Check Engine Light P0420 - Subaru Outback - Subaru Outback Forums
Reply
 
LinkBack Thread Tools Rate Thread
post #1 of 19 (permalink) Old 05-14-2012, 07:43 PM Thread Starter
Registered User
 
Join Date: Dec 2011
Car: 2001 Outback LL Bean
Posts: 57
Feedback Score: 0 reviews
Check Engine Light P0420

My check engine light has been going on and off for 2 years. I have owned the car for 2.5. My local mechanic wants to install new catalytic converters. I took it to another shop for a 2nd opinion, 6 months ago. They suggested upstream O2 sensor (one of the 2) was bad and I let them replace it. Light went off for a little while, but not long (maybe 6 weeks). Now it is back to doing what it was doing before I took it in the first time. It'll come on for a week or less and then be off for a couple of weeks or more.

I'm pretty sure that the original code was the dreaded P0420 and this is what's still indicated. At the same time they replaced the O2 sensor, there were some non-OEM exhaust modifications subbed out to a muffler shop. The work looks fine and I'm not entirely sure how it differs from factory, but thought I should mention it.

I have purchased a PCV valve and will try to get that installed soon. Have read that can be one culprit.

Does anyone think this can be cats? It seems like the frequency and duration of the CEL is not getting any worse.

What else should I try? Should I take the car back to the shop that did the O2 and exhaust mods and ask them to check it out again?

Thanks!
kclaus is offline  
Sponsored Links
Advertisement
 
post #2 of 19 (permalink) Old 05-14-2012, 11:33 PM
Registered User
 
Join Date: Jun 2005
Location: Waterbury, VT
Car: 2006 and 2000 Outback Wagons
Posts: 43
Feedback Score: 0 reviews
My wifes 2000 OB has had the P0420 code for about 2 years now. It seems to come on at random times. Sometimes it might be twice a week and other times it might be twice a month. I have a ScanGauge in the car so I just use that to clear the code as soon as the light comes on.

The exhaust is in good shape. The engine runs great and gets great gas mileage. It passes PA State inspection including emissions. So, that tells me there is nothing wrong with the catalytic converters. I keep the engine well tuned - fresh oil, air filter, new PCV valve, new plugs, new plug wires. Both the front air/fuel sensor and the rear oxygen sensor were replaced with genuine Subaru parts about 2.5 years ago.

As long as the car continues to run well and pass inspection and emissions I am not going to worry about the code.
cagranitz is offline  
post #3 of 19 (permalink) Old 05-15-2012, 12:24 AM
Registered User
 
Join Date: May 2009
Location: WV
Car: OBW H6 VDC, H6 OB Sed, XT6's
Posts: 5,695
Feedback Score: 1 reviews
during the exhaust work - do you know if any of the sensor locations were moved? doubtful - sounds like all the work was around the muffler?

no exhaust leaks?

do not replace your converters - Subaru converters do not fail unless they are abused - most 1980's Subarus still have the original converters and pass emissions. rust gets them, that's about it. but they're so robust compared to aftermarket i simply weld the rusted flanges back on to avoid going with aftermarket or sick $300 - $600 dealer prices.

the best fix is to simply install the $5 spark plug non-foulers on the rear O2 sensor and be done with this gremlin. it's not an actual issue - more like the tolerances for this particular data point are not realistic for real world applications.

the 0420 code doesn't affect engine performance *at all* - that rear sensor isn't even used by the ECU.

you could try to replace all the O2 sensors if you were gung ho to nail it down, i'd simply install the spacer for $5 and 15 minutes and be done with it.

H6 VDC OBW, H6 OB Sedan, XT6's, castrated LSi - FWD EJ18
grossgary is offline  
post #4 of 19 (permalink) Old 05-15-2012, 11:25 AM
Registered User
 
Join Date: Nov 2007
Location: central NY USA
Car: 2003 LLBean H6 Outback
Posts: 4,421
Feedback Score: 0 reviews
I suggest using the anti-fouler trick after checking for vacuum leaks, bad PCV valve, exhaust leaks.
CNY_Dave is offline  
post #5 of 19 (permalink) Old 05-15-2012, 02:17 PM
Registered User
 
Join Date: Jun 2005
Location: Waterbury, VT
Car: 2006 and 2000 Outback Wagons
Posts: 43
Feedback Score: 0 reviews
In my case, I am avoiding the anti-fouler trick since I don't know if the car will still pass PA State inspection with that mod.

If the problem got much worse, then I would use the anti-fouler. I already have the parts needed just in case

I have seen most people mention getting the anti-fouler from the "Help" products sold by Pep Boys, AutoZone, etc., but apparently these are prone to rapid rusting. I thought I have seen someplace on the web that sells a stainless steel version that should last much longer.
cagranitz is offline  
post #6 of 19 (permalink) Old 05-15-2012, 03:28 PM
Lord of ScoobyMods

 
Peaty's Avatar
 
Join Date: Jan 2004
Location: Lawrence, Kansas
Car: 01' OB Wagon / 13' OB CVT / 10' Legacy 3.6R / 99 Mita MX-5
Posts: 1,177
Feedback Score: 0 reviews
We have a 2001 OB wagon in the family, my son's. We had the code pop up too. It was strange in that when he was driving around town it would never occur. Only after a long trip (~1+ hrs), on the way home (after being parked) the code would appear. The code is from the rear senor but I changed both front and rear at the same time. I figured at 200K miles it was time anyway. Well, after the next long trip the code popped up again. I have a code reader and I've cleared the code a few times. I inspected the cat and whole system and could not find a leak. We don't have any state inspection here in KS so I went and installed the anti-fouler bits. So far it's been code free even after about 4 long trips that I'm pretty sure would have set the code off.

I just wanted to give my experience doing the mechanical fix. I've known about it for years but never had to give it a try. I have a page on the subject on Scoobymods here with some pics:

http://www.scoobymods.com/showthread...-cel-5468.html

quick quote from that link

Quote:
I decided to try the Mechanical fix for the heck of it. I looked at the location of the sensor and of course it was angled up into the tranny tunnel. There was not a lot of room. I went with the #42009 anti foulers because they came with crush washers and appeared to be a little shorter. That would give me more room. The #42002 version was a taper fit and seemed to be longer.

The fist trick was to drill the 1/2" hole in one of them. That was tricky. All I can say is you will need a vice and start with a smaller drill bit than 1/2" and work your way up.

Then I removed the old sensor and installed foulers on the sensor. I barely had enough room to get it installed but I managed. The wires were too close for comfort to the tranny tunnel so I had to use a BFH and a pry bar to give it a touch more clearance. I've taken two long trips and so far the code has not returned. So far so good.

Cheers,

Peaty

www.ScoobyMods.com
Peaty is offline  
post #7 of 19 (permalink) Old 05-16-2012, 09:05 AM
Registered User
 
DavidPeab's Avatar
 
Join Date: Apr 2012
Location: Pasadena, MD
Car: Little Red, 2000 Outback H4 "Limited"
Posts: 2,374
Feedback Score: 4 reviews
Mine comes on after driving in wet weather. I use my scan gauge to reset it and it stays off until I drive in the rain again. Recently passed MD state inspection - the thorough one needed to get a new registration. Perhaps water splashing up is seeping into 02 sensor seal. Old car, $20 scan gauge from Amazon or Ebay to reset. A small piece of electrical tape over the CEL works well too (Just kidding).
DavidPeab is online now  
post #8 of 19 (permalink) Old 05-16-2012, 02:46 PM
Registered User
 
Join Date: Feb 2012
Posts: 79
Feedback Score: 0 reviews
Quote:
Originally Posted by cagranitz View Post
In my case, I am avoiding the anti-fouler trick since I don't know if the car will still pass PA State inspection with that mod.

If the problem got much worse, then I would use the anti-fouler. I already have the parts needed just in case

I have seen most people mention getting the anti-fouler from the "Help" products sold by Pep Boys, AutoZone, etc., but apparently these are prone to rapid rusting. I thought I have seen someplace on the web that sells a stainless steel version that should last much longer.
The anti fouler trick is used on all makes and models ,and it works most of the time. In the california bay area they look for this with a mirror while checking your cats and you will fail smog if they see it. What state are you in and how rigorous is your inspection? I have used this on two different types of cars and it worked perfectly.

sam333 is offline  
post #9 of 19 (permalink) Old 05-16-2012, 10:13 PM
Registered User
 
Join Date: Jun 2005
Location: Waterbury, VT
Car: 2006 and 2000 Outback Wagons
Posts: 43
Feedback Score: 0 reviews
I am in Pennsylvania, and we have yearly State Inspection, but I don't know how picky they are about mods such as the anti-fouler on the O2 sensor.

At this point it's not enough of a problem for me to perform the mod, but if it got much worse, then I would definitely do it.
cagranitz is offline  
post #10 of 19 (permalink) Old 05-17-2012, 06:38 PM Thread Starter
Registered User
 
Join Date: Dec 2011
Car: 2001 Outback LL Bean
Posts: 57
Feedback Score: 0 reviews
I'm also in PA. My impression is that if the CEL is off, the car will pass emissions. I'm not 100% sure, but I don't think they even look at the actual emissions.
kclaus is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Subaru Outback - Subaru Outback Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



User Tag List

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Rate This Thread
Rate This Thread:



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome