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My P0420 Fix

DanVB1

New member
15
6
3
Buick Ownership
Encore
Had the dreaded P0420 code (catalyst efficiency).
Crawled underneath the car to check for any visual signs and voila! The flex joint on the exhaust pipe from the upstream converter was loose!
Bought a new pipe for about $150, changed the old one and it worked, no more code.
A few notes:
The old pipe is a bear to get off, make sure to support the car properly with a jack stand at the right location (not the floor pan).
Spray the rusted nuts with penetrating oil, let soak a bit. It takes a lot of muscle to loosen them (I strained a rib muscle while pulling the breaker bar).
I luckily found both new gaskets at the O'Reillys, they were cheap. The old gaskets are thin plates, they looked good but probably wouldn't seal well. The new were thicker, sandwich style with a good amount of crush to seal.
The front uses the studs attached to the cat, the rear I used (2) new SS bolts/nuts/washer/lock washer.
I also replaced the downstream oxygen sensor that is screwed into the new pipe. I figured I've gone this far, what's another $70?
So far, so good.
 

Smoothsailer717

Active member
208
42
28
Buick Ownership
2019 Encore
Exhausts are a pain to work on they rust so bad... You usually need pro quality tools to get it done.

What's the year and mileage of your car?

I'm sure u saved $300 doing it yourself. Everything is so expensive now
 

G-277644

Exhausts are a pain to work on they rust so bad... You usually need pro quality tools to get it done.

What's the year and mileage of your car?

I'm sure u saved $300 doing it yourself. Everything is so expensive now
2014, 60,000 miles
The flex bellows was really loose, thats where there was a good size exhaust leak.
I’m lucky none of the studs snapped, a real possibility with this kind of torque to loosen rusted nuts.
I got my pipe from Advance, Rock was about a week delivery time, longer than I could wait.
 

DanVB1

New member
15
6
3
Buick Ownership
Encore
2014, 60,000 miles.
It's not really a difficult job, just tedious and you have to crawl underneath the vehicle.
Having a good assortment of tools helps too.
The risk is snapping one of the studs, so use plenty of penetrating oil to reduce the risk.
Be prepared with gaskets, new fasteners for the rear flange and a new oxygen sensor may be worth the trouble.
______________________________
 

asdx1234

Member
111
6
18
Buick Ownership
2013 Encore
This was changed on my 2013 encore. It had I think like 90k when I bought it. The dealership replaced the flex pipe and O2 sensor so I got lucky and didn't have to mess with that flex pipe.

Guess these cars have the same problems so if someone was looking at a used one they would know what all they are going to need to do to it if they visited this forum.

I see ALOT of these on the road and wonder if that owner has changed the turbo or valve cover/PCV out yet.
 
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