My HX has 325K on the clock and I recently installed a new converter (not OEM & cheap) to hopefully remedy a PO420 code. I have been getting by (for years) with after market O-2 sensors both up-stream and down stream and still able to attain over 40 mpg on the freeway doing 65-70 while holding Lean Burn. As of late the fuel mileage around town has taken a significant drop which has initiated my reading codes. The PO420 continued to come back after repeated re-sets. The down stream sensor fluctuates up and down; at WOT it will hit .9volts and on the coast .2 volts. The up-steam has been real lazy hanging in the .505 voltage range with very little fluctuation at WOT and coast.
In the several years I have owned this car I have never bought the high dollar NTK 24300 up-stream O-2 sensor, nor a high quality CAT. Indeed I have tried to cheat the system and it appears that gig is over. Before I blindly lay down the $236 that Amazon wants for the sensor (OEM Honda $600). I wanted to gain more knowledge on how the Up-stream and down stream sensors react at WOT & Cruise & coast. What is the upstream O-2 doing to make it so expensive? I am using a hand held scan tool* that can record freeze frame and read all the data from the various sensors.
Additionally, I recall that CAT converters use a few grams of platinum in the substrate. At the price (E-bay) I paid for the CAT, there cannot be any Platinum in it. This is the third CAT that has been in the car since I bought it with 185K miles. All the while chasing down the PO420 code.
I am grateful you have read this far, if you could pass on some good education about this HX and the O-2 sensors I would be very appreciative. Try not to lambast me for not buying OEM Honda parts! This car has hail damage, cracked windshield, and some dents, so spending real tall dollars on a $900 car does not make sense. Need I mention, my wife would like to see it go away, but that 40+ mpg on the freeway is hard to walk away from.
*Autel AL-519

 

I was hoping I would get someone to enlighten me on the 5 wire high dollar O-2 sensor - the upstream that is mounted directly in the CAT/exhaust manifold.
Rock Auto has one listed for the HX- Manual trans for $220.79 Any other part numbers would be appreciated.

 

That's the sensor that you need to buy.

 

I would recommend buying direct from NTK for the O2 sensor rather than amazon if you still can. Amazon is full of counterfeit auto parts, particularly when it comes to high dollar small components.

I have had good luck with magnaflow CAT converters.

Tall money on a $900 car is money well spent when new cars cost $40,000+

 

Good tip.