'99 Chevy Blazer, P0420 Code

Robbabob

Original poster
Member
Dec 10, 2012
1,096
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

Member
Nov 20, 2011
2,663
Milwaukee, Wisconsin
The link isn't working for me.
Are those O2 sensors the originals?
 

Robbabob

Original poster
Member
Dec 10, 2012
1,096
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

Member
Nov 20, 2011
2,663
Milwaukee, Wisconsin
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.
 

Robbabob

Original poster
Member
Dec 10, 2012
1,096
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

Member
Nov 20, 2011
2,663
Milwaukee, Wisconsin
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.
 

Robbabob

Original poster
Member
Dec 10, 2012
1,096
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

Member
May 26, 2012
59
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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