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View Full Version : CEL: P0420 Catalyst Efficiency


Khanhfucious
09-07-2007, 02:27 PM
2000 Legacy GT Limited 2.5L 4EAT 97500 miles.

P0420 Catalyst Efficiency Below Threshold (Bank 1)

It cane on while I was cruising on the highway..

What can I do? I dont wanna replace a cat..because that sounds expensive..
rougeben83
09-07-2007, 02:46 PM
Are you running the stock cats?

You can get the little spacer to move the 02 sensor out, that usually works on hi-flo cats/test pipe applications.
Khanhfucious
09-07-2007, 02:55 PM
Yup stock cats..
MR.MCSICK
09-07-2007, 03:42 PM
Most likely the rear O2 sensor after the cat. Go there first.
Wiscon_Mark
09-07-2007, 05:13 PM
Most likely the rear O2 sensor after the cat. Go there first.

Quite right. It's probably not your cat.
Huffer
09-07-2007, 05:34 PM
I dunno, cats usually die after 90,000miles.

I would take the opportunity now to go with a hi-flow cat and install a rear O2 sensor spacer. You can either buy the spacer from Rallitek, or make your own with a drill and 2 HELP! brand spark plug anti-foulers.
Wiscon_Mark
09-07-2007, 06:10 PM
I dunno, cats usually die after 90,000miles.

Where do you get that idea?

Mine lasted 170,000 miles, and it was just the piping that rusted out, not the cats that went bad.
Reason
09-07-2007, 06:18 PM
Mine went bad a little over 70k.
Huffer
09-07-2007, 06:23 PM
I dunno, cats usually die after 90,000miles.

Where do you get that idea?

Mine lasted 170,000 miles, and it was just the piping that rusted out, not the cats that went bad.

EPA documentation...and mine rusted out at 180k, along with both sensors failing at that point.
Cats can fail for a number of reasons - and their efficiency diminishes each revolution of exhaust...
rougeben83
09-07-2007, 10:03 PM
Also, forgot to add I'd check the o2 sensor first (that code is for the rear) see if that's the problem.

Usually it's that vs. the actual cat.
Khanhfucious
09-08-2007, 08:46 AM
What do I check it for?

In my position, I dont want to spend ANY money on this car, because Im waiting for the 08 STi. I dont wanna go and spend $200 on 02 Sensors, and sell the car in 3 weeks.
Reason
09-08-2007, 09:09 AM
Buy some universal O2 sensors then. They are around $40 at a parts store.
Wiscon_Mark
09-08-2007, 09:51 AM
You only have to replace one of the o2 sensors - if the first one was having problems, your car would be running like crap. It's likely only the second o2 sensor that's out.
Huffer
09-08-2007, 10:21 AM
Federated Auto Parts carrys the OEM replacement for around $60-70. It's got the plug on the end so it's true plug and play.
Khanhfucious
09-08-2007, 01:04 PM
You only have to replace one of the o2 sensors - if the first one was having problems, your car would be running like crap. It's likely only the second o2 sensor that's out.
The CEL for the first one comes and goes. All this adds up to me wanting a new car. :grin:


I disconnected the battery and it went away. :roll:
ivwarrior
09-08-2007, 02:06 PM
It'll probably come back. Just remember to disconnect the battery again, right before you head to the dealership to trade it in. :grin:
Khanhfucious
09-08-2007, 02:34 PM
It'll probably come back. Just remember to disconnect the battery again, right before you head to the dealership to trade it in. :grin:
Thats what I plan on doing..Ill reset it every time it comes on (after I get it pulled to make sure thats it, that is)

I already know I WILL not sell my car to anyone other than a dealer. Lemon Law will take every bit of "advantage" I make by selling to private party.