P0420 code 2011 outback H4

[bluebird]

I have a 2011 outback 2.5.  Today a bunch of lights came on; check engine, traction control, brake light flashing and cruise control.  I pulled the codes and got the P0420 catalyst system below threshold Bank 1.  I've seen some stuff online about it but wanted to get the experts here to weigh in.  If the idea is to replace an O2 sensor would it be the rear one or the front one?  Are both of the parts the same?  And there was mention of a spacer.  What is that about?  Could also be the cat convertor and lots of other things as well.  Where should I start?

 

any help much appreciated

[brus brother]

A number of the tricks like the spacer don't work on 2005+ models.

How many miles do you have on the car? There is a separate warranty on emission items. I can't remember the time/mileage limits.

What is the maintenance history on the car?

My 2005 has had the code for over 70K miles.

When you get a CEL, numerous lights will show on the dash and systems like cruise control become deactivated.

In my case, after changing the front sensor and working through the symptoms with cardoc on the subaru outback forum, I just bought a $20 code reader and clear the code every two years to pass inspection.

The car runs a little wonky after clearing the code as the computer relearns. 

The light occasionally goes out on its own which seems to indicate that the car is just over the "threshold."

Car performance and gas mileage are unaffected.

Edited May 27, 2017 by brus brother

[bluebird]

Thanks for the reply.  Sorry I should have mentioned the car has 143,000 bought it used about a year ago and have the records.  all maintenance  was done at a dealer and all the interval checkups were done. If this were my car I would take your approach, I like the way you think, but it is my wife's.  She is convinced that the brakes will fail due to the flashing brake light and that the wheels will fall off due to the traction light. 

So if I can fix it by replacing an O2 sensor I would do that.  How hard are they to get off on this car.  I did one on my 2003 outback and it was a challenge to get to. If it need a new converter not sure what I will do but I have read that this code is rarely triggered by a faulty converter.

[brus brother]

Common cause of P0420 is an exhaust leak but mine had none.

Spray the cold sensor with some PB Blaster.

When trying to remove the sensor, do it after the engine/exhaust has warmed up.

Autozone will lend the O2 sensor removal wrench. If you can extend the length of the handle with a piece of pipe, the longer the wrench will give you more leverage.

Edited May 28, 2017 by brus brother

[keith3267]

One common cause is the gasket between the exhaust manifold and the head pipe (exhaust pipe).  But I have fixed most of mine by replacing the rear O2 sensor.  One time I had to replace the front sensor too.  Also try some fuel injector cleaner and use top tier gas for a while.  Not premium, just top tier.  Costco gas is a top tier gas as is Exxon/Mobil.

[bluebird]

I cleared the code yesterday and drove the car maybe 120 miles since then.  No lights have come on yet.  I'll just see how it goes for now but will try some FI cleaner and Costco gas.  If I get the code again I guess I'll try the rear O2 sensor.  Many thanks for the help

[1 Lucky Texan]

seems like a 'legit' error code but, the cars can be sensitive to voltage issues and a weak battery can set 'spurious' codes.

 

even though cat. conv. is in the definition of the code, MANY times the converter is fine the issue is elsewhere as described above.

[GeneralDisorder]

You can check cat operation with a thermal imaging camera. Chances are you will need a new exhaust header/cat. The cat should be about 100* F higher on the outlet than the inlet if you hold the engine about 2500 RPM.

 

Throwing sensors at it is mostly likely a waste of money. The ECU can detect bad or slow sensors. If it's decided the cat is bad it means it's seeing the secondary O2 signal cross counts are too high. Sensors fail to slow, not fast response.

 

GD

Edited May 29, 2017 by GeneralDisorder