Have the EML on on my GS450h, read the fault codes and I have 2 fault codes that are identical (P0430). I cleared the fault codes and it stays off for a day, then as soon as I go above 60mph the next day, it comes back on again, the faults are stored and not current codes. I've not noticed any MPG loss or loss of power whatsoever! So am I safe to assume its not the catalysts? Only other thing I could think of is an o2 sensor gone bad perhaps? I don't want to spend money really as I'm about to sell the car for a more economical one for my 150miles per day commute to work! Just had all 4 wheels refurbished too which set me back a fair amount, now this! AAAAARRRGGGG!

Did a quick search but nothing that seemed to be of any help!

Any ideas or experiences/fix stories of this fault?

 

Take it to an exhaust shop and see if you have corrosion.

If you're a DIY person:


In a gist, your inlet (before cats) is suppose to be cooler than the outlet.

Great tutorial to tell you which is broken, and whether or not you'll want to buy new cats or not.

GL!

 

did you end up fixing this issue? if yes, how? did you replace one cat or both?
or was it oxygen sensors?
i have the same issue on my 2006 GS430..