my check engine light is on what is the problem? on 1996 Toyota Land Cruiser

i used a hand held diagnostic machine to check it and the code that came back was PO420. please get back to me asap

2 answers 1 comment
Use a scanner that can provide you with rear O2 sensor readings. If you have a smart phone there is a wonderfull new piece of equipment for $99.99 that can provide you with this info. Go to www.plxkiwi.com to see. I really can't believe how good the device is. Of course it comes from silicon valley.
The truck is 16 years old. You most likely have to replace the cats.
P0420 is low catalytic converter efficiency.Could be a bad cat, false O2 sensor readings or have failed due to an out of tune engine/excess fuel or misfire.
thanks again,what are you suggestion first?