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How screwed am I. P0420 code


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After watching some videos online this doesn't seem like something I'll be able to fix on my own.  The car is a 2005 subaru legacy na with 89k miles.  I don't think the cat would be bad.  I also got a C0116 code.  Anyone know what that is?

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Drove my 05 OB with P0420 for over 100K miles after it first popped on. Car died a peaceful death around 225K. It's an emissions code.

Might come and go. Cruise will be disabled when the CEL is on. Get a cheap code reader if you think you might have other codes of concern. If you need inspection, there is a sequence of clearing the codes and getting enough systems ready to pass.

I was told the tolerances on emissions was so tight on that car that  it was easily over the limit.

I replaced O2 sensors and original cat (bank1) with aftermarket and code immediately came back.

Piece of black tape over the blinky dash lights and drove on.

Cardoc over on subaruoutback.org has a couple hundred pages of posts that try to solve issue but I never got to the point of success.
Stopped throwing my wallet at the car.

 

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4 hours ago, 1 Lucky Texan said:

an 05 could have bad wires in the 'gaiter' between the hatch and the body.

excellent point. I have a writeup here somewhere with pictures of that 'gaiter' with broken wires.

 

Video of someone with similar issue who decided to disassemble the rear gate innards.

I was lazy and just noted the broken wires, used a piece of dental floss (I'm a retired dentist) to pull the broken piece through the gaiter, tied on a piece of wire as a splice and dragged it back through and made the connections. I think there was a total of three wires that were gerschmucked and in need of handiwork.
Lasted until I canned the car.

Edited by brus brother
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yeah, broken wires in that gaitor is a pretty common thing.. the other half's 06 Outback had a whole bunch of broken/damaged wires. In his case, rear defrost quit working, rear wiper quit, and the license plate lights no longer functioned..

when we dug into it, obviously there were several that had completely broken, and a bunch of others that were barely hanging on... ended up reworking all of them.

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For me this code was my head gaskets.  The code was thrown when excessive coolant was being burned.  New had gaskets, code gone.  Hasn't come back. 

Do you have any other symptoms?  How do your spark plugs look? Is the top radiator hose hard after driving? car hard to start?  low coolant?  Loss of heat?  Erratic temperatures on the coolant temperature gauge?

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5 hours ago, Daskuppler said:

For me this code was my head gaskets.  The code was thrown when excessive coolant was being burned.  New had gaskets, code gone.  Hasn't come back. 

Do you have any other symptoms?  How do your spark plugs look? Is the top radiator hose hard after driving? car hard to start?  low coolant?  Loss of heat?  Erratic temperatures on the coolant temperature gauge?

Nope everything drives great.  Temp is right in the middle every time.  I ordered new plugs, pcv valve, coolant, air filter.  Going to change all that.  I did get oil change like 10 days ago and they overfilled it by like 1.5 inches on the dipstick.  Drove like 20 miles like that before it was drained.  I also filled up the tank maybe like 10 miles before the CEL came on.  Heard it could be bad gas.

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6 hours ago, evor1 said:

Nope everything drives great.  Temp is right in the middle every time.  I ordered new plugs, pcv valve, coolant, air filter.  Going to change all that.  I did get oil change like 10 days ago and they overfilled it by like 1.5 inches on the dipstick.  Drove like 20 miles like that before it was drained.  I also filled up the tank maybe like 10 miles before the CEL came on.  Heard it could be bad gas.

Yeah, it's kind of a catch all code. It's rarely catalytic converter though.

 

It's possible the overfilling on the oil threw the code as well. That's a lot of extra oil and I would be imagine you were burning quite a lot of oil which could throw the low efficiency code.  Maybe clear the code at your local auto parts store or disconnect the battery and see if no it comes back.

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8 hours ago, evor1 said:

Nope everything drives great.  Temp is right in the middle every time.  I ordered new plugs, pcv valve, coolant, air filter.  Going to change all that.  I did get oil change like 10 days ago and they overfilled it by like 1.5 inches on the dipstick.  Drove like 20 miles like that before it was drained.  I also filled up the tank maybe like 10 miles before the CEL came on.  Heard it could be bad gas.

1.5" high on the dipstick isn't that much over filled oil and not a big deal.  It's a 4.2 quart oil capacity, the shop probably added closer to the ubiquitous "5 quarts" which isn't enough to cause issues on those engines.  You got .8 quarts of free oil, I would have just ran it. 

Why did you drive 20 miles then check the oil?  Did you not want to check it before you left and be seen by them?

It's not "bad gas" - that's such a ubiquitous saying, like "check your gas cap", that people think it's far more common and wide spread than it is.  It's like assuming a hole in your yard was created by an asteroid instead of a squirrel, it's possible...sort of.   Many CELs are ripe for  "suspicion often creates what it suspects" or good old anecdotal thinking.  They treat the gas, change the windshield wipers, or wait until the next fill up and the light goes away so they magically assume it was "bad gas" or the windshield wipers.  When in reality the CEL was going to go away no matter what they did....and will likely return sometime in the next year. 

Just like yours will.  It'll most likely come back if it goes out. They do this routinely.  It's the norm. 

 

On 8/3/2022 at 2:13 PM, evor1 said:

After watching some videos online this doesn't seem like something I'll be able to fix on my own.  The car is a 2005 subaru legacy na with 89k miles.  I don't think the cat would be bad.  I also got a C0116 code.  Anyone know what that is?

First - you're definitely not screwed - you can drive the life oft he vehicle with that code one with no issues. It's immaterial to reliability assuming the car isn't puking oil, rusted to scrap, and overheating twice a week.  If you live in an emissions testing area or absolutely want that light off or need cruise control then you'll want to explore options but you're definitely not screwed. 

P0420 is tricky, no way to tell what tripped it.  your assumptions that it's not the catalytic converter have a great chance of being true.  

First steps are: 

1. Clear it and note how quickly it comes back - immediately, one week, a month?  Of course this can vary - it would come back immediately now but not come back for 3 months next time. But I like to do that for my first easy note taking. 
2.  verify absolutely NO exhaust leaks anywhere

3. do a tune up - you're already doing that, good job!!

After that the options vary depending on your objectives and goals but they can drive for the life of the vehicle with that code tripped.  It's not a big deal. 

 

 

Edited by idosubaru
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1 hour ago, idosubaru said:

 

Why did you drive 20 miles then check the oil?  Did you not want to check it before you left and be seen by them?

 

 

My cel came on while driving home so they had someone come check out the car. So he checked the oil and scanned it. Turned out to be p0174 due to the maf sensor connection being loose from them messing with the airbox to check the filter.  They had me go back to drain the oil a bit. 

 

I live in California so I got to pass emissions. How do I clear the code and system so that it can pass? I read just clearing the light isn't enough.   I just got my obd scanner tool so I'll clear it first and see how long it takes to come back

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24 minutes ago, evor1 said:

My cel came on while driving home so they had someone come check out the car. So he checked the oil and scanned it. Turned out to be p0174 due to the maf sensor connection being loose from them messing with the airbox to check the filter.  They had me go back to drain the oil a bit. 

 

I live in California so I got to pass emissions. How do I clear the code and system so that it can pass? I read just clearing the light isn't enough.   I just got my obd scanner tool so I'll clear it first and see how long it takes to come back

You will need to disconnect the battery and then drive the car for a couple hours to. Make sure all of the system checks are completed. If you disconnect the battery and drive straight to emissions, they can tell you did that and they will fail you.

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After you erase the codes, start the car without depressing the gas pedal. it will run rough as the computer relearns the car.
The first thing is to start the car and let it ideal for a few minutes. Nothing turned on and don't touch gas pedal. Let computer relearn the car. Best done with 1/2 tank of gas.
The sequence described in the video is what I remember but It might take a few tries.
I would try and plan on getting systems ready en route to test center.
As soon as you get monitors ready, get in line at emissions testing center!

Good luck.

 

 

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22 hours ago, Daskuppler said:

Maybe clear the code at your local auto parts store

parts stores will not clear the codes... they will only read them for you.

if you dont have your own code reader (and they are not that expensive anymore) then disconnecting the battery for about 30 mins is the way to go

 

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6 hours ago, heartless said:

parts stores will not clear the codes... they will only read them for you.

if you dont have your own code reader (and they are not that expensive anymore) then disconnecting the battery for about 30 mins is the way to go

 

Ahh okay, my local store used to just give me their code reader and let me do whatever I needed to. I did buy a code reader a while ago though so maybe that's changed.

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that po420 your car is stoned code sucks

ive been fighting it for 20 years on varios subarus i use a spark plug defouler inline with my 02 sensor i got mine at oreallys 

fixed it everytime i do need to remove it before smog though or it wont pass visual inspection

it still pops up every now and again and goes away it always comes on after a long down hill run coming out of the mountains to sea leval then a few day at a stable elivation the light goes off the car still has the original cats on it there over 20 years old and still working fine

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3 hours ago, ferp420 said:

that po420 your car is stoned code sucks

ive been fighting it for 20 years on varios subarus i use a spark plug defouler inline with my 02 sensor i got mine at oreallys 

fi

That doesn’t work on 2005+ legacy and outback’s due to changes in the ECU.

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1 hour ago, idosubaru said:

Autocorrect changed your message, you must have typed "imbecile" or "annoying", because it is.  2005+ leg/OB is also when you can no longer swap an engine/trans due to CANBUS.

well i could sware that the 06 outside had a defouler on both 02 sensors and it eliminated the po420 code but like you sead auto correct might have gotten me

 

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1 hour ago, ferp420 said:

well i could sware that the 06 outside had a defouler on both 02 sensors and it eliminated the po420 code but like you sead auto correct might have gotten me

 

My "autocorrect" comment was a joke trying to make fun of these asinine changes Subaru made.  the codes very well may have went away, I don't know enough about it to guess if it could have been the nonfoulers.  I've got some nonfoulers laying around and my 06 tribeca has P0420 but after all these years and 250,000 miles I don't think I want to touch the sensors....

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On 8/10/2022 at 7:33 AM, idosubaru said:

My "autocorrect" comment was a joke trying to make fun of these asinine changes Subaru made.  the codes very well may have went away, I don't know enough about it to guess if it could have been the nonfoulers.  I've got some nonfoulers laying around and my 06 tribeca has P0420 but after all these years and 250,000 miles I don't think I want to touch the sensors....

that po420 code was part of the reason we bought a hyunday

2000 is the newest i have now unless you count the entire drivetrain out of the 06 outback xt

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