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Guest Message by DevFuse

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2001 Outback Check Engine Light-Catalytic Converter??

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5 replies to this topic

#1 Mikle48


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Posted 20 July 2009 - 09:57 AM

I have a 2001 Subaru Outback with approximately 120,000 miles on it. I am not much of a mechanic so I apologize in advance if I appear somewhat befuddled. A little while ago my Outback's "Check Engine Light" came on so I took it to the Subaru Dealer to diagnose the problem. They said they found a, code for catalyst outside the efficiency threshold. I think the code is P0420. They cleared the code and put a can of BG 44k in the fuel and said this will sometimes help, and it did keep the check engine light off for most of the first tank, but then the check engine light came back on again. I put another can of BG 44K in the second tank, but it didn't help. The third tank I again put BG 44k in, but this time I used premium gas. Soon the light went out which made me happy, but when the tank got down 3/4, the light came back on again so I have aborted using the BG 44k (at $25 a can it is pretty costly).

In all fairness to the deal, they did say that the use of BG 44K was a long shot, but the alternative is a costly $1800 repair, which I assume is a new catalytic converter. So I am hoping to get some thoughts, ideas, comments on whether to proceed with the repairs or not. It makes me wonder what caused the problem in the first place and will it happen again to a new converter. I would like to keep this vehicle on the road and don't want to cause permanent damage, but the estimate makes me wonder if it is a good investment. Your ideas would be most welcome and helpful.

#2 Gloyale


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Posted 20 July 2009 - 10:17 AM

all that code means is that the Oxygen Sensor is outputting bad data.

The computer has no way of knowing if the bad data is because the Catalytic Converter is bad, or if the Sensor itself is faulty. Sensors go bad alot. Catalytics on the other hand, well they are chunks of metal with no moving parts......not really prone to failure ya know.

Replace the sensors first. 90% of the time, that clears this up.

Then if you do need a new cat(s), you have brand new sensors ready to go in them.

#3 avk


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Posted 20 July 2009 - 10:27 AM

I had this code about 2 years ago on my 1995 2.2 l Impreza and did two things: repaired a rusted out flexible joint, and replaced the front oxygen sensor. The code has not come back. I believe it was the front sensor which made the difference, as the leaking joint was past both the front and the rear sensors. P0420 is set based on comparing the readings from the two sensors. The rear sensor has to be switching between "rich" and "lean" at a sufficiently slower rate than the front. If the front sensor becomes slow, it might set the code as if the converter was bad. The code can also be caused by a leak in the exhaust system.
A 2001 model should have more refined OBDII diagnostics algorithms than 1995 (the 1st year), and the front sensor is a wideband type, but who knows. The sensor waveform can be tested, but if this is something you'd have to pay for (or to buy proper equipment for), you can just try and replace the sensor, after inspecting the pipework. At this mileage, it wouldn't be a waste. Besides, you'd still want to put a new one in if you were replacing the converter.

OK, I am slow to type.

Edited by avk, 20 July 2009 - 10:32 AM.

#4 jermany755


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Posted 20 July 2009 - 10:37 AM

What they said about the O2 sensors is true but even if your cat is shot $1800 is steep. A new OEM catpipe casts $1000-$1200 and is super easy to change out yourself. Do the sensors first though.

#5 Fairtax4me



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Posted 20 July 2009 - 10:55 PM

BG 44K is a super strength fuel system cleaner. It mainly cleans fuel injectors, intake ports/ valves, and combustion chamber carbon buildup. If one can doesn't fix the problem then stuff has to start being replaced. I've never heard of it helping a possibly bad catalytic converter.
To continue to use it is just a waste of money. At least your fuel system got a good cleaning out of the three cans you did use. :eek:

Catalytics on the other hand, well they are chunks of metal with no moving parts...

So is the O2 sensor... But instead of creating cleaner exhaust it creates a small amount of electricity.

I'd change both O2 sensors. Recommended change interval for those is usually 100k miles anyway.
What other maintenance have you had done recently? Has the fuel filter been changed? Spark plugs? Plug wires? Coolant flush? Anything like that?

#6 nipper


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Posted 20 July 2009 - 11:40 PM

useing too much of a cleaner additive can do mor eharm then good.

replace the front O2 sensor first with one from OE. You are at the right mileage to have a bad front O2 sensor.

The dealer is just lazy in not properly diagnosing the issue. Its like saying you need tires so replace the car. There is some logic to it, but its just cheaper to replace the tires.


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