brus brother

Thanks GD. I don't have live data ability. Small correction in original post. the front a/f sensor was replaced at 105K miles. Cured nothing. Mis-diagnosis by wallet! Today the passenger cat was replaced (Eastern Catalytic converter) and still throwing p0420. Their "direct fit" required additional gasket to fit! I have a new o2 sensor for that cat which I will swap in as soon as the car cools down. Subaru tech suggested that I might have to change out driver's side cat as well. Apparently that is sop in the shop as they want the $ and don't want the customer returning dissatisfied with same CEL complaint. He also suggested that our winter gas here in CT that kills cats.

My 05 auto outback has two precat air fuel sensors, two post cat oxygen sensors and one oxygen sensor on the rear cat. P0420 giving me a headache. No obvious exhaust leak. Got a cheap cat and will be installing tomorrow. Changed the post cat sensor at 105 k miles when code first appeared but that changed nothing. Now at 190 k miles fingers crossed. Could the rear cat and or sensor relate to the p0420?

Any recommendations for O2 sensors for 05 Outback AT? 195K miles. Pesky P0420 has worn me down. Started at 105K miles. After 6 years of being able to clear code and set readiness parameters for Emissions inspections here in CT, the code now comes back almost immediately after clearing. Many years ago CarDoc on the Outback forum had diagnosed the cat as bad after having me run some live scans (I can't remember which at this point). Before that, at 105K miles, I had changed the front O2 sensor (behind the first cat) but that didn't help. I did not change the front air fuel ratio sensor (before the first cat) at that time. Ordered a $200 Cat from Eastern Catalytic but fear that the sensors may also be shot. Haven't detected any exhaust leaks. Car runs fine. Gas mileage hasn't changed. Inspection is due in 2 weeks so I am trying to get my ducks in a row.

brave cameraman!

is there vibration in the steering wheel or do you just feel it in the seat

A good start but while possibly hitting the nail on the head, the diagnosis might not be definitive IF one of the rear tires is also out of balance/bent rim.

get your tires balanced. cheap and easy on the back. Start simple but if that doesn't solve your issue then dig deeper into the soup pot. common things happen most commonly...

tire balance

to be clear, you ran it with ONLY the new first and original second cat pipes connected (everything beyond the second cat pipe was disconnected) and had the loss of power symptoms? well that seems to have now isolated a constriction in that second cat curious why you earlier sensed there was restricted output at the right tail pipe. where are you getting your parts from? can you link a schematic of your original exhaust system? cats are expensive little items.

While you wait for your bore scope to arrive, disconnect then reconnect exhaust components sequentially until the symptoms disappear. Seems pretty simple although tedious. You would have to do this to use your bore scope anyways. If you trust your suspicion, then start in the rear with that R muffler although it could be a restriction just ahead of that component then move L and then forward. Each time evaluate to see if symptoms improve.

Not sure but there are brighter bulbs on the USMB than myself who might explain the metallic shavings external to the cat. Did you remove the cat or just disconnect it from the upstream flow? I would suggest you remove the cat entirely and have a look from each end to see what the damage looks like. also shake the converter to see if there are any rattling sounds indicative of loose honeycomb material. Assuming that spray cleaning the MAF was unrelated to the improvement, at this point, simply disconnecting the cat as you have only tells you that there is an obstruction somewhere beyond the area you disconnected. The honeycomb certainly appears to be failing but it would seem that for your situation, I would expect pieces of the material the size of grapes and larger to have caused a clog. I had started posting the above but then stopped, thinking you had solved the problem but it appears that you may have a restriction further down the line. Disconnect the exhaust and run again. If power restored then you still have a restriction

yup a real varoom machine! So after you reconnected the exhaust, was the power still restored or did it once again show signs of constriction? As I said previously, my buddy took his cat off and cleared out the broken bits and then reattached. No codes or anything. I read here in the past that people experiencing loss of power when going uphill resulted from gravity moving the bits of cat comb back into the air flow. seems like you are narrowing down the causes.

did you run with the cat disconnected? was the loss of power resolved or unchanged?

While you did say the noise was to the right of driver, in the front of the car, in my case similar symptoms turned out to be drive shaft u joint. You still haven't identified the year/model of the car. As GD pointed out, 05+ have bolt on hub/wheel bearing assembly which will save you money and time.

clogged cat? saw this on a friend's van. started out gradual loss of power then wouldn't even move! disconnected cat and ran that loud sucker home. removed cat and dumped out pieces of honeycomb. Reinstalled as far as I know, it is running to this day.

Nice write up. Is there reason to believe that the tubes could not be cleared without full dissection of the roof of the car? Fine wire threaded through the tubes assisted with compressed air?

a shop did it on my 08 came out pretty good

Not sure of the compatibility with the material you are looking to bond but I have had pretty remarkable success using crazy (super) glue methods below. Basically, lightly tag the pieces together and let dry. I prefer the liquid and not gel formulations. Then add a layer of fiberglass cloth and once in position, soak the cloth in more crazy glue. Build up a few layers if you have room. I used this technique on butt joints with great success. Also, if you aren't already aware, the addition of baking soda to crazy glue makes a rock hard "plastic". So, after initial tag tacking, if the space is limited, once you wet the surface of the area to be bonded, sprinkle baking soda on the area and wet the area with crazy glue so as to create a callous over the area to be bonded. There are many videos on youtube that show these techniques.

As mentioned above, autozone, advanced auto and similar chain auto retailers will read the engine codes for free. while you re there, ask them to check the alternator.

two issues: 1. is there a sunroof? clogged/disconnected drain tubes? 2. there are numerous posts about sealing the rear light assembly

custom? LINK here's a guy that adds a Crown Vic honeycomb to his subie ride.

not sure about your model/year but there may be some test connectors hanging beneath the steering column that would likely be unrelated to your issue.

Gas tank as you specified. I pulled into a commuter parking lot next to highway. Clear code. Drive onto highway and maintain 55 for 5-10 minutes. Exit highway and reenter back towards starting point maintaining speed. Exit highway, check system readiness and then scoot over to test station. That is the voodoo that has worked for me.

I have an 05 OB with all of the same sensors. The trick of taking the sensor out of the stream with the extender didn't work on my car. I first got the dreaded P0420 code at 105K miles so consider yourself lucky. I tried the extender and then even tried changing the passenger side front O2 sensor and still threw the code. My check engine light will go out occasionally but will eventually turn on again. I was told that I would need to change out the front cat on the passenger side. Apparently, these cars are running so lean that they can often read "above threshold" according to the ECU. My solution for the past 8 years in order to pass emissions was to buy an inexpensive $14 code reader similar to THIS I clear the code using the device. Next start the car and let it idle for 5 minutes without touching the gas then next do a 50 mph drive for about 10 minutes without braking or hard acceleration to "reset" the systems required to pass inspections. Turn off the car and using the code reader, rescan for codes and then for system readiness and then hightail it to the inspection station and am good for another 2 years.