2005 caravan 3.3 engine .Car showing PO420 code which is [catalyst efficiency below threshold ...bank 1]Relaced upstream O2 sensor no change.Have an autel 419 OBD2 and it shows live data.I can see voltages of O2 sensors as the engine is running.Should the upstrem and downstream voltages be different? The 419 is a good unit as it also gives info as to the possible causes of the code.The only things that I havent replaced is the downstream O2 sensor and the {yikes} cat itself...

 

The upstream sensor should be switching rapidly between rich and lean. Downstream should show very little change. If the downstream is switching almost as rapidly as upstream, it's a sign the cat converter is shot.

 

................yes the downstream O2 sensor is switching rapidly and reading mostly in the .7 volts area. Gonna try some cat cleaner you put in the gas tank....for $20 its worth a try......Its made by PRESTOLITE {Pep - Boys sell it in U.S.A}.I got some in Canadian Tire....

 

These additive are only good for 2 person. The guy who made them, and the guy who sells them.

Here is a trick that may revive the Cat. It is called an Italian Tune up. Pull off one of your spark plug wire, and hold the throttle at 1.5-2K RPM for 15 minute, and watch your Cat glow red hot due to the excessive fuel from the sparkless cylinder.






Just joking!!! don't do that.

Find a Muffler shop that would cut and weld on an aftermarket universal Cat Converter, it isn't really that expensive.