I have a 2005 Sport model with the V6. I am getting a PO420 code as well as the check engine light and VSC lights. I replaced the downstream O2 sensor and lights went out for about 240 miles then came back on. New gas cap and zero point calibration done. So, I guess my next step is to replace the upstream passenger side O2 sensor.

I can't get the upstream O2 sensor unplugged. Has anybody got any tips? I haven't tried to loosen O2 sensor yet. That one looks to be a pain as well. Any tips on that?

If that doesn't fix it, I guess I can put on a new passenger side manifold and catalytic converter.

Running out of options and I really don't want to take it to the dealer.

Any help would be great!

Thanks!

Check the exhaust gaskets for leaks and look for holes before the down pipe.
It’s not likely to be the upstream sensor triggering that code.

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Check Engine Light Code P0420

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Thanks for the help! I'll look for exhaust leaks at the gasket. I know there are no holes in the exhaust pipe itself.

My mileage is about 20.8 mpg and it runs great. Just throwing that code.

I replaced the plugs and coils to rule them out.

My biggest thing right now is I just can't seem to get the upstream O2 sensor unplugged from the harness. Limited space but I can get my hand all over it. Can't feel a tab or anything to release the plug.

I'll keep trying. Any tips would be great.

Thanks again!

I know other people have said the upstream sensor isn't the issue, but if you're set on taking the sensor out here's what I remember. The upstream sensor is the same plug type as the lower sensor. I used a small flat blade screwdriver to press down on the tab. You could also try getting a pair of long-reach needle nose pliers in there to pull on the plug.

As a last resort, would pulling off the big plastic intake on top of the engine give you more room to work? Maybe the sensor is low enough that it doesn't matter, but itt's pretty easy. Just unclip the air filter section, then unscrew the two bolts holding it on. You'll also need to loosen the clamp at the very top/front of the engine where the MAF is and pull off the thin vacuum hose behind the big plastic intake. Keep in mind if you've never taken this piece off, you may need a new gasket for the bottom of this piece if you're current gasket is dry or cracked.

Are you thinking about swapping the upstream sensors so the passenger side is on the driver side and the driver side is on the passenger side? That would definitely help rule out the sensor. The driver side is a little harder to get out, but they can both be done with the right tools and a lot of patience.