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Don't know what car you have so that's one possible issue. Fill in your user profile with your car and location details, so that infor will appear in all your posts at the left. (Click on the avatar at upper right for Account Details, then on Account Settings.)

Website doesn't indicate it uses the FT232. There's a question about the chip from 2015 that says it's a CH340, but that could have changed since then. The CH340 unit might work, but as noted earlier, the FT232 seems to be more reliable.
 

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Don't know what car you have so that's one possible issue. Fill in your user profile with your car and location details, so that infor will appear in all your posts at the left. (Click on the avatar at upper right for Account Details, then on Account Settings.)

Website doesn't indicate it uses the FT232. There's a question about the chip from 2015 that says it's a CH340, but that could have changed since then. The CH340 unit might work, but as noted earlier, the FT232 seems to be more reliable.
Thanks. its a 2005 outback llbean 3.0 with 165,000 miles on the clock.

Dave
 

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2005 Subaru Outback 2.5i A/T
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Thank you for the confirmation!

Okay, so today turned into being a lot more involved than it needed to be. If you look 2 posts up you will see that my game plan for today was to swap sensors B1S2 and B2S2 since they are the same part number to see if I get erratic voltage readings from my other cat. I pulled B1S2 without issue but (I'm assuming) the idiots at the dealership cross-threaded B2S2 when they replaced the engine at 115k. I wasn't too worried about the sensor itself since it was the one giving me crazy voltage readings yesterday, I was more concerned about the bung. I tried to hand screw my other known good sensor (B1S2) into the bung and it wouldn't go. Lisle makes a tool (part number 12230) that you should order today for your box. I couldn't believe I didn't have one, but for $6, its made in the USA and a LIFESAVER.

I chased the threads and we were back in business. I was able to hand thread in my known good sensor into B2S2, but since I did not have a good sensor (Amazon has not arrived yet......), I put a drain plug into the other bung to cap it off and prevent it from sounding like an old Deere. I am SO happy to report that I am now getting a consistent .750v from B2S2 with my known good sensor that was in B1S2 yesterday. I'm really hoping that once the new sensor arrives and I put it in B1S2, we are fixed up and the P0420 is a thing of the past.

For the money, I'd prefer to replace both of these post primary cat sensors, however due to being unemployed, it's mission critical purchases only.
Well, P0420 is back, sigh. B2S2 voltages are jumping all over the map again... @plain OM , think this means the converter is toast?
 

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Well, P0420 is back, sigh. B2S2 voltages are jumping all over the map again... @plain OM , think this means the converter is toast?
Is the B1S2 sensor also in place now, and is it steady when the B2S2 is jumping all over the map? And how do the S2 voltages compare (movement activity) with the signals from two S1 pre-cat sensors?

In my view, the swap confirms that the original sensor probably wasn't faulty. But, we don't know what the conditions are when the voltages are jumping all over the map. It's normal for the post-cat sensor voltage to move in concert with changes in the throttle. As is mentioned often in this thread, data logs could be of more help. @cardoc is more familiar and experienced with assessing symptoms when there's a P0420.
 
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