Code p420, but cat was replaced already?!! - Toyota Nation Forum : Toyota Car and Truck Forums

metalmusiclver · 10-26-2010, 10:04 PM

1998 Toyota Corrola 4 door

CEL is on, and it's a P420 code. But the Cat was replaced not even 6 months ago!!!

Advice,suggestions,opinions???

Thank you for viewing, it is very much appriciated!

metalmusiclver · 10-26-2010, 10:19 PM

cat replaced, all o2's replaced. I just read up that a dirty MAF sensor may cause the computer to think the cel is bad. Ill clean the maf element and go from there. I erased the code with my scanner and it takes a few hundred miles to come back on.

adamsautocare · 10-26-2010, 10:21 PM

Could be a bad rear O2 sensor. You can read the O2 sensors for proper sweeping (or lack there of).

Also an exhaust leak can pull in air and trick the rear O2 into thinking there is more oxygen then there really is. (I have this condition right now. stupid donut gasket)

metalmusiclver · 10-26-2010, 10:28 PM

no exhaust leaks, all o2's were replaced

adamsautocare · 10-26-2010, 10:33 PM

Who replaced your cat? Did they replace all gaskets that they removed in the process?

The reason I say this is because you cannot hear my exhaust leak. At WOT, you can get a tiny hint of it but is is very small and not noticeable during daily driving. It takes a couple hundred miles for mine to come on also. I even passed smog with the leak. thats how small it is. Just a thought.

sam333 · 10-27-2010, 11:57 AM

Yeh had the same problem with mine ( bad donut) kept getting 420. It alows air to be sucked into the exhast be fore the first 02 sensor. You could not hear the leak until it was raining and you went over a puddle. I have had to replace the gasket twice in 150000 miles.