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P0420 code

Tiny
JOHNCPEN
  • MEMBER
  • 2001 TOYOTA TUNDRA
  • 3.4L
  • 6 CYL
  • 2WD
  • MANUAL
  • 190,000 MILES
Is there anything I can do to diagnose this myself? Would a more advanced code reader be helpful? I got the code read at the auto parts store.
Monday, November 18th, 2019 AT 8:00 AM

14 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good afternoon.

You need a real scan tool that can read the upstream and downstream O2 sensor readings.

In most cases, the cat converter is the issue. The way to verify it is to monitor the rear sensor. The voltage should be steady. If it varies like the front, then it is the catalytic converter.

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

Roy
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Monday, November 18th, 2019 AT 10:18 AM
Tiny
JOHNCPEN
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O2s11 appears to be steady o2s12 appears to change after vehicle was still warm after a 10 minute shut off and was idling. After driving a few miles they both seem to stay unchanged. What does this tell you? Please see the video.
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Monday, November 18th, 2019 AT 5:12 PM
Tiny
JOHNCPEN
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  • 19 POSTS
Please review and comment on this video. I was attempting to snap test the throttle while watching the oxygen sensors.
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Monday, November 18th, 2019 AT 5:43 PM
Tiny
ASEMASTER6371
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Snap test failed. The bank 2 sensor voltage went from 8 to 0.

You need a catalytic converter.

Roy
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Monday, November 18th, 2019 AT 5:49 PM
Tiny
JOHNCPEN
  • MEMBER
  • 19 POSTS
Do you recommend the Walker that you highlighted above? If I'm not having any drivability issues, what are the consequences of doing nothing? I don't have emissions testing here. Thanks for all your help. P.S. Is this freeze frame information helpful?
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Monday, November 18th, 2019 AT 6:05 PM
Tiny
ASEMASTER6371
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It will not cause any issues except the check engine light yes you can drive it like this.

Roy
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Monday, November 18th, 2019 AT 6:25 PM
Tiny
JOHNCPEN
  • MEMBER
  • 19 POSTS
Can you explain what this info from scan tool means?
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Saturday, November 23rd, 2019 AT 11:49 AM
Tiny
ASEMASTER6371
  • MECHANIC
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It means the rear O2 sensor is switching too much. When that happens, it will set the 420 code. The reading should be constant with very little variation in voltage.

Roy
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Saturday, November 23rd, 2019 AT 1:53 PM
Tiny
JOHNCPEN
  • MEMBER
  • 19 POSTS
Could that be due to the bad catalytic catalytic converter?
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Saturday, November 23rd, 2019 AT 2:19 PM
Tiny
ASEMASTER6371
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As I stated 3 times before, you need a catalytic converter.

Roy
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Saturday, November 23rd, 2019 AT 2:21 PM
Tiny
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I understand that. I was just wondering if the catalytic converter was causing that reading, or if it could be a combination of catalytic converter and bad downstream sensor.
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Saturday, November 23rd, 2019 AT 2:57 PM
Tiny
ASEMASTER6371
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The reading from the sensor is the indication that the catalytic converter has failed. It is not the sensor at all. It is doing its job by sending the reading.

Feel free to ask as many questions as you want.

Roy
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Saturday, November 23rd, 2019 AT 3:01 PM
Tiny
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Thank you!
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Saturday, November 23rd, 2019 AT 3:02 PM
Tiny
ASEMASTER6371
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You are welcome.

Always glad to help.

Roy
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Saturday, November 23rd, 2019 AT 3:03 PM

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