Code P420

Ok, so I replaced my upstream o2 sensor due to the P1135 code. Everything was fine for about 50 miles then the light came back on. Went to AutoZone and their code reader says now the code is P420. P420 could be:

catalyst system efficiency below threshold - bank 1. Probable cause:

air leak in exhaust before rear heated oxygen sensor - bank 1
AF sensor error
fuel system fault
faulty catalytic converter

When I replaced the front sensor, the tip was white with no carbon build-up which indicates a lean condition. FYI, I've done the air box mod.

Where to start? Thanks

 

where to start.?
this is the google search on the code.
http://www.obd-codes.com/p0420

now this is why you should replace both o2 sensors at the same time.
and please, use only DENSO sensors.
I have been posting this, you should replace both at the same time, because they both work together with the cars computer, and now you have a new one working very well, in front, and the back one, which was getting old is now not as efficient as the front one.

 

You can also test your o2 sensor with a volt meter to check if its dead. And dying o2 sensors can be tested with a oscilloscope or scope meter.

 

I used a Denso from RockAuto. BTW.. the truck has 308,800 miles on it. I'll probably go ahead and order the rear sensor today.

 

well no more than they cost, and how long they last, and they CONTROL how efficient you motor runs, keep them in good shape and your cats will last longer. but do what you want, but I am almost 50 years old, and I have never replaced a cat or had a problem with one in my life. here was the old ones I replaced on my truck, no cel, but with the new ones she ran so much better and got better MPG, and thats less going out the tailpipe and less work on the cats.
and these were the worst I have ever replaced on a vehicle, this is also the results of running with a poor tune.

 

and if you have a lean condition, you should really look at fuel filters,
a lean condition can really blow up your cats, and motor.

 

Just a bit of side information, the post-cat sensor has nothing to do with how the engine operates. The post cat sensor has one job, and one job only, to measure the efficiency of the catalytic converter. I am currently working on a major write up on the Toyota P0420 code, and everything involved in it. Hopefully I will have it up soon, and it will get a sticky. lol.

 

sorry about that I was think bout something else with the lean thing.... had the ball and chain nagging me and the nag-in-law calling since we had a deluge last nite and someone has some water in basement....
just try to remember this, its not wasting money to throw in a new set of spark plugs every 25,000 miles, and monitor other components.
and small investment in time and parts will save gas and money on major repairs. and a lot of gas. i have a lead foot, I love to race cars, love a count down at a red light, but besides the basic tune, the best thing i did was the new o2 sensors, and I still am hitting 21 mpg in 70% city driving.
(I am white trash, I don't like to use my air, i like windows down, matter of fact had a rude bit%$ who tried to cut me off call me that the other day!)

 

While it is of course your choice, there really is no need these days to replace the plugs every 25k miles. Especially the new iridium tips. The platinum and iridium plugs are too expensive to replace that often.

 

yeah I know but the was no matter what you do if you leave them in for years they can get stuck, and I don't want that to happen. it usually only happens to me anyway............ and I just like spending the time looking over the motor while doing it.

ford does do some dumb things with plugs.... remember the blow out problem with the modular motors. they were putting short thread plugs in and they were then trying to tell people to use blue loctite to keep them in.

 

Need to replace my rear O2 sensor. Haven't got hold of a manual yet but it looks like the wires go up under the passenger seat. Do you have to pull the seat to get at the connector? (California truck, if that makes a difference)

 

You have to take the lower trim off the door frame and pull the carpet back.

 

http://www.tacomaworld.com/forum/1st-gen-tacomas/142451-rear-o2-sensor-done.html

 

Have you checked for:
air leak in exhaust before rear heated oxygen sensor - bank 1
AF sensor error
fuel system fault
faulty catalytic converter?

Just kidding! But seriously, if you want to check for an exhaust leak, shoot some compressed air or shop vac air into the tailpipe plug the air intake and spray some soapy water on the exhaust system. It will foam up around any leaks. Cracked exhaust manifolds occur a lot on 5vzfe unfortunately.

You could run some fuel system cleaner like sea foam. It could help unless you have a bad component somewhere in your fuel system.

A bad seal on the gas cap will cause an error code. Don't remember if its 0420 or something else... too lazy to search for it.

Do you have rough idle or does it run badly?

 

I had a P0420 in our old 00 4Runner that wouldn't go away after replacing both sensors, cleaning the air flow sensor, checking for vacuum leaks, checking for exhaust leaks, etc. After all that and with over 200k I suspected the cat was going but lucky me it was a California spec truck (originally sold in NH too) and the converter was pretty pricey. The truck ran fine so I made a spacer for the rear 02 sensor out of the flange from the original sensor. I cut the sensor out and basically had just a flat plate. Spacing the sensor that extra 1/4" out of the exhaust stream did the trick. Light never came on again and although we no longer own it the rig now has 227k on it and it's still out.

 

while that eliminates the CEL from coming on, it doesn't actually fix the problem....just sayin.

 

Just fixed my code, turned out the previous owner gutted out the cat

 

Yes I know that. But it fixed the problem of the light coming on and the truck ran perfectly. There aren't any tailpipe tests here only and OBD2 check so it's still passing smog with flying colors! It was a free fix that's a lot more reliable than most of the aftermarket catalytic converters I would have installed to fix it correctly.

 

Does anyone know the part numbers for the 2 oxygen sensors to a 96 2.7l? I have this same code and want to fix it cause I have to smog it soon. I'm pretty sure I have an exhaust leak too.