P0420 question

[Bostonian1976]

Everyone's favorite code! Mine doesn't come on for a good 300 miles after reset but it does eventually come on

 

So far I've done air filter (very dirty), plugs (.060 worn instead of .044)

 

Next I'll do o2 sensors before surrendering to cat

 

Here's my question. The dealer tested my o2 sensors and said they're cycling. Could they possibly still be bad or does that 100% exclude them? Thanks!!

 

This is a 2000 Outback

Edited December 19, 2010 by Bostonian1976

[idosubaru]

First - make sure there are absolutely no exhaust leaks.

 

Next step is to replace the rear O2 sensor.

Replacing the front sensor won't likely fix the code but personally I figure I'm going to put a lot more miles on the car anyway so why not replace the front.

 

Final step is to install a $5 spacer on the rear sensor.

 

Replacing the catalytic converter is pointless.

[johnceggleston]

 

Next step is to replace the rear????? O2 sensor.

Replacing the front sensor won't likely fix the code but personally I figure I'm going to put a lot more miles on the car anyway so why not replace the front.

 

Final step is to install a $5 spacer on the rear sensor.

 

 

huh? i'm confused.

[idosubaru]

huh? i'm confused.

right on JCE, or skip that step i meant to add.

i figure a lot of folks....particularly someone wanting to replace a catalytic converter is going reject installing the rear spacer first.

[GeneralDisorder]

As long as mileage and performance aren't suffering - I just go right to the spacer. Less time and frustration involved that way. Once you do that all you have to typically worry about is the front sensor for mixture control.

 

GD

[Bostonian1976]

Well - I have to pass emissions and when the code comes on mileage drops considerably. What spacer? The drilled out anti-foul thing I read about?

[idosubaru]

What spacer? The drilled out anti-foul thing I read about?

correct. you can buy them ready to install off ebay for $5, no drilling, etc.

 

if your mileage is bad, rear O2 doesn't affect mileage, only the front does. but so do plugs, wires, filters, etc.

[Bostonian1976]

Thanks! Mileage only becomes bad when CEL comes on (then I reset it)