The Mighty P0420 code

[HeathyVT]

Here is the deal bought my legacy at auction, since then I've had the exhaust replaced from the cat back, and front o2 senor, I replaced the knock sensor.

Car was code free for about 200-250 miles, then it set off the knock sensor p0325 code, and now the new one the p0420 Catalyst efficiency code. I had the check engine light cleared thinking maybe it was from me driving the car hard. So I babied the car and with in 30 miles my check engine light is on again. Does the p0420 indicate I should replace the rear o2 sensor? The car is completely stock, minus the studded snow tires:roll:

[williaty]

How many miles does the car have on it? It's always possible it actually needs a new cat.

[HeathyVT]

The car has 128,567 miles, kinda hoping it doesn't need a cat.

[williaty]

That's legitimately into new cat territory. On the early side, but definitely possible, especially if you've been running rich or burning oil at all.

I guess I'd say try replacing the O2 sensors, since that's much cheaper than a new cat, but you shouldn't really expect that to fix the problem.

[Draco-REX]

That's legitimately into new cat territory. On the early side, but definitely possible, especially if you've been running rich or burning oil at all.

I guess I'd say try replacing the O2 sensors, since that's much cheaper than a new cat, but you shouldn't really expect that to fix the problem.

Have you priced O2 sensors?? The one after the cat is a "paltry" $60 or so. But I decided to see what it would cost me to replace the front one since I think it might be making me a touch rich. $215!!! I said "F-it" I'll have Thorne tune around it.

[williaty]

Have you priced O2 sensors?? The one after the cat is a paltry $50 or so. But I decided to see what it would cost me to replace the front one since I think it might be making me a touch rich. $236!!! I said "F-it" I'll have Thorne tune around it.
Ouch. They're not that much for an RS.

Why not compare your front O2 to the LC-1, then adjust the front O2 scaling until they match.

[Draco-REX]

Ouch. They're not that much for an RS.

Why not compare your front O2 to the LC-1, then adjust the front O2 scaling until they match.

I might. It's not a whole lot; maybe 0.3 richer. My cruise oscillation seems to center in the low 14s.

[HeathyVT]

Well I would only need to replace the rear 02 sensor since I've already had my front one I had it done with the exhaust. The car doesn't burn any oil, and I've been getting 24-29mpg so running rich shouldn't be a option.

[Baja820]

healthyVT, looks like we are in the same boat.... My wifes 2002 legacy out back with the EZ30 did the same thing you described with your car. the local subaru dealer quoted me $1400 to replace the cats.:unamused: im severely tempted to ram a steel pipe through the cat and call it good.

Any thoughts gents?

[HeathyVT]

I think i'm going the test pipe or high flow cat route, these can be had for around 300 with a high flow cat,or 250 with a test pipe.

[bruceman]

I have a 95 Impreza 2.2 that had this code so I installed a spark plug non-fouler, that I picked up for $5 at Oreilly's, onto the rear O2 Sensor and bingo the next day the check engine light is no longer on:headbang:

Did nothing else, did not even disconnect battery to erase codes, just unplug the sensor, unscrew it, drill half inch hole in non-fouler plug, screwed O2 sensor into it and reinstalled in the car

[alosix]

How many miles does the car have on it? It's always possible it actually needs a new cat.

x2, painfully likely.

Though that showed up on my 02 WRX after swapping in a new bosch front 02 sensor.

Given that I'm currently a few cats short of a crazy old lady's house, I just plugged in the tactrix cable and lowered the threshold :).. Smog man seems good with the emissions :)

Jason

[A1337STI]

BTW, I'm running an 01 RS power train (in a 93) . I have the wide band front O2 sensor and a standard rear. I'm using a high flow cat from summit racing, think it was like $90 or something, Works perfect, my ecu is not tuned, and i do not get any warnings about cat efficiency.

If you do not race in a 'stock' class, might as well save a bunch of money and replace your factory cats with hi-flow racing models. :)

[gizzmo]

Have you priced O2 sensors?? The one after the cat is a "paltry" $60 or so. But I decided to see what it would cost me to replace the front one since I think it might be making me a touch rich. $215!!! I said "F-it" I'll have Thorne tune around it.

Get at me aboot that front o2. If you wanna stay factory I can hook you up for better then $215 I'm sure ;)

I think i'm going the test pipe or high flow cat route, these can be had for around 300 with a high flow cat,or 250 with a test pipe.

I have a cat pipe I'd let go that never threw any codes before I replaced it with a header w/ custom cat.

[Hites]

Get at me aboot that front o2. If you wanna stay factory I can hook you up for better then $215 I'm sure ;)


Fairly certain the problem has been resolved after two years.