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September 20, 2018, 07:37:15 AM
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Author Topic: 2011 Impreza - Just threw P0420 code  (Read 806 times)

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Offline Clutch

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2011 Impreza - Just threw P0420 code
« on: February 19, 2018, 08:39:47 AM »
Good Morning All.

Driving home last night, I got a CEL, flashing cruise and the no stability control light, which is always what you like to see...  Pulled the code and its P0420.  A little googling tells me this can be all sorts of stuff, other than potentially a bad cat.  A little backstory:

- Had car inspected a week or so ago, and took it to Hoffmans Jiffy Lube (dont hate, I was 3 months over on my sticker).  They of course pulled the filter to try and sell me a new one, and when I looked under the hood yesterday it looks like they just mashed it in there.  Wondering if there is an air leak near the MAF.
- Replaced my alternator and A/C belt yesterday.  First time doing a stretch fit belt, and its a huge PITA to bar the engine over under compression.  I doubt this has anything to do with anything, but figured I would mention it.
- Put gas in it in VT on Saturday, but its a different station than I usually use.
- Have had an exhaust rattle for a while, but figure its a heat shield since the band clamp is broken and I havent wanted to wiggle around on my muddy driveway to fix it.

So saying all that any ideas on where I should start first?  I have about 82k on it, and keep up on all of my maintenance.  Ill check the air box and those connections and will clean the MAF, but not sure where to look next.  Any known spots for a vacuum leak I should check? 

I have an ultragauge, so I can monitor the O2 sensor voltage, any idea what I should be seeing if those are working OK?

End of the day, I really dont want to put a new cat in this thing.  (even though its from PA, so its the non-California emissions, but I cant get a cat shipped here unless its the silly expensive one.)

Any thoughts?

Offline deadlydave

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Re: 2011 Impreza - Just threw P0420 code
« Reply #1 on: February 20, 2018, 09:56:38 AM »
- Had car inspected a week or so ago, and took it to Hoffmans Jiffy Lube (dont hate, I was 3 months over on my sticker).  They of course pulled the filter to try and sell me a new one, and when I looked under the hood yesterday it looks like they just mashed it in there.  Wondering if there is an air leak near the MAF.


I think this is the likely culprit, and easiest to fix.  Sorry that the monkeys messed up such a simple job.  :-(

Offline Clutch

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Re: 2011 Impreza - Just threw P0420 code
« Reply #2 on: February 20, 2018, 12:18:54 PM »
Thanks for the reassurance!  I cleaned the MAF, and tightened all of the connections yesterday, and cleared the code this morning before the drive in.  No return of the CEL, but its only been one drive cycle. 

Something did smell a little burn-y when I got out of my car at the office, so Ill have to dig into that a little bit more to make sure something bad isnt going on.  Fingers crossed that Im not signing myself up for a lot of wrenching in the next few weeks....

Offline FastfreddyRs

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Re: 2011 Impreza - Just threw P0420 code
« Reply #3 on: February 20, 2018, 10:47:09 PM »
Cat if bad is covered to over 150k miles. 
SubySolutions  -  518-222-9043  For all your Subaru needs.

Offline Clutch

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Re: 2011 Impreza - Just threw P0420 code
« Reply #4 on: February 26, 2018, 07:02:10 AM »
Thanks Fred.  I thought it was only 8 years, 80k for some reason, good to know I have some more time. 

For now it looks like all is well.  No code has come back, and when watching my downstream O2 sensor it stays pretty constant around .7 volts.  Long term fuel trim is a little negative, but everything seems to be running alright.  Put some Techron in my latest tank and will run that through just because  Otherwise fingers crossed that it was just an air leak.
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