May 2011, there was a posting on the dreaded P0420 bad cat efficiency issue. I reported that my 2002 Sienna had popped that code after running down hill 17 miles on engine braking, on the cuota to Orizaba. There was a lot of discussion on the recommendation by Scotty, Houston radio car talk host, to put chemicals in your gas tank.
Later, my code went away. Several people said it would soon be back.
Last week, around 17,000 miles later, I got the P0420 code on the same trip, but before I entered the high speed highway. I erased the code, expecting it to come right back on, but so far, nothing, and I did the 17 mile down hill run, but not with engine braking.
Someone recently said on a posting that almost always the P0420 code is a bad cat. But, in the past, when I have Googled extensively, most mechanics insist it is usually bad sensors.
The way I see it, it’s one of several things.
Engine pumping something messing up the cat, that eventually burns off. It does not seem to use much oil.
Or, bad cat. Because it seems to come and go, bad cat seems less than sure.
I would rather identify the real problem, than toss expensive parts at it. Which is the point of this posting.
I bought what I thought was a good scanner a year or two ago. I got an EQUUS 3140, partly so I can run older cars so often found here in Mexico.
It promises freeze frame; and live sensor data. But, sensor data is digital, and bounces all over the place, making it nearly useless for telling me if a sensor is good. Unless someone can give me ideas how to better use it.
Now, people have posted one needs to look at sensor output with a scope. So, how do I do that? Does this mean a new scanner with built-in sensor scope, or a separate scope, and if so how does one hook it up to the car? I think I can pay for a pretty good scanner/scope if I avoid one needless cat replacement, and then have it forever.
Any help appreciated.