BrianMSmith

ses light just came on, code 420 bad cats. will I be able to pass emissions check in 1 month?

what are my options for new cats? wrecker, aftermarket? what will this cost me?

thanks

Rushin

iTrader: (18)

No. It's probably an O2 sensor.

mike s.

iTrader: (2)

Rushin is right, it could be that your rear O2 is going out, code 420 I believe is for Bank1 (driver side), because code 430 is the same but specified to bank 2, it reads on a scanner like this: 430 - Catalyst System Low Efficiency Bank 2, however I am assuming 420 is for bank 1, although it does not specify, but it would seem logical. Put a new rear O2 in it, and clear the code. If it comes back you probably have a bad cat. My experience has shown me that it is usually a bad O2 if get a HO2S heater or circuit code along with it, if that is the case pay attention to what bank and what sensor it is. If bad cats are the case, you can weld in new ones in place of the old, use good high flow cats though. If patching them is not for you, you can use this setup from random tech, it is expensive but is good quality, and it can be done in your driveway, make sure you got plenty of lube though, here is the link, its the 3rd product from the top. Thunder racing The individual cats are on the catalytic converter tab on the left. Hope that helps.

pozesd99'

iTrader: (3)

02 censor, just get some new ones not expensive at all

sixvi6-camaro

iTrader: (9)

Actually the p0420 code is for the downstream (after the cat O2) so it could be a bad cat or a bad O2. Stock cats are known to go bad on these cars to where GM extended the warranty on the cats for the f-bodies.

My advice instead of just changing O2's blindly. I'd swap the rear O2's (after cat O2s) left to right then clear the codes. If its an O2 the code will follow the Bad O2 and you will get the same code but on the other bank. If its a bad cat you will get the same p0420 code again.

fuseone

maybe its a mixture of both because if it is the cat somthing had to kill the cat

mike s.

iTrader: (2)

True, this code is going to be directly liked to the two O2's downstream of the cats, I believe how it works is that the PCM compares the voltage of sensor 1 to sensor 2 on their respective banks, if it is outside of the acceptable interval of emissions reduction, it sets the code. Both P0420 and p0430 are going to be associated with the downstream O2 sensors. I do not understand why one has no bank specification (P0420), and one has bank 2 specification (P0430). The reason I mention this is because if he is only getting the P0420 code, how will he isolate the offending O2 sensor by swapping rear O2's if P0420 does not specify what bank has the low catalyst efficiency?

davered00ss

iTrader: (4)

Cat's have a 96K warranty on them. But like said, it's probably a bad O2. They are like $50-70. quick 15 min change.

WS6addiction

iTrader: (1)

On my scanner, P0420 = bank 1 sensor 2 catalyst efficiency below threshold.
As I understand it, the PCM switches to open loop, then back to closed loop and measures the difference in the readings from the aft-cat sensors, not the difference between sensors.
I went through this last year with my car. When I pulled the drivers side cat off, it was just an empty shell.

mike s.

iTrader: (2)

Ok then, I guess my older version of HP Tuners did not specify P0420 as bank one, I figured it was though, it seemed logical. What scanner are you using? So it compares readings from open to closed loop off sensor 2? As in the difference between them?

WS6addiction

iTrader: (1)

My scanner is an Actron CP9145. It's kinda old too. I can't do any tuning with it, but it will scan/delete codes and shows real time/freeze frame data. I think some scanners read like yours. If it doesn't specify Bank 2, then it means Bank 1.

After thinking about it some more, you may be right. The PCM tests the cats after certain criteria are met by going into open loop for a few seconds and back to closed loop. I can't remember if it's comparing sensor 1 to sensor 2 while in open loop, or the difference between open and closed loop at sensor 2. Haven't really thought about it since I fixed it.

BlueZ35th

iTrader: (8)

GM sent me a letter.. 120k and i think till 2010 or summ'n. thats for my 02/Z

qwk93ta

iTrader: (13)

This is correct.....I just got a new drivers side cat replaced by GM for free. I had code P0420 and the tech said 90% of the time this code is due to a bad cat.

Rushin

iTrader: (18)

Guys don't make a tree out of a twig... Brian replace both the downstream O2's, since if one goes out, usually the other one will too. If the code stays on, take it to the dealer and tell them to fork over two cats and replace them. At the worst, you've only spent $100 and have some new stuff on the car.

BadGTho

iTrader: (6)

hmm does anyone know the specifics on the cat replacement policy? federal law is like 8yr/80k or something.

Dave 96TA

iTrader: (10)

code 420 is a cat smokin ganja!

mike s.

iTrader: (2)

GM released a service bulletin on the bad cats, I can get it to you if you like, I will bet someone has posted it on here though, so it would be worth a search. I cannot take them up on it since I have headers, and I don't plan on switching it back.

As for making trees, I do have a tendency to over analyze things, a little bit of discussion never hurt anyone. I post here to learn. Replacing the sensors would be correct though, but at $90 a pop I hate to throw sensors at problems. Sometimes a little searching can come up with free diagnostics.

WS6addiction

iTrader: (1)

qwk93ta

iTrader: (13)

P0420 will only get the drivers side cat replaced.....GM will not replace both unless you have two codes, I think the passengerside is P0430. My dealer tried to get both cots replaced for me and GM would not do it.

pitbullmarko

hey guys! i have a problem and cannot figure it out! had the ses light come on and autozone said it was o2 sensors. bank 1 sensor 2 and bank2 sensor 2. i replaced both after cat sensors and the same code came up today! what is the problem?