P0420 question

[pjk79]

I have been reading over and over the threads on the p0420 code as it seems to keep popping up on my car. Here is my question could a leaking valve cover gasket cause enough of a vacume leak to cause this code?

[grossgary]

that would be weird.

personally i'd install the $15 inserts on ebay first and hopefully you never have to see that code again. it's a complete waste of time, benign, meaningless, and a debacle for many manufacturers, not just Subarus.

[pjk79]

$15 ebay insert? What is it? and do I put it on the front or rear O2 sensor?

[grossgary]

rear

remove sensor, install this part, then reinstall sensor.

just an example:
O2 Extender Oxygen Sensor Spacer HHO Test Pipe 1 | eBay

there are different lengths and even right angle versions if you need more clearance (will vary by year/model/heat shields...stuff). some folks use two of the shorter ones piggybacked together if one doesn't work.

friend of mine that owns a shop said he's been using the right angle versions as they don't make the sensor + extender so long that they run into things. but i haven't tried the right angle style yet.

it's so easy to do and works so often that i consider this the first step unless there's some compelling reason to work on something else.

[richinlodi]

Originally Posted by grossgary

rear

remove sensor, install this part, then reinstall sensor.

just an example:
O2 Extender Oxygen Sensor Spacer HHO Test Pipe 1 | eBay

there are different lengths and even right angle versions if you need more clearance (will vary by year/model/heat shields...stuff). some folks use two of the shorter ones piggybacked together if one doesn't work.

friend of mine that owns a shop said he's been using the right angle versions as they don't make the sensor + extender so long that they run into things. but i haven't tried the right angle style yet.

it's so easy to do and works so often that i consider this the first step unless there's some compelling reason to work on something else.

Hey do you know if that one you posted will fit an '08 2.5?

[grossgary]

Originally Posted by richinlodi

Hey do you know if that one you posted will fit an '08 2.5?

well you should do a little research but all O2 sensors have the same thread pattern as spark plugs...been that way since like the 80's...probably 70's....so O2 sensor threads are rather standardized...that type of part fits like every subaru made for decades so i'm assuming yours too - but you should check, i haven't installed on on a vehicle as new as 2008 (but I'd bet a lot of money it's the same).

the main issue is making sure you have clearance...install this extender, then screw your O2 sensor into it - the sensor + extender will be longer - so if your 2008 has zero clearance behind the O2 it won't physically fit....then you get the right angle versions, which a friend of mine who owns a shop has started using exclusively for that reason.

doing the brakes on a 2009 tonight i'll have a look and see what kind of clearance the rear O2 has.

[cardoc]

Originally Posted by pjk79

I have been reading over and over the threads on the p0420 code as it seems to keep popping up on my car. Here is my question could a leaking valve cover gasket cause enough of a vacume leak to cause this code?

Its not a VW, Audi, Porsche, BMW, Mercedes, Volvo, Caddillac or Saab. So
no, a valve cover leak will not cause a 420.

Read though here: P0420 Diag

The "fix" GG speaks of is of no use and when there is an issue arising that illuminates the MIL with a 420, you need to find what it is. The list is large, but its better to spend time finding the problem rather than spending money guessing or hiding an impending domino effect.

Just because it runs doesn't mean its running proper.