I keep blowing a p0420 code from my ecu, my scanner tells me its from (bank 1) cat inefficiency. my car is a 96 lego and has 2 O2 sensors. does anyone know if the (bank 1) is referring to the front or rear O2 sensor? my scanner refers to the front as (bank 1) and rear as (bank 2) in monitoring modes.

I'm having the same problem. Replaced the sensor but the code has returned so there is something else causing the problem. thinking I may need to have the injectors cleaned.

I post here from time to time that I've had pretty good success with Seafoam curing this - atleast for a while.

 

Search for the procedure. Makes a cloud of white smoke - your neighbors will think your house is on fire.

 

I've done it to several Subaru's and know the light didn't come back on for atleast several thousand miles.

 

I've taken to doing it to other cars now as well with actually pretty good success. It's not like cats are cheap to replace.

I'm having the same problem. Replaced the sensor but the code has returned so there is something else causing the problem. thinking I may need to have the injectors cleaned.

 

did you also replace the catalytic converter with the sensor(s)?

 

which sensor did you replace? front or rear? is your cat single or dual sensor?

Replaced the cat a few years ago and have since replaced the front sensor twice. Engine currently has about 230K. Seriously thinking about selling the car and upgrading to something newer with less mileage.

System had two sensors. Both were replaced when the new cat was installed.

does anyone know if the (bank 1) is referring to the front or rear O2 sensor? my scanner refers to the front as (bank 1) and rear as (bank 2) in monitoring modes.

 

Bank numbers refer to the sides of the engine. Bank 1 is on the side of the engine with cylinder #1 so bank 2 is on the other side of the engine. The sensors can be refered to as 1 and 2 also and 1 would be the front and 2 would be the rear sensor.

I was blowing cylinder misfires, temp sensor codes ans P0420's for two weeks. I repaced the temp sensor, replaced the NGK plugs and Subaru plug wires and no codes for a month. Also picked up 4MPG

 

Replaced the cat a few years ago and have since replaced the front sensor twice. Engine currently has about 230K. Seriously thinking about selling the car and upgrading to something newer with less mileage.

System had two sensors. Both were replaced when the new cat was installed.

this code is a debacle John - have you seen the $5 spacer fix? it works nearly every time.

 

if it was an aftermarket converter that could be the issue...but nonetheless the spacer trick will fix it.

 

i have a few spacers (this issue is common across many vehicles, not just subaru's) and can send you one. shoot me an email if you do and i'll drop it in the mail.

w0rd that spacer fix looks interesting! do you know if the ecu monitors the rear 02 for anything other than cat efficiency? I know the front has a lot to do with gas millage does the rear have any part in the ecu fuel calculations?

I do Seafoam first, then the spacer if needed myself.

 

 

I may be lucky but one or the other has fixed every one I needed to fix.

dave - i'll try some seafoam.

 

i've cleared them and had them not come back (the last one i did on a friends honda has not come back yet). have you sea-foamed any there were known to be recurring and return every time the code was cleared?

 

w0rd that spacer fix looks interesting! do you know if the ecu monitors the rear 02 for anything other than cat efficiency? I know the front has a lot to do with gas millage does the rear have any part in the ecu fuel calculations?

 

the rear sensor has nothing to do with anything except that emissions monitoring for the efficiency. it can not affect driving or gas mileage, it's not used. you can completely unplug it if you want and it doesn't change anything - just gives you a check engine light.

 

not only that - but even when the code is showing the vehicle would still pass an actual emissions test by the numbers.

 

it's benign in every way - the tolerances in the code are impractical.

 

it's sad to hear all the stories locally and see all the threads in subaru (and other - this is affecting other manufacturers too, not just subaru) forums on this issue with folks spending hundreds and thousands on converters, sensors, OEM converters...and for a completely benign code???!!!!

 

so - it's for "emissions" - maybe they should calculate all the waste, byproducts, resources burned to build, fabricate and support all the unnecessary parts and repairs caused by this dumb !*(&!#*$&(*$ code.

 

that sounds really "green" doesn't it? ????

Edited March 27, 201214 yr by grossgary

there are laws that make them do that kind of stuff..... and people only fix those issues because unless you have an unscrupulous smog tech they will not overlook a check engine light. that's going to be a pretty greasy palm if you ask me! I'd rather take measures to prevent it rather than replace sensors and parts. but if I were a little old lady or someone not able to get under a car it makes sense that its there. we forget cars are made for the masses that don't even open their own engine bay....