The downstream O2 sensor sets the P0420 code, the upstream sensor has no part in it.
The upstream O2 sensor is responsible for controlling the A/F ratio.
If you are clearing codes all of the OBD2 tests have to start like from factory. In my experience the P0420 test runs just after the last EVAP test runs, which can be 10 days later.
Are you checking the coolant level under the pressure cap?

 

What does your Windshield washer fluid look like?

 

The "green" coloring is copper corrosion of the wires, somewhere water or other liquid is getting into the wires and water always run downstream and pools in those connectors. even if you clean them it will continue, but if you clean them and apply dialectic grease it should retard it for awhile yet the inside of the wires will still continue to corrode with green goo. has the car been in a flood or driven through deep puddles ?

 

How did you clean the O2 sen sor?

 

That IS a mystery….you might have to call Ghostbusters…lol

 

Hello all and thanks again for your replies.
To answer all the posts;

Whenever the upstream sensor connector fills with goo the codes that come up are MAF, Up and Downstream. Cleaning or replacing the upstream O2 ends those codes until it fills up with the goo again. This has been the case for 5 years.

The windshield washer fluid is blue. I deliberately stay away from any fluid that is green to try to figure this mystery out.

I have peeled back the wires on on the O2 sensor and never found anything liquid. I have also dabbed the ends of the connector lead with silicone and dabbed it on the wires to form a "break" for any capillary action. (Through the years I have taken all the advice of every mechanic that saw this goo.) I have not put dielectric grease on yet. I figure that is just a preventative measure and I want to learn what actually causes the accumulation of the goo. Also; I am afraid that when I'm out traveling I won't be able to clean the connection with grease on it if I have to. (I keep a spare and have changed it on the side of the highway burning myself several times.) This time I WILL try try dielectric grease.

I clean it by first spilling out the goo, tapping the connection to force as much out and then blotting as much away with a paper towel and q-tips. Sometimes I spray it out with brake or carb cleaner and spray that out with air and let it dry.I use half paper towels and by the time I'm done 80% of the paper towel is green.

The last reply:
I tried calling Ghostbusters, but ever since they merged with Ghosts R Us it has become too complicated to reach them. I go through hours of prompts on their phone only to be put on hold for hours listening to the Macarena.

 

Spray with electric contact cleaner, not brake cleaner or carb cleaner, both will invite corrosion to the connector.

 

NEVER let silicone get near an O2 sensor. That will destroy the sensor.

 

Sorry about the useless “Ghostbusters” comment…lol. I am very interested to find out what is causing it myself. Sure looks like anti-freeze….(I know you said you had orange Dex-cool in it). As far as copper corrosion, most of my experiences it has a blue tint to it….and I dont see any blueish green,…just green.
How about carwash fluid? Any chance that is where it comes from?

 

I'm still trying to figure out what name I could possibly call or argue about.
The simple answer is "I don't know". The pics look like green anti freeze not goo. The only way I can figure is that someone is spraying something green on it, maybe some sort of engine cleaner? There is no liquid that color that lives under the hood of a stock HHR.
Again, do not use silicone anywhere that it could get into the exhaust flow or the O2 sensors. It is deadly to sensors and catalyst.

O2 sensors have a through hole in them because the way they work is to compare the ambient air to the exhaust gas. Any silicone on the outside can get inside.