Light came on so i went to Autozone for a reading. Code came back P0420, catalyst efficiency below threshold - bank 1

 

possible causes:

 

1. rich a/f ratio

2. ignition system malfunction

3. faulty catalytic converter.

 

Is there anything i can check or do before i take it to the shop for their opinion?

 

It's a 97 legacy

Light came on so i went to Autozone for a reading. Code came back P0420, catalyst efficiency below threshold - bank 1

 

possible causes:

 

1. rich a/f ratio

2. ignition system malfunction

3. faulty catalytic converter.

 

Is there anything i can check or do before i take it to the shop for their opinion?

 

It's a 97 legacy

 

this is all too common and can be very costly to repair.

 

some say it is the cats and they need to be replaced with subaru cats. (600 - 1000$ repair)

 

some say it's the front o2 sensor and it NEEDS to be a subaru o2 sensor, not generic or after market. (~100$ part plus labor)

 

some have done both and still have the cel, and so they go to the "anti fouler" fix. search "anti-fouler" here. (cheap)

 

but you need to read up on each before you pay someone to fix it.

I am of the Front O2 sensor must be OE crowd to fix this. your car is old enough to need a O2 sensoor. Even if it is a cat (which 90% of the time it is not) you will need an O2 sensor anyway. Your car is old enough for it to need sensors.

 

 

How many miles on this car?

how is it performing?

 

 

nipper

Almost 180,000 on it. runs fine but seems to idle a little rougher than it used to. It needs an inspection in March and the check engine lite will make it fail. Does the anti-fouler trick make the light go out?

Almost 180,000 on it. runs fine but seems to idle a little rougher than it used to. It needs an inspection in March and the check engine lite will make it fail. Does the anti-fouler trick make the light go out?

 

 

If you are going to try a last ditch repair before actually giving an honest attempt to fix the car i am going to bow out. Antifouler (which I do not like as a repair, as it doesnt solve the problem, only masks it) is the last thing to try, not the first.

 

 

nipper

If you are going to try a last ditch repair before actually giving an honest attempt to fix the car i am going to bow out. Antifouler (which I do not like as a repair, as it doesnt solve the problem, only masks it) is the last thing to try, not the first.

 

 

nipper

 

You seem to be reading something i didn't write. I'm looking for options and you seem to be one of the better (best?) informed person(s) on this board. Since I'm not financially independent (hence the '97 subie) i would like to fix the problem with the smallest outlay of cash possible. The anti-fouler would only be done if i needed to pass inspection so i had more time to make my car happy again. Tell me the correct way to accomplish this and I'll listen. My wallet will then tell me if or when get the job done.

Dollar wise penny foolish.

 

The best way to solve this issue is replacing the front O2 sensor. Yes you can use a cheap antifolwer, but that is only a fix by moving the O2 out of the exhaust stream.

 

You asked if tha antifowler makes the light goes out, and by your followup it sounds like this may be the route you will take due to the high cost (compared to a fowler) of an OE O2 sensor. Since no one has really checked to see how this affects gas mileage performance (which your running a little rough can be caused by a bad O2 sensor) nor catalyitc converter life (which is not a cheap part), i do not recomend it for a front O2 sensor.

 

A shop may try to sell you a cat (the lazy-shops diagnostics).

 

nipper

Ok, what can i expect to pay for a front 02 sensor from subidoo? Is it somewhere i can get at without a lift? If it was the problem, will the computer reset the light or does it need to be done manually? Since i only paid $1900 for the car and don't have monthly payments, i guess i can afford to fix it.

Ok, what can i expect to pay for a front 02 sensor from subidoo? Is it somewhere i can get at without a lift? If it was the problem, will the computer reset the light or does it need to be done manually? Since i only paid $1900 for the car and don't have monthly payments, i guess i can afford to fix it.

 

the part om line is about 100$, retail (msrp) ~140$, at the dealer who knows??? the time is only about 1/2 hour max.

 

do it yourself and save.

 

http://www.subarupartsforyou.com/cp_partlistbymod.php?model=Legacy&subcat=Engine+Parts%2C+Sensor+O2&year=1997

 

part number 97 front o2 sensor = 22690AA290

 

 

https://www.chaplinssubarugenuineparts.com/oe_parts_cat.html

 

oxygen sensor, legacy, front

96-99 $139.95 $102.44 Order By Description.

Electrical - Powertrain control - Automatic transmission - Oxygen sensor oxygen sensor, legacy, rear

96-98 $139.95 $102.44 Order By Description.

Electrical - Powertrain control - Automatic transmission - Oxygen sensor

139.95 @ local dealer.

 

any tips or tricks to change this out?

139.95 @ local dealer.

 

any tips or tricks to change this out?

 

Buy it on line.

 

Use a good wrench or socket. use penetraiting fluid. You may get lucky and it may come right out.

 

nipper

My opinion is that doing the anti-fouler trick first is a great fit for some people and situations. I'm not a "one size fits all fan". Start cheapest and move you're way up. An unnecessary $150 does not help you out at all. If $10 fixes it, then in my opinion anything more is a waste of money in some cases and for some people. If the extra $100+ spent gains you nothing then I personally wouldn't care and wouldn't care if someone else cared. It's kind of like a pissing contest in those terms

 

The 0420 error code is such a PITA and an annoyance. For the shear fact that it causes discussions like this, is hard to diagnose and is so sensitive.

 

Now - I say that and I've got brand new Subaru OEM spark plugs in my cars for my own reasons, similar to Nippers - so I agree with him in theory, I just apply it a bit differently. I'm going to have them for a very long time (most likely) and will probably recoupe the costs anyway in gas mileage over time.

Let's see 10+ years old and PA - you might have rust to deal with.

 

If you replace the sensor, hit it with penetrating oil now and every couple days before you get the part right where it meets the exhaust. Then hopefully it frees up well. You'll need a big wrench - it's either 22 or 24mm to get it out. Probably best to get a 6 point assuming you have plenty of degrees to turn it, but mine is actually a 12 point wrench and it's always worked. In rare cases of bad rust I've used a pipe/monkey wrench to get them out.

 

Don't unscrew it too fast if it's hard to turn. Turn it, then go check your email or make lunch, come back and turn some more. If it's tight this allows it to cool down and not heat up, expand, and gouge the nuts out of the threads.

Do the penetrating oil for a few days as suggested, then when you're ready to take it out warm up the engine. The heat expands the exhaust pipe and makes the unscrewing easier. Oh, and it takes a 22mm wrench (at least it is through '95 and I doubt they changed the standard size.)

Do the penetrating oil for a few days as suggested, then when you're ready to take it out warm up the engine. The heat expands the exhaust pipe and makes the unscrewing easier. Oh, and it takes a 22mm wrench (at least it is through '95 and I doubt they changed the standard size.)

 

 

Do it cold., but do as he says.

The same reason you dont change plugs hot is the same reson you dont do this hot. Look at a hole in a bsquare block. Now imagin the block expnading 1/8 of an inch (exagerated to make it easy to visualize). The hole will get smaller. Now put somthing in that hole and heat it all up. The hole will get smaller and thing in it will expand.

That theory is wrong Nipper.

 

If you have a hole in something(a washer say) and you heat the washer the hole in the washer will behave the same way as the material that is not there would have behaved, so the hole gets bigger.

 

Think about fitting a ring gear Nipper. What do you do? What happens?

 

The only exception is if you have a large block of metal and you only heat it locally around or near the hole, then the material can distort and expand into the hole due to being hemmed in by the cold and unexpanded material..

That theory is wrong Nipper.

 

 

The only exception is if you have a large block of metal and you only heat it locally around or near the hole, then the material can distort and expand into the hole due to being hemmed in by the cold and unexpanded material..

 

 

Like an O2 bong, or an exhaust pipe?

 

I am aware of the physics behind the washer

http://physics.kenyon.edu/EarlyApparatus/Thermodynamics/sGravesandes_Apparatus/sGravesandes_Apparatus.html

 

But here the O2 sensor and the SS exhaust probably have the same expansion properties. Heating a nut usually works better then heating a bolt mounted into something.

 

In order to get the O2 sensor hot enough to move, if going that route, I would STRONGLY suggest a flame as oppsed to a hot exhaust pipe.

Sorry nipper, but in practical terms . . . it works!

Let's see 10+ years old and PA - you might have rust to deal with.

 

Hopefully it will be in the same shape as the rest of the car with little rust at all.

 

(yea, i know, keep dreaming)

Hopefully it will be in the same shape as the rest of the car with little rust at all.

 

(yea, i know, keep dreaming)

 

sweet, awesome! yeah somehow my 1996 Legacy Lsi is rust free, it's absolutely spotless and was a one owner car from Pittsburgh go figure.

Finally bought the sensor and it says bosch. Is that true subaru OEM? Can i buy the same thing from a parts store if they sell Bosch?

Can i buy the same thing from a parts store if they sell Bosch?

 

I say yes. Others may disagree, although I've yet to hear a logical explanation of why.

 

Bought a Bosch universal on Amazon recently, $42 with free shipping.