[coves]

2012 Tribeca, 169000 miles. No other issues.
Well, I've tried all the hacks, and a few cleaners including lacquer thinner, and the CEL just keeps coming back like the crab grass in my yard. Maddening. Even the big buck computer analyzer continues to indicate improper voltages on the down stream sensors. Temp ck shows less than 50 degree F between front and rear of both cats. Even installed the hack of spark plug extenders on the down stream sensors. Get this! When those were installed the CEL still came on at the same frequency but when I would stop for gas and open the tank the CEL would shut off! WTF! But on highway driving the CEL would eventually pop back on. Never on short around town drives. Anyway, who has successfully and reasonably priced, replaced their cats? The OEM's are outrageously priced and being welded into the entire exhaust system you can't just unbolt and replace. What was Subaru thinking? Did I mention, maddening!!!

 

[Flat6er]

1) Tribecas do NOT have separate temperature sensors before/after catalytic convertors......
2) how about investigate further - is everything ok with gas tank ventilation? like reading carefully errors etc etc? may be replace gas tank cap and check if there are leaks in those hoses from tank to intake in EVAP system?
3) about catalytic converters - I tried to get like from law perspective - what are requirements, spoke with some exhaust shops - no clear answer. I guess they just check ecu monitors (pass/not pass) + visually it looks like catalytic converter and that is fine...
so... anyway - I was looking into catalytic converter thing from tuning perspective - but there are some options (these are more like ideas, not a researched solution!):
like walker 55639 ( ~600usd) and 56263 (~1400usd). (replaces original).
there are things like these - Products - G-Sport Catalytic Converter Parts & Accessories - but it also costs like 650usd/piece.
magnaflow have like ~1500 per each side exhaust fronts (with catalytic converter included).

or just go to local exhaust shop and talk to them - they will probably offer something more price effective (please, share what you find)

 

[coves]

All good ideas.
This is a 2012 Tribeca and unless I was totally hallucinating when I changed them out there is definitely an upstream and downstream sensor on each cat.
I've looked at some of the options you have mentioned. Problem is, two sensors on each cat that have to communicate properly with the computer or guess what...CEL. No cruise control. No ABS. This is just insane how Subaru has configured this system. And again, I can't be the only one that has run into this issue.

 

[coves]

Maybe time to post this issue and see what others have experienced.

 

[Flat6er]

upstream and downstream sensors are lambda/oxygen/whatever you call them sensors. and temperatures which you got from those - are heating elements for those sensors. any more fantasies to abolish?

you can turn off CELs in ECU and "live happily ever after". which might be good short term solution... in long term - your catalysts can get clogged and... you might have another set of "funny behaviour" ))

 

[coves]

Reporting in. CEL went on again on this last long distance drive. Waited 'till half tank of fuel, added one gallon of acetone. Reset CEL with battery disconnect. Just now back home after 150 mile trip. No CEL. Jury still out. Holding breath.
BTW, you mentioned turning off CEL via the ECU. This is different than just a reset by disconnecting the battery? Please elaborate and how this is done.
And to continue to beat this to death, it is my understanding the "sensors" are designed to react to the upstream and downstream exhaust temps and in turn register specific voltage values that the ECU recognizes as normal vs abnormal.
Not only were the temp differentials via upstream and downstream via my IR thermometer out of range, but the fancy OBD tool indicated wrong voltages at both downstream sensors but normal with the upstream. This all seems to indicate malfunctioning cats.
Thanks for hanging in here with this discussion. However weird this sounds, I find these kinds of things fascinating.

 

[Flat6er]

1) just remember to refill your gas tank full of pure gas. Pumps, filters, hoses might not be happy with acetone
2) ecu has ability to “forget” that particular DTC/CEL exists. If you have “definition” for yours - check radiobutton to off, save, flash ecu and “live happily ever after”(until you clog catalysts and you won’t be able to drive 🤣
3) lambda sensors detect oxygen in exhaust gases. For their proper functioning - they need to be warmed up(that’s why - say- older cars might drive fine for like 10-15minutes and then start jerking you around). Also - with time they degrade and become “slow”… also bad. To understand what is going on with your situation - note short term and long term fuel trims first.
Then also would be helpful to do some logging…
And since you haven’t provided anything real - no temperature, no value for lambdas… hard to tell what are you talking about 🤣

 

[Jefferson]

There are about a thousand and one reasons that the p0420 code pops up. There is a real good thread about this on the outback forum. Anything from vacuum or exhaust leaks, bad fuel, dirty or bad injectors, engine temp too cool, bad grounds, pcv valve and so on. It would behoove you to look into other causes before replacing the cats as the code will come right back if you haven't fixed the root cause.

 

[Flat6er]

There are about a thousand and one reasons that the p0420 code pops up.

I didn’t see him mentioning exact error code… did I skip it unintentionaly?

 

[Jefferson]

He didn't mention it, but that's the code for catalytic converter insufficiency and it is I believe the most common code that crops up.

 

[Flat6er]

checked again - I wasn't aware there is just one code for that inefficiency (despite it's name mentioning bank 1