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Catalytic converter test guide

Tiny
AVALON1995
  • MEMBER
  • 1995 TOYOTA AVALON
  • 3.0L
  • V6
  • 2WD
  • AUTOMATIC
  • 200,000 MILES
I'm trying to diagnose my catalytic converter, even though 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 (the one by the catalytic converter) remains flat at zero (0.000), which is highlighted in blue in the attached video. So what does that mean in regards to the catalytic converter?

I have also conducted a temperature test by using an infrared thermometer. My understanding is that the temperature of the outlet catalytic converter is supposed to be higher than the inlet temperature. In my case, the inlet temperature is higher than the outlet temperature. Hence, what does that tell us? Would that be a conclusive way of determining that the catalytic converter is faulty or would additional tests need to be carried out?

Also, if the braided part of a flex pipe has deteriorated, but the inside parts are still good and there is no exhaust leak coming from the flex pipe, is it necessary to replace the flex pipe?

Cheers!

Thank you!
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Wednesday, October 28th, 2020 AT 10:22 PM

7 Replies

Tiny
DANNY L
  • MECHANIC
  • 5,648 POSTS
Hello, I'm Danny.

Yes, by what you've stated you might have a partially plugged converter. The outlet temperature should be hotter than the inlet. Here are 2 tutorials showing catalytic converter testing and symptoms:

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

https://www.2carpros.com/articles/bad-catalytic-converter-symptoms

Hope this helps and thanks for using 2CarPros.
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Wednesday, October 28th, 2020 AT 11:14 PM
Tiny
AVALON1995
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Were you able to watch the video of the Live Data that I had attached? Can you please tell me what it means when the voltage of the downstream O2 sensor remains at zero? Is it possible that the catalytic converter could be bad, but still doesn't trigger a code in the check engine light?

Also, can you please address my question regarding the flex pipe?

Thank you!
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Wednesday, October 28th, 2020 AT 11:19 PM
Tiny
BMDOUBLE
  • MECHANIC
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That is how I like to tell the condition of the converters myself, so good job on that note! What you can do is spray the intake tract with brakeclean or throttle body cleaner to simulate a rich running condition, this should make the voltages in all oxygen sensors spike up. You could possibly just have a bad downstream oxygen sensor or a circuit issue.
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Thursday, October 29th, 2020 AT 6:37 AM
Tiny
AVALON1995
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  • 121 POSTS
If I have a bad downstream oxygen sensor, a circuit issue, or a bad catalytic converter, then wouldn't that trigger a check engine light? If the catalytic converter is bad, would that generate a zero voltage for the downstream oxygen sensor?

I'm curious to find out the answer to this question: If the inlet temperature is higher than the outlet temperature for the catalytic
converter, would that be a conclusive way of determining that the catalytic converter is bad or would additional tests need to be carried out?

Thank you!
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Thursday, October 29th, 2020 AT 3:21 PM
Tiny
DANNY L
  • MECHANIC
  • 5,648 POSTS
Hello again.

Here are your answers. If I have a bad downstream oxygen sensor, a circuit issue, or a bad catalytic converter, then wouldn't that trigger a check engine light? Answer- yes.
If the catalytic converter is bad, would that generate a zero voltage for the downstream oxygen sensor?
Answer-no.
If the inlet temperature is higher than the outlet temperature for the catalytic
converter, would that be a conclusive way of determining that the catalytic converter is bad?
Answer-yes.

As I've stated in the last post if the outlet temperature is lower than the inlet that shows the converter might be plugged or defective. The outlet temperature should always be higher to show the converter is operating efficiently. Hope this helps and thanks again for using 2CarPros.

Danny-
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Thursday, October 29th, 2020 AT 8:17 PM
Tiny
AVALON1995
  • MEMBER
  • 121 POSTS
Thank you very much for your reply to my questions.

Well, since I don't have a check engine light on, then how can you explain why the voltage for my downstream oxygen sensor is zero? What does that tell us? You can refer to the video of the Live Data that I have attached in my original post.

Furthermore, since the temperature test for the catalytic converter failed, then why has it not triggered a check engine light?

Thank you!
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Thursday, October 29th, 2020 AT 8:32 PM
Tiny
DANNY L
  • MECHANIC
  • 5,648 POSTS
Hello again.

It's possible you might have a defective o2 sensor or a signal-wiring issue. I would try test the sensor first. Here is a tutorial on how to test an o2 sensor and how to test wiring:

https://www.2carpros.com/articles/how-to-check-wiring

https://www.2carpros.com/articles/how-to-test-an-oxygen-sensor-02-sensor

After testing let us know the results. Hope this helps and thanks again for using 2CarPros.

Danny-
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Thursday, October 29th, 2020 AT 9:40 PM

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