ssbogger

So I got a code reading P0420 Catalyst System Efficiency Below Threshold (Bank 1)

I read that I might have to replace the cat. Well Im pretty sure i have two so which one is it? Also I read that someone put in a new o2 sensor. I did this about a year ago so i wouldnt think that this would be the problem. If it was the problem woulnt it have given me one of the many o2 sensor codes?

Thanks.

blink

its gonna be the first one(bank 1), and if your cali speced runner is like my taco, itll be attached to the down pipe. Youll either have to order the entire downpipe + cat from toyota or have an aftermarket one welded into place. hope this helps

ssbogger

I didnt think my runner was cali-speced. What makes you think so?

kevin444

As far as i know only cali speced runner have 2 cats. Otherwise there would only be one. In regards of your other post about hi flow cats leave them alone stick with the stockies they retain the backpressure you need. As far as for a 99" Model i wouldnt think the cat would die out that fast make sure those 0 2 sensors are doing well first =)

Unhappy99

Under Federal law, the cat is warranted for 8 years or 80K miles. And yes, 0420 codes have been know to be caused by bad 02 sensors. Usually the after cat sensor, since that's the one which detects whether or not the cat is functional.

ssbogger

Ok well i replaced my o2 sensor less than a year ago. The car has 110k on it so im guessing that it could go bad in that amount of time. As far as sticking with a stock one, they are too expensive.

blink

are you sure it wasnt the first o2 sensor you replaced before? that sensor is know as the air/fuel and thats the one that costs 250. the second o2 senor is much much cheaper. easiest way is to hook up a voltmeter or use a scan tool to see if that sensor is working correctly

ssbogger

Im not really sure what sensor it was but it was the one that 90% of the people replace. I know one of the sensors goes out more often than the other, thats the one i replaced.

Now for another question... If my exhaust pipe was cut in half between the first and second catalytic convertors, could this cause the code? Someone tried to steal my cat and must have gotten spooked b/c they only got halfway done.

joey_hooker

ok i got the code!! the p0420 and by now i have replaced both o2 maf sensor cleaned intake throttle body and replaced the cat. and im still getting the check engine light i have done eveything the idiots at the dealership told me to do ( not that autozone couldnt have told me the same for free), so what else do i do now,

jonnydclark

Note: This is a really old thread. Sometimes its better to start a new one than resurrect one.

If you have replaced both O2 sensors have you double checked that the computer can see them and they are functioning. You can watch them with any decent scan tool and they will cycle in a range between -0.5v and 0.5v. If they are tracking in a reasonable manner when you watch them and you still get cat below threshold you probably actually need a new cat. The question then is what caused it to go bad. Do you have something causing incorrect fuel to air mixture? Did you drive for a long time with one of the O2 sensors not working?

I had a maxima that had a IAC valve issue due to a bad connection in the wire harness. It kept trying to "warm up the engine" with rich mixture and high idle rpm. It was like that when I bought it so no telling how long it was run that way but I had to change both cats before I could get it to clear all the codes / monitors.

Sameera1978

Wow, had no idea the cali speced 4rnrs checked to see if the cat is doing its job. Found myself sort of wondering at first because mine doesn't even have a cat, just two mufflers, and I never get a CEL for it. I pop my scanner on regularly and everything passes the check list. I don't live near cali though.

As far as the question at hand, I would check to make sure the sensors are working properly, if so then start checking stuff under the hood. I can't really say what the 4rnr has for "smog control" but that sounds like it would be my next stop on the list.