I had the same issues with this code PO420 an after diagnosing the problem.Unless you've tore down these motors ,you'll find out that sometimes it might be a simple fix ,well for me it was .There is a rubber intake hose that that eventually hardens after time an heat an will start to crack an yes the motor will still run but engine light will come on .This intake leak is sneaky because it on the hose an cracks along the seam an you really never see or expect it .You can easily buy one from the dealership .All together its about a 30 minute procedure .After installing the new hose you must have the codes cleared. The intake hose in the States cost about 90.00 dollars This is my wife's Lexus an the last thing I want to hear is ,Theres a engine light on .Believe me when I say Happy Wife Happy Life.!! I hope this helps any Lexus Owners . BTW this is a 2008 Lexus RX400h 3.3
