Bad cat code P0420 low efficiency

[jlawlor]

I have replaced the after cat O2 sensor and continue to receive this code. The code is intermittant. After clearing the code I can run highway for about 500 miles before it returns. Mixed commuting milage will only go about 150 miles. The sensor has carbon on it when removed. The car runs fine and has 110K miles. I get no other codes indicating too rich or lean mixtures. Should I try injector cleaners? Will these cleaners also work on the cat? Is it worth trying to remove and rinse out the cat with solvent to improve efficiency? Can one buy a used cat from a junk yard or is this against some laws?

[Legacy777]

If you're continuing to get the code, and have replaced the sensor. The problem more then likely is either in the wiring or that the cat is truly not working as well as it's supposed to.

 

You don't want to clean it with solvents. They make cleaners you can buy and dump in your tank that's supposed to help, but I don't know how well they'll work.

 

If you can find seafoam, give that a shot www.seafoamsales.com

[jlawlor]

I'll try the seafoam tonight if I can pick up a can and report back. Thank you.

If you're continuing to get the code, and have replaced the sensor. The problem more then likely is either in the wiring or that the cat is truly not working as well as it's supposed to.

 

You don't want to clean it with solvents. They make cleaners you can buy and dump in your tank that's supposed to help, but I don't know how well they'll work.

 

If you can find seafoam, give that a shot www.seafoamsales.com

[cannonball]

I'll be curious to hear your report. I've had the same intermittant problem as well. Mine seems to come and go about every tank of gas. I replaced my O2 sensors around 80,000 and the light came back on about 120,000. This time I let it go until I can get to it. It doesn't seem to affect performance. I've put about 7,000 on it since.

[jlawlor]

I'll be curious to hear your report. I've had the same intermittant problem as well. Mine seems to come and go about every tank of gas. I replaced my O2 sensors around 80,000 and the light came back on about 120,000. This time I let it go until I can get to it. It doesn't seem to affect performance. I've put about 7,000 on it since.

 

I am replacing the cat. The Seafoam had no effect.

[cookie]

I have a 99 Forester and I do have the sensors sitting in the garage. I was thinking of replacing one of the two cats but I am not sure which one. I suppose eventually I'll have to do something about it. It's hard to get very motivated about it when it takes five minutes to clear and stays clear for six months.

[jlawlor]

I have a 99 Forester and I do have the sensors sitting in the garage. I was thinking of replacing one of the two cats but I am not sure which one. I suppose eventually I'll have to do something about it. It's hard to get very motivated about it when it takes five minutes to clear and stays clear for six months.

 

My light is on like clockwork at 200-300 miles. I've tried; cleaning the sensor contacts, blowing out the sensors, replacing the rear sensor, and 2 cans of Seafoam. Tomorrow I'll replace the cat - all for an annoying light.