p0420

[dusterbd13]

i keep getting this code. my assumption is a bad downstream 02 sensor, but i want to run diagnostics before spending money. what diagnostics should i run? where can i find the flowcharts for this code? thanks for any help you can give me.

michael

[SubaruDriftBoy]

PO420 *Catalyst System Efficiency Below Threshold

this means for my car (2000 BE GT LTD) that the gas i had put in wasnt good or something like that, if you take it to a dealer they can clear it or any place that has an OBDII checker they can erase it for you. i never had a problem doing it myself in my car so you shouldn't have a problem either. and for future reference, there is a sticky of all the OBDII codes relating to the legacy at the top of this section.

[Huffer]

i keep getting this code. my assumption is a bad downstream 02 sensor, but i want to run diagnostics before spending money. what diagnostics should i run? where can i find the flowcharts for this code? thanks for any help you can give me.

michael

Are you serious? Did you even search the forum or the threads? At least you got the right section...

Do some reading, and check this link:
http://www.obd-codes.com/p0420


A code P0420 may mean that one or more of the following has happened:

* Leaded fuel was used where unleaded was called for
* An oxygen sensor is not reading (functioning) properly
* The engine coolant temperature sensor is not working properly
* Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
* Retarded spark timing
* The oxygen sensors in front and behind the converter are reporting too similar of readings

[dusterbd13]

so maybe o should have sone a little better on the first post, but i didnt. ill try again.

and yes, i ahev searched the code fror the catalytic converter efficiency, and found that it may be caused by o2 sensors, bad cats, out of range on the air fuel ratio, or a burp on the omputer. i checked the codes and the history codes. no other codes. when cleared, this one usually returns after about 50 to 100 miles. the car runs like usual, but the fuel economy is all over the map with the same driving style in the same environments. averages go between 25 and 21 mpg.

the car does have a rough idle when in gear and warm, but not in neutral or cold. does not smell rich from the enhaust, and the plugs are fresh. has hesitation right off idle wigh i attribute to the torque converter taking a little to get the car moving. after foghting a tps sensor on my crx, i am now rethinking this.

what i am aking for is the diagnostics for figuring out what may be causing thsi code, and where to start checking before spending money on things that are not casuing this. i know the hondas have a whole flow chart of things to check when the codes are set, and im assuming that subies are the same way.

so hopefully that clears up the conception that im a non searching and or illeterate dumbass. i shoudl just know better tahn to try to type a clear and soherent post after working a double.

michael

[Huffer]

^^ that post definitely helps. The MPG is the big one for me - if you are getting P0420 and bad mileage, then I would look at replacing BOTH O2 sensors. Most people only replace the rear, and then replace the front one a few months later. I say do them both now.

[dusterbd13]

what are the diagnostics on the 02 sensors? ohms, etc for them. that way im not throwing money at this thing, cause i dont HAVE money to throw at this thing. financial setbacks suck.

Michael