Originally Posted by senor perfecto

Long story short/long…

For the past several months I have been trying to diagnose and repair what had been told to me was “99% of the time” a bad catalytic converter on my 2002 SR5 Sport.

A few years back, the car Failed California smog test. Mechanic immediately said replace the cat, you’ve got 200k on the car, it’s time. I waited and took… alternate routes to getting the car roadworthy. Alternate and pricey. This year I decided to actually fix the issue, knowing a new cat would run me thousands of dollars.

I started as small as I could. Cataclean. It appeared to do nothing. I bought the denso O2 and fuel air sensor and had a mechanic install them. More cataclean. List of laborious drive cycles. Check engine light kept coming on after reset, so I knew the sensors were ok and I just spent $275 on nothing.

An interesting thing happened at this point:

CEL on
P0420 code
P1130 code (new!)
P0171 code (new!)

It looked like my brand new denso O2 sensor had gone kaput in under 3 weeks! Not bloody likely but what can you do?

So I take it to a new mechanic. Friend of a friend. He says he needs to start all over from the beginning with a diagnostic. Which reveals a bad mass airflow sensor. He orders one and replaces it and tells me to drive around and see what happens. Meanwhile I am thinking GREAT I’m going to waste another tank of $6/gallon gas completing this insane drive cycle and the CEL is going to come back on and I’m still going to need a new cat.

But a miracle happens. I drive only about 30 miles at 55mph and the cat reads AVAILABLE/COMPLETE for the first time in years. I literally do t believe my eyes as I call the mechanic and he says bring it in I’ll smog it. I bring it right in, and pass smog.

Take from this what you will. Just one anecdote. But EVERYONE (including me after reading countless posts on here) was sure it was the cat, and it would have been upwards of $3k to replace. And finally $200 and a knowledgeable, legit mechanic later, everything is great.

Thank you to all who continue to share your info here. You know a lot more than me.