Originally Posted by Warwicke36

Hi All,

A little background from me. I am an ASE certified tech of 16 years. I just picked up a 2004 4Runner v6 to have a little fun with on the cheap. I decided to give it a few weeks of driving to give it a proper shakedown and see what it needs to get back up to snuff before I dump some money into fun things.

I am glad I did because after my first longer drive (I work 3 miles from home)...I came back to the shop with P0420 and P0430 codes.

Shame on me. I did scan it at the shop prior to purchase but in my haste I did not check to see if monitors had run. I am fairly convinced the PO cleared the codes and knew I wouldn't likely complete a drive cycle on my road test. He was right.

So here we are. I have codes for both converters on a Cali emission car. Great.

Not 100% convinced I needed cats, or knowing how long this problem existed prior to my purchase. I decided to put 2 downstream O2 sensors in and see what happens. They looked old, old enough to be original. So I swapped them out. I was happy as at first the CEL stayed off. But within a day or 2 it was back. Frustrated I started researching CARB compliant Catalytic converters for the car. Not shockingly I was unhappy with the cost.

Upon installation of the O2 sensors I did notice the flange for the Cat was rusty and potentially leaking, even if just slightly and not enough to make the vehicle loud or smell exhaust in the cabin.

If you've been reading waiting for the fix portion here it is

I got a gasket that goes between the cat and y-pipe for each side.

a little heat to the nuts and it all came apart easily. Once apart it was clear how smoked the old gasket were! The driver's side didn't look all that bad before taking it apart.

I replaced the gaskets and drove the vehicle for 2 full drive cycles. So far so good. I did check the monitors and and catalyst monitors did pass. So fingers crossed that it doesn't come back but I hope this post help anyone struggling with Catalytic Converter efficiency codes.

If anyone has these codes I highly recommend checking the conditions of these flanges/gaskets. The proximity of the sensors to the flanges makes it easy for intrusive air to affect the readings.

Cheers,

Pics below