I have a P0430 code on my 2007 GS350 and I wanted to see what's the best way to diagnose the issue. The car is running fine. I am thinking it's either the o2 sensors, exhaust leak or a clogged cat.

I'm not sure if I should first try the cleaner, test the o2 sensor. or take it to muffler shop to see if there is a leak.

Any suggestions?

 

Buy a new Lexus gas cap on EBay before you do anything else.

 

I have a new gas cap I recently bought. I checked the gas cap and it looks fine.

 

Mix dish soap with water and, with car on, start spraying exhaust pipes--start with the 'Y' pipe--. You'll notice bubbles if u have a leak.
Is the car louder than normal?

 

Ok, I will try spraying and see if I can find any leaks. Car drives and sounds normal.