2006 Highlander P0420

2006 Highlander, 4Cyl, 110,000 miles, new plugs, new air filter. Code P0420 reset several times comes back. Read a lot from some knowledgeable people seems code is not defined as replace cat. I don't mind sending it to dealer for better tests than my scan tool, I just want to know what to ask for. I don't want to replace the O2 sensors since at that point costs add up.

Tires have proper air pressure, gas tank is full, and windows are up.

Thanks for any help

The Plan

I read as much as I could on what was posted out on the wild web. I think I read the Pre O2 sensor controls the engine, and the post O2 sensor monitors the cat.

Since the code is ambiguous at best I am going to replace the post O2 sensor as soon as I can get my daughter to bring the car by. Also it seems my scanner does a little more than clear codes so I will read the data it holds when the code comes in.

As soon as I do it I will post back the results in a few days

HO2 sensor is very often the problem. Good luck.

Today I got my daughter to come by so I could change out the Post O2 sensor, she was two weeks behind in her laundry.

I also scanned first and the following set when code happened
Fuel Sys1 CL
Fuel Sys2 NA
Calc Load% 49.8
ECT F 187
STFT B1% 3.1
LTFT B1% 0.0
Eng RPM 1748
Vec Mph 39
Spark Adv 33.0
IAT Degree F 82
MAF Lbs/Min 1,0
TPS% 19.6

Honestly I cant tell you what most of it means but if O2 sensor doesn't cure it I will be learning. I will post again what happens. Hard to get college students to talk to except when payments are due.

Also, if the HO2 sensor doesn't solve the problem, check for leaks in the exhaust system between the engine and the cat converter (loose connection, rusted area, or burned out seal)