuel trims and AFR/O2 sensor data and compare bank to bank as a first step.
The downstream sensors do have some input on fuel control although not nearly as much as the upstreams.

If circuit integrity is good and there are no obvious base engine issues causing O2 sensor codes such as vacuum or exhaust leaks I'm typically gona put a sensor in it for an O2 code that doesn't appear to be caused by anything else because I've seen quite a few times where they will operate normally at one moment and get goofy at the next moment.

 

I know that there is not exhaust leak, because if it was, I could hear it during my 2500 miles return trip, with the Eng. light on.

Well, at this point, I think my best option is replacing bank 1, sensor 2 and see what happens.
does 48$ for a Denso sounds right?

 

Possibly but I wouldn't reccomend buying anything like that off Amazon or ebay. Too many fake "OEM" and name brand parts on those sites.
If your buying online go with Rock Auto or a verified dealer. If buying locally go with a Denso from an auto parts store or dealer.

 

I Agree. Amazon has become a “Buyer Beware” marketplace. I’d go with the one from RockAuto at $44

 

I was under impression if seller is Amazon, then we could trust the item would not be fake.
Anyhow, I ordered one from Rockauto, and will post the results when I install it.

Thank you all for your input.