Mystery wiring harness. 2003 gt.

[Vortec]

My gf has a 2003 vibe gt. While replacing her o2 sensors (hoping to get rid of the dreaded p0420) I found a white disconnected wiring harness where the dash center console below the shifter meets the carpet on the passenger side. wires were: 1 green, 1 yellow, 2 white. It closely resembled an o2 sensor male plug but I didn't find a corresponding female plug nor see exactly where the wiring ran. Anybody know what it is/does and where it needs to be plugged in?

Thanks


Side notes:

CEL returned and it's almost inspection time so I guess i'll be trying the diode mod or putting in a new cat soon (suggestions for one that actually works would be appreciated!). Not cool.

engine runs smoothly and strong. Spark plugs look good, no oil fouling or abnormal deposits/wear. mpg is upper 20s in mostly city driving. Haven't checked MAF.

[Flip-Side]

That code is almost exclusively o2 sensors or the cat. You will see a ridiculous number of posts on it because people are hesitant to drop several hundred dollars to replace the cat. Everyone wants a magic fix, and we try everything first, but what it usually comes down to is a blown out catalytic converter if you have already checked the o2 sensors. Best thing to do is to get down and rap on the side of it when it has cooled off. Mine sounded like a maraca, completely blown out.

[Vortec]

Yeah, I figured the cat is the real problem but I've already done the basic cat checks like bopping it to check for broken substrate and I used my pressure gauge in the O2 sensor bungs to check for a clog, so thankfully it just seems to be typical loss of catalyst efficiency from normal fuel deposits.

But my real question is what is this plug for? If it's part of the circuit it could be an issue.

Thanks

[joatmon]

Since the various types have the same wire harness, my guess is that the connector is used in automatic transmission Vibes, for either the shifter illumination and/or the shiftlock mechanism.

I can testify that if you leave an O2 sensor disconnected, you will quickly throw a CEL code other than P0420. Can't remember what thecode is, but I've done it, and it complains pretty quickly

When my cat converters have failed, they have not "blown out", but instead just stopped converting. I've read where the ethanol now in fuel dissolves engine oil additives from the cylinder walls, passing it to the exhaust, and some of these additives can contaminate, coat or otherwise kill the converters catalyst. For lack of any evidence, I'll blame it on that

[lannvouivre]

The way the converter works is by having contaminants stick to it until other molecules hit them so that they form less harmful substances. Just learned about it in Chem II...lol

[Vortec]

Chem 2 huh? I wish it was just that simple. Back in college we had to do full calculations for the prof's cat. 3-way magnaflow with air injection. Knda fun....well, for school as anyway.

Interesting thought about it being an unused plug for auto trans. Common harness sounds feasible for cost saving.

The old days, when we had pellet cats instead of brick, were great. Yes they were restrictive but that's easy to solve. Pop the plug, get all the pellets out and drive with good power and mpg for a year. Then put them back in for inspection.