Steve8S

As the thread title says, my 2001 T/A is throwing the code "P0420 Catalyst System Efficiency Below Threshold (Bank 1)" I have replaced the cat on the drivers side (bank 1) and reset the code. However, the next day the same code was displayed. I reset the code thinking it may have just been in memory, and the next day, same thing. The O2 sensors seem to be functioning properly from what I see on the Tech 2 scanner and HP Tuners. Any help at all is appreciated.

98TAjwh

iTrader: (4)

i had the same code show up and it turned out my O2 sensors were bad. if you replace the cats already and the code won't go away that may be your problem. how many miles on the odometer? i ask cuz most O2s are only good for 100k tops.

blackfang

iTrader: (2)

It very well could be the o2 sensors.

Steve8S

It has 95,xxx miles on it. I was thinking if any of the O2's #2(post-cat) would be the place to start?

Tuffguy610

iTrader: (2)

I would suspect that O2 sensors are a great place to start. I'd rather buy one or two $50 O2 sensors than replace a cat. Of course, you could always get that code tuned out by a local tuner. I am fighting with the P0420 code in my beater (3.8 H-body), and I have just learned to live with it except for inspection when I reset the computer and run the car less than 50 miles so that it tests all readiness monitors except the cats (we can get by with 2 unregistered readiness monitors in PA). Then after 50 miles my code comes back on and the eternal check engine light reigns forever....

Steve8S

I can tune the light out myself, but that is not what I want to do. I would rather fix the problem than forget about it.

2xLS1

iTrader: (25)

Was it replaced with a GM cat or aftermarker. If aftermarket they can still set cat codes.

blackws6ta

iTrader: (1)

make sure the replacement cat has the same sized element as the stock one. If you replaced it with a GM cat that your problem lies in the o2's Use tech-2 to datastream the o2 switching and voltage. THe front o2's should switch frequently and fast and the voltage should follow. The rears are lazy and should make more of a sweeping line effect. If any of them are flat lined or not switching at their rate. replace them. The rear o2's are the 0420 code tattle tales. They are usually the ones. Anything past that, you could be looking into gasket leaks in the motor / vacuum leaks and so on.

dancrosoft

I would replace that downstream O2... I just had my CAT replaced for the same issue and it went away (but I changed both downstream O2s before hand..)

I bought the BWD Universal O2 sensor for downstream. They are cheap and have lifetime warranty . No problems at all so far and the wiring is really easy ....

http://www.oreillyauto.com/EW3/Produ...&currentPage=1

http://www.bwdbrand.com/Online%20%20...g/Content.aspx