Welcome to the North American Subaru Impreza Owners Club Friday March 29, 2024
Home Forums Images WikiNASIOC Products Store Modifications Upgrade Garage
NASIOC
Go Back   NASIOC > NASIOC Technical > Factory 2.5L Turbo Powertrain (EJ Series Factory 2.5L Turbo)

Welcome to NASIOC - The world's largest online community for Subaru enthusiasts!
Welcome to the NASIOC.com Subaru forum.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, free of charge, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join our community today!

If you have any problems with the registration process or your account login, please contact us.







* As an Amazon Associate I earn from qualifying purchases. 
* Registered users of the site do not see these ads. 
Reply
 
Thread Tools Display Modes
Old 04-26-2021, 08:44 PM   #1
_rgk
Scooby Newbie
 
Member#: 458787
Join Date: Nov 2016
Default P0420 and hard start

Hi folks, posting here because other Subaru forums seem to lack mechanical know-how.

2007 Forester N/A EJ25. Every once in a while it will have trouble firing on a cold start. Usually on the second try it starts.

Also once in a while, on a cold day, it would flash a P0420 cat code. I would clear the code and it wouldn't come back for a year or so.

Recently the cat code has been coming back consistently, but not all the time. The no-start issue seems to be correlated with the appearance of the code.

Any ideas? I know that typically a cat code is consistent with a bad cat, but the hard starting has me wondering. It just seems like more than a coincidence.

Otherwise the car has no issues. Front O2 sensor going bad, perhaps? Faulty injector or wire causing the cat to go bad?

Any ideas are appreciated. I have rebuilt engines and am mechanically inclined. Thanks.

Edit: Oh, I checked the O2 sensor voltage and found the voltage at the upstream sensor to be over 2 volts. The downstream sensor was 0.7 volts. Does that mean high oxygen (exhaust leak), or low oxygen (running rich, bad sensor)? My short and long term fuel trims are fine, in the low single digits, moving +/- around zero.
* Registered users of the site do not see these ads.

Last edited by _rgk; 04-26-2021 at 09:08 PM.
_rgk is offline   Reply With Quote
Sponsored Links
* Registered users of the site do not see these ads.
Old 04-26-2021, 10:42 PM   #2
Haevn
Scooby Specialist
 
Member#: 495950
Join Date: Jan 2019
Chapter/Region: South East
Location: Augusta, GA
Vehicle:
2011 WRX
WRB

Default

the cat might be clogged?
Haevn is offline   Reply With Quote
Old 04-26-2021, 10:59 PM   #3
_rgk
Scooby Newbie
 
Member#: 458787
Join Date: Nov 2016
Default

When I did the 105k service about 60k miles ago, I re-used the exhaust manifold gaskets. Just now I put in new gaskets. I just took the car for a spin and it has plenty of power. I will see whether the code comes back. If it does, I will replace the A/F sensor. At 175k, it's probably due anyway. If the code persists, I'll have a pretty good idea that it is indeed the cat.
_rgk is offline   Reply With Quote
Old 04-27-2021, 08:09 PM   #4
AliBenn
Scooby Guru
 
Member#: 487
Join Date: Nov 1999
Chapter/Region: TXIC
Location: Houston TX
Vehicle:
1998 /2005 STunIcorn
Acadia Green USDM 22b

Default

Screw new cats
Will trip code when cat operating below 90% efficiency

I have done this on 3 cars 3 diff manufacturers Same code
Code never came back


GL
AliBenn is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not 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
Forum Jump

All times are GMT -4. The time now is 11:12 AM.


Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2024 Axivo Inc.
Copyright ©1999 - 2019, North American Subaru Impreza Owners Club, Inc.

As an Amazon Associate I earn from qualifying purchases.

When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission
Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.