P0420 code on 2006 4 cylinder 126,xxx miles exhaust manifold replacement due to crack - Pontiac G6 Forum
 
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post #1 of 1 (permalink) Old 05-30-2016, 01:03 PM Thread Starter
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P0420 code on 2006 4 cylinder 126,xxx miles exhaust manifold replacement due to crack

2006 4 cylinder 126,xxx miles exhaust manifold replacement due to crack

The car was getting a P0420 code. It drove and ran fine.
Read up on the internet, many things cause this code.
Should have pulled the heat shield ( three 1/2 bolts) first.
Checked the temperature after the cat with a heat gun. It was grater than before the cat.
Bought a harbor freight scanner ( 60694) so I could see the oxygen sender data.
Things looked ok but the code would come back even after being cleared.
Changed the thermostat because the gauge would not move some mornings. Found the inner rubber seal on the factory thermostat out of place on half of it. Spring time.
Still got the P0420 code.
Started to replace the oxygen sensors due to them being the originals and 126,000 miles. Pulled the heat shield from the top. Three 1/2" bolts, 3/8 ratchet worked fine. Under the heat shield was a very visible crack with a small hole, between the runners in the middle on the top. After removing the manifold the crack was not on the bottom. If you want to try welding up the crack, mine was only on the top.
To disassemble / clean it took me an hour and a half. I also have a car lift. It took an hour to reassemble.
Tools needed for the nuts to the head.
-short 1/2" 6-point 1/2"drive socket
-1/2 drive extension 5"long
1/2' ratchet
Oxygen sensor tools:
7/8 or 22mm oxygen sensor socket and open end wrench.
Under side of manifold support bolt (easier with oxygen sensor removed) tools:
15 mm 3/8 drive socket
3/8 drive extension 3" long
Red Scotch bright pad for cleaning gasket surface at head (I used a shower shaving mirror to see the head.)
Under the car exhaust flange tools:
1/2" 6 point socket 3/8 drive
3/8 extension with ball end from harbor freight 9" long
3/8 straight extension 9" long
Paint scraper and wire brush for cleaning gasket at the exhaust pipe flange.

I started with a short drive to warm things up.
Then from below I removed the oxygen sensor.
Next the three nuts at the flange. I broke one off and the other two the whole stud backed off.
Up top I removed the oxygen sensor and the support bolt (15 mm) below it.
Remove the Ten 1/2" nuts at the head.
Remove the manifold thru the top.
Remove the manifold gasket and clean the head with red scotch bright pad.
Use a paint scraper to remove most of the pipe gasket then a wire brush to finish it off.
***My 15 mm bolt did not want to thread in, check this while the manifold was out of the car.
I installed the gasket then the three new studs that came with my new manifold/converter. This way when I installed the manifold into the car I could slide it on the exhaust pipe flange at the same time.
Install support bolt loosely then install the ten 1/2 nuts loosely. (One nut had some interference between the socket and the manifold, shifting the manifold made it fit better.)
Tork 1/2 nuts to 124 inch pounds
Tighten the 15 mm support bolt -17 foot pounds
Install oxygen sensor hook up wires.
Install heat shield 1/2" bolts- 17 foot pounds
From below tighten the three 1/2" nuts from the manifold to pipe.
Install oxygen sensor hook up wires.
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