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Discussion Starter · #1 ·
Like the title says. I've been in the process of trying to resolve a reoccurring P0420 code. I attempt a fix, clear the code and wait to see if the light comes back on, takes about 2 weeks for it to come back usually.

We are looking to drive this car on a road trip soon. What's the risk, if any, in driving this car 6-8 hours a day with this code? Will I lose power and need to find a garage?

There are zero other symptoms, only the code.

Thanks in advance.


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nothing, its a nag code at best.

It will probably cancel itself once it goes through 3 drive cycles and then reappear under a odd circumstance of plain driving again.

how many miles ?

how many miles on the rear o2 sensor?
 

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Ok cool. 130k miles. I'm going to try and maybe replace the rear o2 sensor before the trip.


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do you got anything obvious like a loose exhaust before the cats.?

and what year and engine is this?
 

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Discussion Starter · #5 ·
Hmm. I don't think so. Many moons ago some of the heat shield around the exhaust nearest the oil filter was rattling. I through a long hose clamp on it to tighten things up thanks to a recommendation from a friend that did so on his Forester.

This is a 2011 2.5i premium 6MT. I just had the clutch done and the oil pan gasket replaced.


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My 2000 Outback has been throwing that code for about 5 years and over 80,000 miles with no negative effects. It also still passes inspection. I have a ScanGauge installed and I just press the buttons to clear the light as soon as it comes on, which is about every other day.
 

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if it's due to an exhaust leak, perhaps a little xtra CO could get in the cabin. But, likely not at speed so, don't sleep in the idling car I guess?
 

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Yeah driving on a p0420 won't hurt anything. Your gas milage might be slightly affected by the computer. But no actual damage will occur.
Definitely check the exhaust for leaks and such.
 

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Yeah driving on a p0420 won't hurt anything. Your gas milage might be slightly affected by the computer. But no actual damage will occur.
Definitely check the exhaust for leaks and such.
I have asked a few places about Po42o and gas mileage, did not get a definitive answer as to if the ECU makes a typical car pump a little more gas on that particular code.

I cancel it right away just so it is not staring me in the face,
and I would not want to get a 2nd or 3rd code on top of it with just the one dashboard check engine light if a scan tool is not running.
 

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So I know this is an old thread, but just in case anyone is reading this today, definitely do get your car checked with a 420 code. Its not a "nag code" and it most assuredly is not harmless (although it could be in some cases) if you continue driving. Depending on the reason for the code, the potential exists to set your engine on fire. Additionally, if you have a vehicle with multiple catalytic converters, you can destroy them all and end up with a much larger repair bill. Best to get advice from qualified mechanics and not from randos on an internet thread. If the engine is sputtering or misfiring, stop driving immediately.
 

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So I know this is an old thread, but just in case anyone is reading this today, definitely do get your car checked with a 420 code. Its not a "nag code" and it most assuredly is not harmless (although it could be in some cases) if you continue driving. Depending on the reason for the code, the potential exists to set your engine on fire. Additionally, if you have a vehicle with multiple catalytic converters, you can destroy them all and end up with a much larger repair bill. Best to get advice from qualified mechanics and not from randos on an internet thread. If the engine is sputtering or misfiring, stop driving immediately.
 
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