Yet another P0420 thread [Archive] - GrandAmGT.com Forum

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slownlow43
03-03-2013, 12:19 PM
A little backstory. I just purchased a 2001 GAGT, 142,XXX miles, with a little front end damage from an insurance auction. As soon I started it to drive it home the SES light was on. Had it scanned and only P0420 showed up. I've only got two real symptoms.

1. SES light (duh)
2. Occasional rhythmic pulsating while driving on the highway. I haven't had a chance to set the cruise and see if it does it then/disables the cruise.

I've looked at the front O2 sensor and catalytic converter and both appear to be in very good condition, like they have recently been replaced.

So my question is this; what else could cause this code to be thrown? It runs great. I currently have a 99 3.4 Alero that the GAGT would eat for breakfast. Any ideas or input so I can avoid just throwing money at it?

1995quad4se
03-03-2013, 02:58 PM
Every single car I saw with a P0420 in my time at a used car dealer needed a cat. THe old one was probably replaced with a cheap garbage cat because they thought they would save some money.

slownlow43
03-03-2013, 05:33 PM
Every single car I saw with a P0420 in my time at a used car dealer needed a cat. THe old one was probably replaced with a cheap garbage cat because they thought they would save some money.

If this is the case, at least the bolts should be easy to remove...

Metalxen
03-05-2013, 11:41 AM
there are two sensors and that code says there is a problem with the post cat sensor

Metallman56
03-05-2013, 01:47 PM
Every single car I saw with a P0420 in my time at a used car dealer needed a cat. THe old one was probably replaced with a cheap garbage cat because they thought they would save some money.

i have the same code, and have had it on sense i put on my borla cat back system. just an fyi

[ChaosweaveR]
03-05-2013, 02:14 PM
Bad cat, replace with a high quality aftermarket or OEM cat.

/thread

slownlow43
03-06-2013, 04:58 AM
Searching on here says the Magnaflow converter is the cheapest option to not throw a code. Can anyone confirm/deny? Link to said converter:

http://stores.channeladvisor.com/DotComParts/Items/mag23520?&caSKU=mag23520&caTitle=Magnaflow%2023520%20-%20Direct%20Fit%20Catalytic%20Converter

slownlow43
03-06-2013, 07:58 PM
I've done some research and it appears that I can put a resistor on the signal wire of the O2 sensor to simulate a good reading.

http://www.automotiveforums.com/t672110-oxygen_sensor_99_grand_am__testing_and_replacement .html

According to that link the normal operating signal range is 3-10 ohms. So if I put a 5 ohm resistor on the signal wire it should simulate a good reading. Does that sound about right to everybody else?

unchained_01
03-07-2013, 01:52 PM
Seriously bite the bullet and get a high quality Cat
Save your self so money in the long run

Metalxen
03-08-2013, 01:02 PM
I have a Magnaflow high flow converter and that set off the code. Here is a link to an o2 emulator that a few people i know have on their cars.http://shop.zzperformance.com/store/p/468-O2-Emulator.aspx