Oxygen sensor replacement

Tiny
AVALON1995
  • MEMBER
  • 1995 TOYOTA AVALON
  • 3.0L
  • V6
  • 2WD
  • AUTOMATIC
  • 200,000 MILES
Can you please provide the procedure on how to replace the oxygen sensor on Bank 1 Sensor 2, the one after the catalytic converter? By any chance, does the passenger car seat have to be removed?


Thank you!


Cheers!
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Wednesday, November 18th, 2020 AT 3:03 PM

27 Replies

Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

The oxygen sensor is mounted on the exhaust system and on the exterior of the vehicle. It is located after the catalytic converter and before the resonator. See pic 1 for location.

Now, because there is a wire attached to it, you can't use a standard socket for removal. You have two choices. First, try to remove it with an open-end wrench. In all honesty, they are usually rusted in place and that type of a wrench usually will round off the hex, so don't allow that to happen if it seems too tight.

Second, you need to get a socket designed for the removal and install of an O2 sensor. It will be open on the side allowing the wire to be routed out of the socket. That is the best choice of tools.

You don't need to remove the seat. Also, when looking at the attached pic, make sure to read the text in the box.

Also, here is a link that explains in general how an O2 sensor is replaced. I thought it may be helpful for you.

https://www.2carpros.com/articles/how-to-replace-an-oxygen-sensor

Let me know if this helps or if you have other questions.

Take care,
Joe
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Wednesday, November 18th, 2020 AT 7:07 PM
Tiny
I-SMOGEM
  • EXPERT
After hours of searching for an answer to your question, the best I could come up with is for a 1997. Honestly, I don't know if the 1995 is the same.

https://www.youtube.com/watch?v=-ivgya9rOLo

Hope this helps... Glenn
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Wednesday, November 18th, 2020 AT 7:41 PM
Tiny
AVALON1995
  • MEMBER
My understanding is that the wiring harness for the downstream O2 sensor is located inside the car under the front passenger seat. I have replaced the upstream O2 sensors in the past, so thankfully I'm familiar with how to do it. However, the downstream O2 sensor is more challenging. I couldn't find a video on YouTube for my car model, so the next best thing I found was for a 2001 Toyota Avalon. Are you sure that the car seat doesn't need to be removed? According to the video, it involves removing the front passenger car seat and the carpeting. Hence, I'm trying to find out if the procedure is the same for my car, a 1995 Toyota Avalon. I have attached the video link. Please let me know if it can be applied to my car or if it's a different procedure.

https://youtu.be/6fii05FVoNw

Thank you!

Cheers!
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Wednesday, November 18th, 2020 AT 7:42 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

Now that I watched the video, I do remember the wiring going under the seat. The best way to determine if your model year is the same is by checking if the wiring goes up into the floor of the vehicle. Have you checked that yet? If it does, then the seat and carpet will need to be moved.

Joe
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Wednesday, November 18th, 2020 AT 8:39 PM
Tiny
AVALON1995
  • MEMBER
I have gone on the underside of my car and have seen that the wiring does indeed go up into the floor. I guess that video is going to come in very handy.

Btw, how can I even determine if the downstream O2 sensor needs to be replaced for sure? I don't have a check engine light on. The live data on my scan tool indicates that the voltage for my upstream 02 sensors fluctuate just as they are supposed to. However, my downstream O2 sensor (Bank 1 Sensor 2), which is highlighted in blue in the attached video, remains flat at zero (0.000) both at idle and with the RPM raised above 2500. So what does that tell us? Does it mean that the O2 sensor is faulty? Is it even possible that the O2 sensor could be faulty, but not necessarily trigger a check engine light?

Thank you!

Cheers!
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Wednesday, November 18th, 2020 AT 9:46 PM
Tiny
AVALON1995
  • MEMBER
Were you able to look into my question from my very last post?

Thank you!

Cheers!
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Friday, November 20th, 2020 AT 5:08 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

Chances are, if the sensor is connected and the connection isn't damaged or corroded, the sensor is bad. You can check the resistance of the sensor itself.

If you check resistance, you should have between 11 - 16 ohms at 20 C.

Can you tell me what the code is you are getting?

Joe
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Friday, November 20th, 2020 AT 9:08 PM
Tiny
AVALON1995
  • MEMBER
Like I mentioned in my previous post, there is no code, in fact, there is no check engine light on. The Live Data on my scan tool indicates that the voltage for the downstream O2 sensor is zero. Have you seen the very brief video I had attached in my previous post?
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Friday, November 20th, 2020 AT 9:23 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

I did see it. The only thing you can do is visually inspect the wiring and connector. If that all appears good, check the resistance in the sensor. If the resistance is within spec, then we will have to start checking wiring and connections up from the sensor.

Joe
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Friday, November 20th, 2020 AT 9:35 PM
Tiny
AVALON1995
  • MEMBER
Checking the resistance will be my next step.
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Friday, November 20th, 2020 AT 9:38 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Sounds like a plan. Let me know what you find.

Joe
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Friday, November 20th, 2020 AT 9:49 PM
Tiny
AVALON1995
  • MEMBER
I have checked the resistance and it falls within the specs. What should I do next?
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Saturday, November 21st, 2020 AT 7:52 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

If the sensor is good, then you need to start tracing the wiring. First, make sure the connector is in good condition and free of corrosion. Next, make sure the wiring isn't damaged where it goes into the vehicle or near the sensor.

Let me know what you find.

Joe
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Saturday, November 21st, 2020 AT 8:59 PM
Tiny
AVALON1995
  • MEMBER
I tried to trace the wiring, but it's really not accessible. I wish I would have taken pictures or recorded it to show you what I mean. I think the center console would need to be dismantled or something to trace the wiring. Do you have the procedure and the diagram that illustrates how to trace the wiring?
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Saturday, November 21st, 2020 AT 9:19 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

When I trace wires, I have to follow a wiring schematic. They don't specifically tell you where the wire runs through the vehicle. However, it shows where the wires go to.

I attached several pics below. I started at the O2 sensor in question. I highlighted the wires from the sensor and traced them throughout the schematics so you can see where each wire goes. I don't know if it helps, but take a look through it and see if it helps you find the locations where the wiring goes. The pics are in order. If you could picture them laid out, one on top of the other, that is what I had.

I hope it helps.

Let me know.

Joe
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Saturday, November 21st, 2020 AT 9:32 PM
Tiny
AVALON1995
  • MEMBER
Just so that I understand, is the purpose of tracing the wiring is to conduct a continuity test or is there something else? As far as this car is concerned, there is no functioning downstream O2 sensor. Hence, what would be the downside of driving this car without a downstream O2 sensor?

Please let me know if I have this correct. From what I can figure out looking at the schematics, #1 (pink/black) and #3 (black) wires are connected to the ECM. The #4 (brown) wire is connected to the Junction Connector, where in the world is that? Is there a diagram that shows its location? Now, when it comes to the #2 (black/orange) wire, it's very confusing, because it seems like it's connected at several spots. Can you please explain what the deal is with that wire? Where is it connected to in reference to the downstream O2 sensor.

Thank you!

Cheers!
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Saturday, November 21st, 2020 AT 10:32 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
The brown wire is connected to those things under the instrument panel (see pics). The black/orange does jump. It branches from the circuit relay.

My manual doesn't show exact locations. Just general ones.

I hope you understand. As far as driving without that sensor, the car will run fine, but you may notice a decrease in fuel mileage. That is how the computer determines the air-fuel ratio that is needed.
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Saturday, November 21st, 2020 AT 10:43 PM
Tiny
AVALON1995
  • MEMBER
The purpose of tracing the wiring, is it solely to conduct a continuity test or is there something else?

I'm curious to find out why a check engine light has not been triggered with the downstream O2 sensor or the wiring not functioning?
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Saturday, November 21st, 2020 AT 10:54 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Since you are getting nothing when testing at the sensor and the sensor is good, I suspect the wire is damaged at some point or at the PCM. As far as the light not turning on, there could be an issue with the PCM. We will need to work back to it and if there is still nothing found with the wiring, then we will need to check at the PCM itself.

Joe
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Sunday, November 22nd, 2020 AT 7:40 PM
Tiny
AVALON1995
  • MEMBER
From what I understand, the voltage for the upstream oxygen sensors is supposed to fluctuate between 0.1 - 0.9. For the downstream oxygen sensor, my understanding is that the voltage is supposed to be steady, however, what kind of voltage should I see? At one point, for the voltage, I saw a reading of 0.020, 0.015, and 0.010 briefly. What does that mean?

I conducted a continuity test for the downstream wiring that are connected to the PCM and they all passed. What should be my next step?

Thank you!

Cheers!
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Tuesday, November 24th, 2020 AT 9:21 PM

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