Well, I'm going to replace ALL my O2 sensors because from time to time I have been getting PO171 and PO430 codes. If the addition of new O2 sensors does not do the trick then one of my cats might be bad.

Please advise me of how many and where the cats are located on my GS400; if anyone has a schematic/diagram please post it up for my reference. Thanks

 

You can always check the owners manual?
In my 2005 manual, there's a diagram w/arrows on page 182 for the GS300 and GS430.

Sorry I don't have a scanner, or I'd toss it up here for you.

Also, for the 2005 GS430, there are three cats. One at the downpipe off each exhaust manifold, and one between the Y's of the exhaust, for a grand total of THREE.

Your results may be different.

 

Yea what roosterjoe said 2 connect to your headers 1 at the ypipe. I see it says you have a borla exhaust you might not have one at your ypipe depending on how far up your exhaust goes.

 

Only (2) cats hooked up to the exhaust manifold and (4) 02 sensors, 2 pre and 2 post. 1 on each manifold and 2 are on the Y pipe.

 

thanks, I'm thinking of doing the "post" (Y-pipe) O2's on my own seem simple enough but I'm thinking the "pre" (Manifold) O2's are going to be a huge PITA so I just might have to pay a shop to do them.

 

They are not that bad. They are right at the bottom of the manifold, a jack and some stand is all you need to get to them.