02 Sensor Check Engine Lights

[dta1984]

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?

 

[dta1984]

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.

 

[112motorsports]

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..

 

[dta1984]

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 ; http://www.toyota-4runner.org/4th-gen-t4rs/173760-oil-wicking-up-my-o2-sensor-wire-harness.html

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

 

[112motorsports]

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.

 

[dta1984]

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!

 

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Help w/ P0051 Code (4th Gen - O2 Sensors Already Replaced)

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