2000 4Runner P0420 code

[Ilovemytoytota]

HELP!! Getting code P0420 bank 1 on Cali 2000 4Runner Limited. Is it oxygen sensor or catelytic converter? The total vehicle value is almost the cost to replace the catelytic converter. I can afford a oxygen sensor. How can I find out???

[kball]

I would definitely change the sensors before messing with new cats. I think the p0420 is usually the rear O2 sensor but could be either one. If they haven't been changed in a while you might as well do both. Be sure to get Denso sensors, not Bosch.

Find your part numbers here

http://www.densoaftermarket.com/oxygen-sensor.php

and here

http://www.urdusa.com/index.php?cPath=9_13

Then go to Amazon.com and buy them. Best prices around.

[chuckoff]

Other stuff can cause a 420 code. Exhaust leaks are one. Try O2 sensors first. You may be able to go to a muffler shop and get an aftermarket cat. for way less than OE.

[sam333]

How many miles on your cat?

Factory cats last about a 100000 miles as a rule of thumb, but like chuckoff said, other things can cause a 420 code.

The computer compares the front o2 sensor output with the rear o2 sensor output , if the outputs are the same, the computer will throw that code. They should be different. With a good working cat there will be less oxygen at the rear o2 sensor and the signal will have a lower frequency.

Air leaks in the exhaust ahead of the o2 sensors can also cause this, sometime an overly sensitive computer too.

If you have a analog multimeter( with needle) or a digital meter you can backprobe your sensors and time the crosscounts( thats really what the computer is looking at). Crosscounts are the points at which the signal goes from low to high and high to low( think of a sine wave). The service manual will show how to check this.

If you already do your own work on the truck,its not that hard to change the cat. Factory cats are very expensive( they are the best) but you can get an aftermarket one for much cheaper.

If you have a bad cat, be sure you fix any major coolant burning or oil burning problems before you replace it, because it will ruin the new cat and or o2 sensors. Oil burning will take a while , but coolant will damage them in a few miles.

[shemphill]

I get P0420 too on my '99. Mine comes on between 300-400 (after reset) and a couple thousand miles. Sometimes it takes months. It doesn't seem to affect anything like mileage etc. so I just reset it. I have heard the rear sensor frequently goes out and it doesn't really do anything anyway except check the cat.

[sam333]

Originally Posted by shemphill

I get P0420 too on my '99. Mine comes on between 300-400 (after reset) and a couple thousand miles. Sometimes it takes months. It doesn't seem to affect anything like mileage etc. so I just reset it. I have heard the rear sensor frequently goes out and it doesn't really do anything anyway except check the cat.

You are right,its only problem if you need to get smoged, and your check engine light is on or you have a code pending( in alot of states, including california you will fail smog with either of these).