I have a 2005 outback llbean 3.0 with 146,000 miles.

Today the check engine light came on with a blinking cruise control light.

Had the code pulled at Advance which said P0420  Catalyst system efficiency below threshold

 

What is the fix?

O2 sensors? up or down stream is there a way to determine?  Best place to purchase and what brand?  I assume down stream by the wording of the code??

 

Suggestions are greatly appreciated.

 

I did replace the pcv valve about 1000 miles but not OEM.  Also I believe there are oil leaks around the valve covers that should be fixed.

 

Thanks in advance for your wisdom.

 

gerald in NC

2005 subaru outback llbean

HI,

This is a question that gets asked a LOT on all the Subie forums. Please do a little more searching to get more ideas than just mine:

 

- It could be the O2 sensors - I'd replace the front one regardless @ 146K...the rear one is not as important.

---I prefer to stick w/the name brands (but not from the dealer)...but Search on here for others' recommendations.

- It could be the CC - for the same 146K reasons. - but generally, if you bang on them and they rattle (not the heat shields) that's an indicator they're (going) bad.

 

 

 

 

 

TD

Edited April 14, 201510 yr by wtdash

general tune-up issues are good to address when chasing this. Followed by things like exhaust leaks or vacuum lines etc.

 

clear the code and monitor how quickly it comes back too. If possible, get freezeframe or, better, live data to see if fuel trims or other issues are out-of-line.

 

make sure there's no rodent-chewed or bad wiring. Refreshing ground connections is not a bad idea, etc.

 

the last thing you want to change, the cat conv., COULD be bad, but you want to be sure.

Cruise control blinks and is non functional when the check engine lite comes on.  Fix or just clear codes and cruise unit should function normal. As far as the o2 sensor goes, it usually ends up being the front  or upstream one that throws a code. Live feed would be the best way to diagnose this but that is usually not a free option.

How long since the last full tune-up? Spark plugs, filters? I recommend Subaru OE PCV valves because of problems with aftermarket brands.

 

Oil leaks won't cause this code unless the oil is getting on the O2 sensors or their wiring.

one obd2 Bluetooth adapter, one android based phone or tablet, and the torque app from the playstore.

 

Then you have live read. The obd2 adapters are about $10 on amazon.

Thanks to all, I will begin the chase.  I changed the plugs, OEM, less than 20K ago so should not be the problem.  Will try the connections, filters etc.  Did disconnect the battery to reset the code and cruise is working.  Will see how long it takes for the Check engine light to return.

 

Don't know about all, but the search function, for me, is of little use.  The function turns up very little of the vast information out there.

 

gerald

I changed the O2 sensors and problem corrected.  While under there I changed all O2 sensors and the oil cooler O ring.  

 

Thanks again for all your help.

 

Monk

I changed the O2 sensors and problem corrected.  While under there I changed all O2 sensors and the oil cooler O ring.  

 

Thanks again for all your help.

 

Monk

Please keep us posted if ever the p0420 returns.