Alright I figured it out!

Credit to UNSNUB on tundra solutions . I came across the following statement from him "The air fuel sensors have thier own fuse located in the same box you pulled off. It is a 15 amp fuse called AF Heater and also there is a relay called AF Heater Relay."

Then it hit me..... I was on a roadtrip and got the flashing AC light. I ended up swapping the mag clutch relay with......the af heater relay to get the AC working.

I swapped the relays and now the codes are gone. I'll update if they come back.

Welp, that didn't fix it. The light came back on after about 100 miles. This time for the original code, driver side downstream. My next step is to inspect all of the wiring again real good. Really stumped on this one.

I've been looking for my Haynes manual, but I can't find it. Does anyone happen to have the torque settings for the O2 sensors on the 2004 V8?

I've had the same problem with O2 sensors on my '04 V6 and I'll share with you what I found.

When the O2 sensor codes started appearing I went to my parts store and ordered Denso brand replacement sensors. Several weeks later the codes reappeared. I replaced them and a few weeks later the same thing. I then found a Toyota Tech. Service Bulletin that stated aftermarket O2 sensors have a different sensing range and will throw a CEL code. The TSB said to use only Toyota parts to correct this. About a week ago I ordered and installed factory parts and the CEL is off, for now. I also went to the dealership for the parts and install as I want them to be responsible should this be become reoccurring. It also cost a crap load of $$$ for the dealer to do the job but I was frustrated with dealing with this.

So, I would recommend first finding the TSB on this website and review it then contact different dealerships for the O2 sensors as they all seem to charge a different price.

Chris

The oldest scam the Engineers working for the Auto Mfg industries ever came up with, the engine trouble code telling people they need to replace O2 Sensors.
And it seems to be working as good today as it did years ago, as i keep reading people are still spending their money chasing them codes that just keep coming back.

So the original code p0156 bank 2 sensor 2 is the code that is on again. This is the sensor I replaced twice (both densos ).
For those that don't know, if you use the torque app to read Bluetooth obd codes, you can graph each 02 voltage. Below is mine. There is no voltage shown on bank2 sensor 2 and also the front two . Do I replace bank 2 sensor 2 again?

Attached Images

 

Yep....i'm still here, still chasing these codes lol.

Currently, P0136 and a pending P0174. Both downstream sensors have been changed twice. I've got a new A/F relay on the way to try that.

Is it possible that one or both CATs are bad? How do I identify this?

Still runs good, gas mileage consistently 16-17 mpg....which is a few mpg low compared to a few years ago when no codes.

Bump to the top. I have had the same problem and I am about to drive this truck into the lake. Here is what has happened with mine.

Bought The truck with 130k on the clock and from the previous owners records the upstream sensor on bank 1 was changed at 90k.

Ran great for 10k miles. Then the downstream drivers side failed and I replaced it. Ran good for 5k

Then both upstream took a dump changed both of them ran good for 10k.

Changed all 4 and they lasted all of 3k.

Now I have PO136 code back on.

I have tried everything, non fouler trick just today and the code came back on after 50 miles

My questions is do all these sensors share a common ground? If so is it a chassis ground or a grounded through the computer? This truck has been driving my crazy and I can't figure it out. HELP!!! I am going to look at the ECU for tans fluid etc. It just seems to me I ether have a faulty ECU or a bad ground. Everything starts with a P171 code, then upstream bank 1 then downstream bank 1, then downstream bank 2, then upstream bank 2. It all seems to make a loop, this is why I am thinking it is a ground problem especially is they all share the same ground.

Thank for any and all help..

Read through this thread ; oil wicking up my o2 sensor wire harness?

That is what's causing my lights (as well as another member with similar symptoms)

Well I just pulled the glove box and unplugged all 5 connectors and second one from the top had a tiny film on it. I realize any amount of oil should not be there however do you think this would be enough to potentially set this chain of reactions off? I have CRC electrical connector spray and I assume this will be sufficient to clean the ECU and the wire connectors. I plan on doing all 5 while I am in there. Should I also look at the box to the right? I think it was blue and or had blue connectors. Thank you for all of your help. I hope I am going in the right direction.

I'm not positive what the box on the right does...maybe that's the transmission computer? I wouldn't worry about that one.

I'd also check the actual 02 sensor plugs under the vehicle. Mine are very saturated. At this point, I do think the fluid in the 02 plugs does interrupt the voltage signal the sensor is sending the ECU...therefore triggering the light. I cleaned all of my plugs with electrical cleaner and compressed air. My light still came back on within 100 miles. The more permanent fix is to splice in solid core wire to block the fluid travel. Come join us in the other thread!

Hi there,

Similar to this issue, I have been struggling to fix a P0051 code on my 2005 SR5 (V6 / 4.0L). I recently failed emissions for high NOx, with the check engine light also being on.

I have replaced both Bank 2 sensors (Sensor 1 upstream of CAT and Sensor 2 downstream of CAT) and am still seeing the issue after clearing the code. The A/F relay and fuse also appear to be good, with no noticeable damage on the sensor wiring or pins.

When running diagnostics, I am seeing both upstream sensors (B1-S1 & B2-S1) fluctuating around 3.3 V nominal, which seem to be behaving normally. On the downstream sensors, B1-S2 seems to fluctuate within the 0.1 V to 0.9 V range I have seen called out on some of these threads, however, B2-S2 generally reads around 0.035 V, occasionally reaching up to 0.115 V.

I believe all the sensors are good, but it seems like there is an issue with the connection to the B2-S2 sensor based on the OBD data. As mentioned, the wiring looked good so I'd like to check the voltage at the ECM but am struggling to find a good pin-out to identify which pins I should be checking for B2-S2. Does anybody have a good diagram or photo to help understand?

Any other thoughts on how to solve this problem would be greatly appreciated.

Thanks,
Ryan