Car is throwing a Catalytic converter fault

[2008Liberty]

Hey all,
Car has thrown a fault twice now!
Both times my engine light has come on and cruise control light has been flashing!
After having it scanned i believe it has given a po420 code which is the "catalytic converter low threshhold sensor"
Just wondering if anyone has had this problem before and how much it cost them?
Car is going into subaru today so im preparing for a expensive fix, but im still curious to know if people have come across this before!:)

Thanks
Scott

[KiDo_Tuning]

Hey all,
Car has thrown a fault twice now!
Both times my engine light has come on and cruise control light has been flashing!
After having it scanned i believe it has given a po420 code which is the "catalytic converter low threshhold sensor"
Just wondering if anyone has had this problem before and how much it cost them?
Car is going into subaru today so im preparing for a expensive fix, but im still curious to know if people have come across this before!:)

Thanks
Scott

You have an aftermarket exhaust fitted? I can disable the CEL with a reflash, whcih is the only permanent fix

[2008Liberty]

Yeah i have but it's a catback system and found out today that my cat is burnt out on the inside...

Needs replacing!
A casual $3000 quote from Subaru is what I got...


Performance highflow cat for $500 at my local muffler shop is my new option:)

An excuse for a performance modification aha!

[KiDo_Tuning]

Yeah i have but it's a catback system and found out today that my cat is burnt out on the inside...

Needs replacing!
A casual $3000 quote from Subaru is what I got...


Performance highflow cat for $500 at my local muffler shop is my new option:)

An excuse for a performance modification aha!

New high flow cat will trigger the code more often

PS: That price is high, new high performance metal cat is about $200 plus about $100 to fit

[2008Liberty]

Yeah i also heard that i highflow cat will trigure it which i dont want either.
just assessing all my options really.. i would assume its possible to just get a cat off a subaru liberty from a wrecking yard and have it fitted?

Anyones thoughts please let me know! 3000$ is rediculous to be spending on a cat thats only purpiose is to mnake my car a "greener" car

[KiDo_Tuning]

Yeah i also heard that i highflow cat will trigure it which i dont want either.
just assessing all my options really.. i would assume its possible to just get a cat off a subaru liberty from a wrecking yard and have it fitted?

Anyones thoughts please let me know! 3000$ is rediculous to be spending on a cat thats only purpiose is to mnake my car a "greener" car

2nd hand would be fine, easier to just turn the code off though haha

[2008Liberty]

as in permanantly off? like disabled or will it fix the problem?
if my cat is actually blocking up and i turn the sensor off then im asling for trouble down the track surely?

[KiDo_Tuning]

as in permanantly off? like disabled or will it fix the problem?
if my cat is actually blocking up and i turn the sensor off then im asling for trouble down the track surely?

Yes, the CEL can be turned off permanently, same way the turbo guys have theirs turned off

Your cat is not 'blocked' it is loose/inefficient so the rear O2 sensor behind the cat is getting hotter, which is what throws the code. Hence why the code is often thron with a high flow cat, the extra flow lets more heat through and the rear O2 sensor throws the code

[2008Liberty]

Whats the likelyhood of the rear 02 sensor being faulty?
subaru said its not likely at all, but past experiences have told me to replace 02 sensors and the problem was sorted..
so it could just be my 02 sensor right?

[KiDo_Tuning]

Whats the likelyhood of the rear 02 sensor being faulty?
subaru said its not likely at all, but past experiences have told me to replace 02 sensors and the problem was sorted..
so it could just be my 02 sensor right?

Not the sensor, the heat is the issue from failing cat. It is a common issue with aftermarket exhausts, put the stock exhaust back on and I bet you never have the issue again

[2008Liberty]

my aftermarket exhaust is a catnack system... so nothing to do with my cat or anything at the front of my car...

So either the cat is buggered or a sensor is..

[KiDo_Tuning]

my aftermarket exhaust is a catnack system... so nothing to do with my cat or anything at the front of my car...

So either the cat is buggered or a sensor is..

I knew you had an exhaust fitted. The P0420 code is caused by Failing a Catalytic Converter Efficiency Test and is triggered by increased gas flow heating the cat, and the rear O2 sensor getting hot(Logic in the ECU dictates that)

What I am getting at is if you clear the code ater putting on a stock catback, the code wont appear again even if the cat and O2 sensor are not changed. Yes, you can fit a new or used cat BUT it is likely that within the next 6 months the code will appear again.

Also, the code would have flicked on while cruising at a constant speed right?

[2008Liberty]

Yeah i was cruising in 5th at 100 kms/h all three times it has triggered...
IF you are correct, why would my catback system be causing this?
subaru told me that my catback exhaust is irrelvant to this code..

Really confused with this fault... and very keeen to get it sorted!

[zch91]

I wouldn't trust most subaru dealers.... Matt definitely knows his shit. That's my 2c.

[XT_for_me]

The Cat back exhaust will lower back pressure and allow more gas to flow through the stock cat, hence the rear O2 sensor is getting hotter than it will with a stock exhaust. This is a really common problem, and the easy permanent fix as Matt said is to disable the CEL in the ECU