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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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Below is the graph for the rear sensor. The battery voltage is good, the AF correction is okay for what the ECM is trying do and the engine temperature is good. When you see the rear O2 data fluctuating in this type of way, it means the catalytic converter is dead. The ECM controls the HC output of the engine and the effectiveness of the catalytic converter through fuel management. By alternating rich to lean to rich and continuing this pattern, it allows the engine to function at a good level of performance and the catalytic converter functioning by not overloading it with fuel that cools it off inhibiting function. Stoichiometric equation to achieve 14.7:1 is only to keep hydrocarbons low. Gasoline engines run better and more powerful at richer mixes, closer to 11:1. But the rich combustion dictates higher CO and HC, so it was determined that leaning the fuel ratio would keep emissions on a lower scale, but it was necessary to fluctuate the enrichment to balance everything out. The fluctuation is typically seen in front sensor values on the low voltage scale. Rich is higher voltage values close to 1.0V, lean is low values to 0.0V. Seeing this type of pattern indicates the cat is not reburning and converting the exhaust. Its either incapable of heating up or the substrate is coated with carbon and/or varnishes from the exhaust running rich over time. What you should see is a steady line in the 0.6V-0.8V range. There may be a little fluctuation in the line up and down, but not the severe changes indicated in your data.

Been diging in here for the last hour or so..... best explanation with a waveform pic yet! Thanks!
 

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2001 Outback H6 3.0l VDC
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Heyo, time to join the fray. I've had the 420 on and off for the last month and a half or so. I thought it fixed itself when I changed over from Wawa gas to primarily Shell + a couple of cans of Seafoam over a couple of consecutive tanks, but it came back. It came and went a lot in the beginning before disappearing for an entire week plus a 400 mile drive only to reappear on the way way back. It's been on the longest now at a couple of weeks. I had thought it might be my upper radiator hose leaking coolant right onto the rear o2 sensor because of the cold weather, old hoses, and also the worm gear hose clamp securing it, but I replaced all the hoses and got fresh spring clamps and it's still here. I haven't noticed an vacuum leaks though I might have an exhaust leak, judging by the exhaust smell on a cold start. I found this thread when I first got the code and I've been monitoring things with romraider. The graph for my o2 sensor stays relatively flat (most of the time) at idle but at speed it is a waveform. I can get it to stabilize somewhat holding an exact speed on a flat road but I'm not sure if it's supposed to be that precise of a test? Anyway I have a couple of logs to share - an idle, 0-70, and for some reason two cruising at ~70. Actually one might be going uphill taken for my own curiosity because I noticed that my knock correction had at some point hit 31.98 degrees which seems like a lot. Typically the max I see is 7 or 8.something. Enough rambling though. This car is an 07 legacy wagon 2.5i with 83k. I don't think I've updated my profile with it yet. Thank you so much for any guidance y'all can offer.
https://www.dropbox.com/s/k2bi3reyt03sfi6/07 legacy logs.zip?dl=0


Sent from my iPhone using Tapatalk
 

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noobie OB owner seeks to use intelligence to correctly diagnose P0420 code, thinks himself geeky enough to rig up OBDII on board thingy mcbobs, wonders if this cable will work:
run to PC laptop running some newer flavor of Windows, can't remember which as he is a Mac guy, and RomRaider then spend countless hours trying to get it to work and then more time interpret the data, time well spent;

decent cable choice? says FT232
 

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2014 Outback 2.5 Li CVT + 1985 GL 4WD Wagon
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133k miles. Owned it for 5k. First check engine light of ownership gave me a P0420. No symptoms present. Car runs great and gets ~26 mpg mixed use in the mountains.

I had both gotten gas at a different place, a Sinclair, and changed the oil less than 100 miles ago. Hit a rough patch of road before it came up also.

Checked and tightened my oil fill cap and gas cap, reset the code. Oil cap was tight. Filled 1/2 tank with known quality gas.

No reoccurrence in about 200 miles now. Hoping it was one of those caps, but if it comes back I'll start the real diagnosis.
 

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2.5L 2008 Outback Touring Wagon
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So I've been trying to pin this down when I've had time (rarely), and I was wondering about a potential cause that I haven't seen mentioned yet. I searched this thread for P0420 +"air filter" and nothing came up.

As I mentioned in my welcome thread ("New user, old subie owner, with 08 Aussie spec") I only get a P0420 and MIL when driving at highway speeds (100kmh/60mph). I can drive around here for weeks and weeks - top speed 80kmh/50mph - and everything is fine.

Within 10-15 minutes of hitting the highway, up comes the MIL and it's always a P0420. Now the car is coming up for a major service (250,000km), so the air filter is at the end of its life and will be replaced.

Is it possible that the air filter is clogged to the point of being able to pass sufficient air up to ~100kmh, but not beyond that? Obviously there are times where the RPM (and demand for air) at suburban speeds matches or exceeds that of RPM at highway speeds, but it's not sustained. Is it possible that there's just not enough intake airflow to maintain a healthy emissions system at sustained highway RPM ? Just a thought.
 

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noobie OB owner seeks to use intelligence to correctly diagnose P0420 code, thinks himself geeky enough to rig up OBDII on board thingy mcbobs, wonders if this cable will work:
run to PC laptop running some newer flavor of Windows, can't remember which as he is a Mac guy, and RomRaider then spend countless hours trying to get it to work and then more time interpret the data, time well spent;

decent cable choice? says FT232
That cable seems totally bogus, nothing recognizes it, I can't get any drivers going, the supplied CD is full of garbage, I took it apart to check the chipset, they are NOT labeled FTDI anywhere, not labeled at all
 

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I only get a P0420 and MIL when driving at highway speeds (100kmh/60mph). I can drive around here for weeks and weeks - top speed 80kmh/50mph - and everything is fine.
That could be due to the particular criteria for determining if there's a P0420 fault. (I'm sure I posted the North American FSM criteria pages here, but it's some time back.)

As I understand it, the OBD checks for the fault once in each drive cycle, and only when a list of pre-conditions is met, including the car moving at 70 kph. The detecting criteria have to be met in two consecutive drive cycles in order for the the code be set and the MIL turned on. Consequently, it's possible that on one trip the fault is detected, but on the next trip the pre-conditions are not met or the fault is not detected. That resets the two-drive-cycle counter so on a third trip, if the fault is detected, it still doesn't turn on the CEL.

As for the air filter being a factor, I tend to think it unlikely, but it's fairly easy to check/replace, and if it hasn't been done for some time, or the driving conditions have been such that it would tend to become clogged earlier than normal, probably a good idea to change it regardless.
 

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That cable seems totally bogus, nothing recognizes it, I can't get any drivers going, the supplied CD is full of garbage, I took it apart to check the chipset, they are NOT labeled FTDI anywhere, not labeled at all
Thanks for that update.

The reviews on the Amazon page aren't very supportive. There's always some that don't work for everyone, but this one seems to be weighted to the negative end of the spectrum. Are you still within the return window?

The last Vag-Com KKL 401.9 cable I bought a few months ago was from an eBay supplier in the NY or NJ area. Standard blue colored-version. Look back in this thread; there's probably some posts in the past 6-12 months where someone posted the link to a cable that they had picked up and it works.
 

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Thanks for that update.

The reviews on the Amazon page aren't very supportive. There's always some that don't work for everyone, but this one seems to be weighted to the negative end of the spectrum. Are you still within the return window?

The last Vag-Com KKL 401.9 cable I bought a few months ago was from an eBay supplier in the NY or NJ area. Standard blue colored-version. Look back in this thread; there's probably some posts in the past 6-12 months where someone posted the link to a cable that they had picked up and it works.
Yes, it was purchased Amazon Prime so it's going back. Ironically I saw advise to avoid the KKL cable somewhere. I may try again I may not. It's still possible it wasn't the cable but was me, I spent a good 4 hours trying to get it work on two different laptops with two versions of Windows. I threw in the towel on this one. The weird thing is my Mac reported it as an FTDI FT232 cable at one point but the Windows machines wouldn't recognize it as anything. Now my my Mac doesn't either, when plugged into the car's port it does light up.
 

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Rear O2 readings seem erratic to me, bad cat? the rear sensor was replaced by selling used car dealer, it's a Denso, maybe it is the cat, or winter gas, maybe it's spark anti fouler spacer time? hmm, here's log if someone is interested
supposed to be a drop box link, no idea what I'm doing
Yes, it continues to oscillate (i.e., erratic) during relatively steady-state driving.

There isn't much rear O2 data during warmed-up idling; erratic signalling at that time is often also an indicator of a bad cat, or, a bad rear O2 sensor!

A/F Correction is showing jitter that might be due to the erratic rear O2 sensor signal. (Both the A/F Sensor and Rear O2 Sensor are inputs to the fuel trim function.)

@cardoc ?
 

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2001 VDC/SC One of a Kind
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@AkuPen

The cat is bad. You need to figure out what is causing the knock, though. It could be carbon build up in the combustion or it's time for a timing belt. I know the mileage is low, but I've seen some EJ253s that had a loose belt as early as 80k miles.
 

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@jvandyke

I need to see TPS % and knock correction to determine why the fuel trim is all over the place. Also Ignition timing.

I think the cat is toast, but need to see what killed it. If you replace the cat, the new one will suffer.

And the pre-start battery voltage is low. How old is the battery and have you checked conductance through the battery cables?
 
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