by kulkarni_ash, December 4, 2006
kulkarni_ash
Hi
i have a toyota corolla 2001 with 135,000 miles on it..
I have replaced pre oxygen sensor and MAF sensor in May, now i am getting error code PO420.
I have added fuel addetives to get the fuel filter cleaning.
what else can i do, do i have to change post O2 sensor or catalyst converter.
how can i debug the exact cause..
Ashish
Bikeman982
Hii have a toyota corolla 2001 with 135,000 miles on it..
I have replaced pre oxygen sensor and MAF sensor in May, now i am getting error code PO420.
I have added fuel addetives to get the fuel filter cleaning.
what else can i do, do i have to change post O2 sensor or catalyst converter.
how can i debug the exact cause..
Ashish
Did you have the code before you changed those items?
Have you reset the code and waited to see if it came back?
Exact cause cannot normally be determined by the code, just a general system malfunction that would have to be troubleshot. Usually dealers will change the most expensive part and charge you a lot for it. Then they reset the code and wait to see if it comes back, if it does they change the next expensive part. It is kind of a racket for the emission system and the dealers.
P0420 code is something that you see often on the 8th gen Corollas - unfortunantly, there is no single component that seems to be more at fault than others. Basically - you will have to examine the entire EVAP system, which can be quite complex and take a good portion of your time. It is within the reach of a DIY - but you will need the factory service manual, some specialized equipment, and atleast a few hours to do the complete test.
I would check the parts instead of just blindly swap parts. You could do that - but many times you will tend to overlook the underlying problem end up replacing good components.
Just do a search for that particular code or EVAP issues, especially on this forum, will turn up a ton of info that might be useful.
Bikeman982
A lot of people have had the same malfunction code and have done various part and cleanings to eventually get it repaired.
Just a shot in the dark - would a bad fuel tank cap cause this code to come up? Might be as simple as that?...
Sure can - either the cap was too loose (didn't tighten until the cap clicks, or the gasket on the inside is bad).
Most shops will tell you the first time around that it might be a bad gas cap or you didn't tighten it enough. If the code keeps coming back - then it is more likely multiple issues that are causing the code.
friendly_jacek
Found by googling:
Bikeman982
Found by googling:http://www.aa1car.com/library/p0420_dtc.htm
Looks like a very useful site.
i've had this code for about a year now on my '01 CE. First time it came up, i (foolishly) replaced the front 02 sensor thinking that was at fault. Second time it came up, i cleared the code and thought it was just bad gas or something. Third time it came up, i had a trusted shop tell me my cat was dying so i chose to take the car to the dealership (i hate all dealerships BTW).
This past friday i took the car in and sure enough they said the cat needed replacing, to the tune of $1,700. Luckily the car is still under warranty for emissions so they fixed it at no charge to me. Hopefully this doesn't come back or back to the dealership it goes (as much as that pains me).
i've had this code for about a year now on my '01 CE. First time it came up, i (foolishly) replaced the front 02 sensor thinking that was at fault. Second time it came up, i cleared the code and thought it was just bad gas or something. Third time it came up, i had a trusted shop tell me my cat was dying so i chose to take the car to the dealership (i hate all dealerships BTW).
This past friday i took the car in and sure enough they said the cat needed replacing, to the tune of $1,700. Luckily the car is still under warranty for emissions so they fixed it at no charge to me. Hopefully this doesn't come back or back to the dealership it goes (as much as that pains me).
Email mei also have a 01 corolla ce. i have had this same problem as you, i now have 237 k on my car. did your light come on after replaceing your cad converter? ps i have had this problem since 150 k and now just replaced my engine with a high quality remanufactured long block as i was burning oil ( no smoke) since 200 k. runs like new now however light 420 came back 
Email mei also have a 01 corolla ce. i have had this same problem as you, i now have 237 k on my car. did your light come on after replaceing your cad converter? ps i have had this problem since 150 k and now just replaced my engine with a high quality remanufactured long block as i was burning oil ( no smoke) since 200 k. runs like new now however light 420 came back
My longstanding P0420 disappeared after the dealer replaced the cat under the fed. emissions warranty. Don't know if it was something before the cat that caused it to go bad, but this was several years ago and no problems with that code since.
Hi
i have a toyota corolla 2001 with 135,000 miles on it..
I have replaced pre oxygen sensor and MAF sensor in May, now i am getting error code PO420.
I have added fuel addetives to get the fuel filter cleaning.
what else can i do, do i have to change post O2 sensor or catalyst converter.
how can i debug the exact cause..
Ashish
My Hanes repair manual which covers that model year lists it with the very generic sounding "Catalyst System Fault." Not very helpful huh? On diagnosing cat issues, they give very little info other than visually inspecting for proper exhaust pipe mating flanges and bolts for loose bolts or flange leaks; inspect for dents or damage to the cat protector; and to inspect heat insulator for damage and check for adequate clearance between insulator and cat. Then the manual just gives a very short how-to on replacing the cat (doesn't sound cheap or like a lot of fun). Where your car, like mine, is long out of warranty,I wouldn't replace it unless I was certain that that is what's throwing the code.
-Spyder
Topic List: Go to Toyota Corolla, Chevy Prizm (1998-2008)
