P0420 after flex pipe change

[jbl]

My Camry 2001 was getting very loud and I asked the dealer to check it out while they fix an ERG valve.

The dealer said the noise is due to the front exhaust pipe which is a whole piece with a cat converter, and wanted $1500. I took the car to Maidas, they said the flex pipe is leaking and have to change the whole thing, they said the flex part is a flex over a pipe and just changing the flex will rattle (??), and offered an after market part include cat for $750. I declined, since I saw various discussion about after market cat throwing CEL.

I then took the car to another national chain and they cut out the flex pipe, and took an aftermarket flex pipe and slipped over the cut and welded it in.

A few days later I got P0420!

Question: is this related to the flex change? Could an after market flex cause P0420?

Thanks!

[JohnGD]

An air leak maybe. Or maybe check the sensor connectors to make sure they are clean and tight.

Just clear the code (code reader or pull the EFI 15A fuse for a minute) and drive for a couple of days and see.

[jbl]

Originally Posted by JohnGD

An air leak maybe. Or maybe check the sensor connectors to make sure they are clean and tight.

Just clear the code (code reader or pull the EFI 15A fuse for a minute) and drive for a couple of days and see.

Thanks!

Air leak from where? Flex pipe looks like a few layers of metal meshes, I assume that can let air in anyway. Is the OEM flex of of different construction? If it is indeed due to flex pipe change, what are my options?

I just cleared the code and will see.

I will check the sensor connections.

[JohnGD]

The wire mesh only protects the steel bellow under it. The exhaust gas won't leak from a good flex pipe. However, the concern is with the welding. Maybe they miss a few places and that allowed air leaks.

It's just too much of a coincidence that the oxygen sensors "go bad" right after repair, which in other normal cases tend to be the problem (instead of a bad converter).

If you or a friend have access to a scanner (like the eBay USB one $20 shipped) then you can also check the oxygen sensor waveforms.

[fenixus]

if it's older than 100k miles then start with replacing this o2 sensor first before anything else. they do not live much longer than that (can loose accuracy much earlier though).

DIY:
DIY : Downstream Oxygen O2 Sensor replacement

find your replacement part here (look for the REAR DOWNSTREAM or POST-CATALYTIC OE style sensor):
http://www.densoaftermarket.com/cata....php?part=o2sn

and buy it on ebay or amazon (search by part number acquired from above link).

[jbl]

Originally Posted by JohnGD

The wire mesh only protects the steel bellow under it. The exhaust gas won't leak from a good flex pipe. However, the concern is with the welding. Maybe they miss a few places and that allowed air leaks.

It's just too much of a coincidence that the oxygen sensors "go bad" right after repair, which in other normal cases tend to be the problem (instead of a bad converter).

If you or a friend have access to a scanner (like the eBay USB one $20 shipped) then you can also check the oxygen sensor waveforms.

They used Bosal flexpipe, similar to this:

http://tinyurl.com/82cnad4

(but charged me $80 for the pipe instead of $12 as show in the link, plus $85 labor)

I hope this is at least a reasonable pipe?

I also feel that it is too much of a coincidence. I may ask they to check their welding if the code comes back (I just cleared it).

[jbl]

Originally Posted by JohnGD

The wire mesh only protects the steel bellow under it. The exhaust gas won't leak from a good flex pipe. However, the concern is with the welding. Maybe they miss a few places and that allowed air leaks.

Is it reasonable to test air leak by blocking the end of muffler and feel around the flex?

[jbl]

Originally Posted by fenixus

if it's older than 100k miles then start with replacing this o2 sensor first before anything else. they do not live much longer than that (can loose accuracy much earlier though).

The car has 120K, still runs very well with plenty of compression (oil changed every 3K probably helped).

Yes may be o2, although if it indeed is, it is kind of too coincidental (right after the flex pipe change).

[fenixus]

well ... it's possible that old worn out sensor gave up when the shop heated the section of exhaust pipe wen cutting the old flex pipe out and then welding the new one in. just saying, it's a possibility.

this o2 sensor is only used for catalytic converter monitoring, hence why it throws P0420 (cat converter inefficient) when it fails.

Originally Posted by jbl

The car has 120K, still runs very well with plenty of compression (oil changed every 3K probably helped).

Yes may be o2, although if it indeed is, it is kind of too coincidental (right after the flex pipe change).