'99 Chevy Blazer, P0420 Code

Robbabob

Well-Known Member
Hey y'all,

I have a video, sideways (sorry), of the live data from my wife's truck with a P0420 code. Reading a few of the threads here, I thought I read one of the sensors should be steady all the time. Looking at the video, all 3 seem to be moving around a lot: .2xx to .8xx. If you would, please view the video on FB and let me know if I'm even looking at the correct codes.

Oddly, after I ran the truck for 5 minutes, 10 minutes later my wife called me out to view a puddle of water under the exhaust pipe. I felt inside and it was damp. She's been driving it a lot today and it's quite cold and windy in Chattanooga. Condensation? It did not smell of coolant.

https://www.facebook.com/photo.php?v=4703538159411&set=vb.1622946527&type=2&theater

Based on what I see, the cat is bad.

1999 Chev Blazer
4.3L Vortec
180K miles
2WD

Let me know what other data should I be looking for or providing to you.

Thanks a ton (in advance).
 

Wooluf1952

Well-Known Member
The link isn't working for me.
Are those O2 sensors the originals?
 
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Robbabob

Robbabob

Well-Known Member
I'm guessing they are originals. Just 3 sensors?

If you have a FB account, you may need to friend me for access. I don't know how else to get a video on here (80+MB). I don't want helpers to have to jump through hoops to help, but I do appreciate the efforts!
 

Wooluf1952

Well-Known Member
From your description, it does sound like the cat is bad, but others will jump in.
IMHO, the condensation puddle is normal and not a problem.
 
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Robbabob

Robbabob

Well-Known Member
Wooluf1952 said:
From your description, it does sound like the cat is bad, but others will jump in.
IMHO, the condensation puddle is normal and not a problem.
I'm guessing just condensation.

Now, I just don't know if the O2 sensor (and which one), or what to check. Oil level if burning too much? It doesn't smoke nor smell of anti-freeze.

Edit: I just want to know if I need to be looking at a Cat change or O2 sensors, I guess.
 

Wooluf1952

Well-Known Member
The O2 sensor down stream of the cat should have a fairly steady reading. If it's jumping up and down like the upstream sensors that would indicate a bad cat.
 
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Robbabob

Robbabob

Well-Known Member
JB100 said:
Goto www.blazerforum.com there is a wealth of info there on the S Series trucks.
Will do, thanks!

Wooluf1952 said:
The O2 sensor down stream of the cat should have a fairly steady reading. If it's jumping up and down like the upstream sensors that would indicate a bad cat.
Yeah, all three are jumping around...
 

dingle

Well-Known Member
Everytime I've had the p0420 its been the cat is bad. I got my replacement for my Honda at advance auto for $153. It was a magnaflow direct replacement. Just an fyi.
 

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