P0420 and p0430
 

Po 420- 430 is "Catalyst system efficiency below threshold" right and left cats.

Those codes come up all the time on OBDII toyotas( problem or not).

You have four 02 sensors on this engine one ahead of each cat and one behind. The o2 sensors ahead of the cats "read" the amount of o2 in the exhaust stream ( low o2 rich , high o2 lean ) and send a signal to the computer, based on that, the computer adjusts the on time for your injectors( longer for a lean signal and shorter for a rich signal).

What the computer is trying to do is get the best air/fuel ratio (about 15:1) for the cleanest emmisions.

Then the exhaust goes through your cats and is cleaded up( HC, CO and NoX ( bad stuff) are burned). Then out passed your second o2 sensor. If the computer does not see a lower oxygen level/ different wave form( cleaner emmisions) on the second o2 sensor compaired to the first, it sends the 420 -430 codes.

This is telling you that your cat is not working well enough or at all. The problem is, its not always the cats( not usually ). It can be a bad front or rear o2 sensor, air leaking into the exhaust causing false 02 readings, or nothing. Most of the time if you erase those codes they will not come back or come back a few times only.

The real test for your cat and o2 sensors is if you pass smog.

The cat and second o2 sensor have no affect on the way the engine runs, they are for emmisions only. The only bad thing is, you cant pass smog if your CEL is on, and if your cats really are not working well, then you are polluting the air.