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Cat convertor error code


tall_tog
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Starting to get disheartened with my outback 2005 2.5

new front 02 sensor fitted (genuine part)

check engine codes cleared 

bang on 100 miles check engine light back on

emissions beyond threshold 

cleared code , bottle of cat clean and bang on 100 miles check engine is back on.

rinse and repeat !

im doing lot of motorway miles just now and really misssing cruise control

having done some reading it seems there was a cat fault at some stage that Subaru did a recall for .

it also seems that it may not actually be the cat

had anyone else had this and how did you cure it please ?

notifications aren't working on here for me so I'm not being rude if I don't reply straight away! 

THanks in anticipation of enlightenment 

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Yes front sensor just been changed and some of the reading I've done would suggest it's not  as straight forward as being a cat fault 

seems odd or maybe coincidence that the check engine comes on at 100 miles after being reset

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I kept getting p0420, changed fuel company and haven't had it in awhile. Read online that the added ethanol some companies use can have an effect, but after clearing it you'll notice it takes 2 trips to come on and after the same time/miles.

Read up again that the rear o2 detects the cat isn't working like it should, the car then does 'checks' by pumping in more fuel for a second to see changes.

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Tried a tank of ultimate and mpg fell off a cliff ! 

Thing is having to keep paying to have code cleared is a right pain 

I'd rather pay for a sensor have code cleared and see what happens then

any other thoughts or experiences out there ?

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Did you try the tankful after clearing the code? That could possibly make your ecu relearn its values. The light should go away on its own after two or so drives when it passes it's little test and think the cat is working better

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No the ultimate tankful was a while ago 

so the code /check engine light will go off its self if things improve ? Thought they had to be cleared ?

think I'll try rear sensor given the front is new , chances are rear is on its way out too ?

if that doesn't sort it then I guess it means the cat is dead ?

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If it's the p0420 code, it will go away on its own after a certain amount of drives when everything's alright. (has to be from cold start to warm up, min miles etc) other codes you may need to clear, some people do this on their own by disconnecting Battery but your mpg can go up as you delete learnt values in the computer.

If it's the rear o2, that can have a separate code, saying the voltage appears too low or too high etc

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The garage that read your code might have been able to read what the rear o2 is reading, i think if the cat is dead it should read as if it was on the front (rich/lean/rich/lean etc) if the cat is working it should read a steady rich condition as the oxygen is used up to make a cleaner burn.

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Rather than pay a garage you could buy obd to usb cable and use freessm software on notebook or for a basic solution buy a simple code reader (10.99)
http://www.ebay.co.uk/itm/Car-Engine-Fault-Code-Reader-Diagnostic-Scanner-Reset-Tool-OBD-2-CAN-BUS-EOBD-UK-/172200936611
Some members on here used these fine and simple easy use solution if not into notebooks or no android phone to use a Bluetooth obd dongle and android torque app .

get the exact code & also check & clean sensor harness plugs with elec contact cleaner .I would guess it going be P0420 (Catalyst System Efficiency Below Threshold) which really is either the rear sensor as this is the one that relates data to cat efficiency.
sensor data can be read & sensor bench tests can be done, Cat itself could be an issue, also leaks in exhaust can cause it too .

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That code rarely linked to front sensor so mechanic probably not too clued up to replace that first.

cat could be fine at 130k but other issues such as oil & excessive fueling can shorten the lifespan .
rear sensor or related wiring is the more common one, rear sensor around £130 roughly and easy fit .

If you can fit a rear sensor yourself it probably better option than paying garage do tests .
Do check exhaust condition for potential leaks though .

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You could try some cat cleaner additive first, even try the additive twice and drive it hard so cat gets real hot.
This may bring some life back into a carbon blocked cat and clean sensor heads a bit.
2.5 head gasket issues can help reduce cat lifespan . lambda sensor has it's own fault code for main failures but it could be reading off and cured couple with rear sensor when no real fault data found to conclude anything else .
Hard one diagnose and expensive how ever you go about it.

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Previous owner to my 2001 2.5 legacy had that code, I got the car at 90,000 miles with that code coming on/off then it didn't come on for awhile. Went to a petrol station I hadn't used in awhile and it came on. Now at 180,000 miles and hasn't come on. Some companies blend their fuel to make it more environmentally friendly or cheaper etc, so just avoid them and should be ok. Now currently at 180,000 miles

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Don't think fuel is issue as not brand loyal

first bottle of cat clean was with low fuel level and gave it a good thrashing , second soon after was with full tank.

ill wait on gadget to clear code and change rear sensor , expensive but still cheaper than cat.

front sensor was £137

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Can't say I noticed a trend on fuel to P0420 .

You may find rear one for about £90 (from online lambda specialist such as ecolambda.co.uk) at best if cross match subaru part number, most cheaper ones still turn out be same denso sensor.Front one easier find cheap than rear rom last time I sourced one .
You could throw £100 at garage to check rear sensor and cat and still have a 50/50 diagnosis result . check connectors for sensors well & give them squirt of elec contact cleaner .

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Where abouts are you? I'm in Norwich, I have a scan tool that allows me to read sensors and reset codes etc. Perhaps you are near someone else on here with the same gadgets that can help you out and show you how to use them, then if you got your own you'd be comfortable with using them and keep it in your car.

Always good knowing what the codes are if one pops up and you're 100 miles from home!

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