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Another P0420 CEL post...


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Posted

So our 05 2.5i (stock), has thrown three P0420 codes in the last 6-8 months. First one was cleared, and came back about 4-5 months later... So we thought it was a bad tank of gas, etc. Second one was cleared, and it has now come back for the third time, just about a month or so later. Can't be three bad tanks of gas.

 

So, since it's all stock... Where should i begin? 05... 88k miles or so. Original CAT. Original O2 sensors.

 

Seems like the consensus is to replace the downstream/rear o2 sensor, and start there? Sounds plausible, and also the cheaper of the two sensors...

 

THoughts?

 

thnks

Posted
Well stock cats are designed to last the life of the car however the don't :) you can replace the sensor first if you get P0420 MIL again time to replace the cat-pipe. The sensor reads the composition of the gases flowing past it. You can get that cat section for under $300 NOT from Subaru
Posted

Sounds good...

 

Would a fault in the rear o2 sensor do anything to the gas mileage.. mpg seems to have deteroirated over the past year or so.

Posted
Sounds good...

 

Would a fault in the rear o2 sensor do anything to the gas mileage.. mpg seems to have deteroirated over the past year or so.

 

yes however the front sensor controls AFR's it may be sensing a rich or lean condition coming from upstream (the actual cylinders) OR it has failed and is throwing the timing/firing of causing the rich or lean condition. See how this is a revolving door ???? However it is best to start at the sensors and cat first then reset the ECU (take off red terminal pump brakes turn on lights beep horn etc anything to use up stored voltage in the system) re connect red terminal turn key to ON DONT START! Let the fuel pump prime and the throttle position sensor calibrate ( this takes about 10 seconds) then start

Posted

Will do. Ordered up the o2 sensor, and should hopefully have by today or monday! I will report back.

 

Thanks for your help.

Posted
this thread must be contagious guess what happens while driving today? P0420 :lol: pulled the code says its bank 1 cat deficient blah blah. Where did you get your rear sensor and how much was it ?
Posted

Before i order I will test the connections about 5 months ago same thing happened checked the rear O2 plug and one of the wires had backed out of the plug like it had a bad retainer or something. If that doesn't solve it ill swap it out it has 60K on it anyway could stand to be changed.

 

 

Thanks :)

Posted

Dealer wants $167.00 for the post-cat (grey) and $187.00 for the pre-cat (orange) plus .5 hour install for both @ $125.00/hr

 

Well now that I have my Monday laugh, resulting from yet another stealer quote, I can continue with my day.

Posted

wow... i will take the 10 minutes and 63.00 bucks and do it myself !

 

$230.00 is nuts. Looking at some of the forum posts, ppl have been quoted EVEN HIGHER! insanity.

 

What is even more troubling, is the inconsistency in quotes from various subie dealers.

Posted
wow... i will take the 10 minutes and 63.00 bucks and do it myself !

 

$230.00 is nuts. Looking at some of the forum posts, ppl have been quoted EVEN HIGHER! insanity.

 

What is even more troubling, is the inconsistency in quotes from various subie dealers.

 

 

AGREED!

 

The stealers quote low and high ( but still all higher than other outlets). Sad part is some people just take it up the anus or don't care. I can afford the parts and labor easy that is never the problem but when you can find the EXACT same part for $104.00 cheaper I can't go along with such a load of shizzle.

 

If only somebody could get a load of XM/SIRIUS modules and sell them at 50% of stealer cost :lol:

Posted

LOL agreed!

 

The only reason to hit the dealer is those darn subie bucks! typically makes for a cheap maintenance program!

Posted

replaced the rear o2 sensor. a bit tougher than i had anticipated. This thing was ON THERE!!!!

 

i hit it with PB Blaster 4 or 5 times... and used an o2 wrench. It finally went when i used my jack handle as a breaker bar extension.

 

now, we'll wait and see if the 0420 code comes back....

Posted

Thats interesting... even if it cleared up, i thought you would need a code/battery reset to clear it out.

 

I guess the ecm could have figured it out, but i would think that it would have needed a good amount of start cycles before it cleared out.

  • 3 weeks later...
Posted
so the P0420 code came back after the rear o2 sensor replacement... ANy chance its the front sensor?? Or is this basically a Cat Convertor job?
Posted

Nice!

 

However, my CEL came back on after i did the rear 02 sensor... From what i gather - the front 02 sensor wouldnt be throwing 0420 code... Right? So that means, i move on to a CAT replacement at this point?

Posted
Nice!

 

However, my CEL came back on after i did the rear 02 sensor... From what i gather - the front 02 sensor wouldnt be throwing 0420 code... Right? So that means, i move on to a CAT replacement at this point?

 

 

Yup that rear O2 is nothing more than an annoyance it sniffs and says YAY or NAY.

 

If you have a bad cat that is going to be expensive as a replacement manifold from Subaru is over $600 :( but if you have a 05 it wont be nearly as bad.

Posted

so, there is a left and right cat on our 05... UGH.

 

which led me to do more research, and alot of ppl seem to think that the upstream o2 sensor can lead to the p0420.

 

Now im thinking, perhaps i should the upper sensor, before i spend $500 for the driverside and p/s side cats (total)...

 

oh, btw - Dealer wanted about $1800 for both sides... WITHOUT labor.

Posted
so, there is a left and right cat on our 05... UGH.

 

which led me to do more research, and alot of ppl seem to think that the upstream o2 sensor can lead to the p0420.

 

Now im thinking, perhaps i should the upper sensor, before i spend $500 for the driverside and p/s side cats (total)...

 

oh, btw - Dealer wanted about $1800 for both sides... WITHOUT labor.

 

 

Oh Oh Oh you have that massive manifold :( you are unlucky I forgot that that could be a possibility for your 05ers you have a manifold that is very long and in two odd piece that unbolt right past the passenger side primary.

 

If you get a chance look under you car and count the sensors I think you guys have three one on each primary and one near the rear flange. You could convert it to the other style 2005 layout which is wayyyyy cheaper

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