Catalytic converter or O2 sensor - code 520
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Elder User
Joined: Jul 2001
Posts: 510
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From: Portland, OR
Catalytic converter or O2 sensor - code 520
Hey all, long time no post on this board. I have a 96 Bronco w/ 5.0 & 5-speed. It is posting a 420 - catalytic system efficiency below threshold". Took it to a muffler shop, basically they said it could be an O2 sensor fault (the one just behind the 1st cat). He poked around the converter, said it was full. They gave me a quote of $280 on a converter which I thought wasn't bad but I'm willing to risk the O2 sensor, especailly as I don't want to pay for the converter if that's not the problem.
Anyone have any experience here?
Thanks,
Biederboat
Anyone have any experience here?
Thanks,
Biederboat
Lead Driver
Joined: Sep 2002
Posts: 9,182
Likes: 12
From: Gateway to the West
Well, the shop certainly would rather sell you a new cat as well as the O2 sensor. And the answer is NOT that it "could be an O2 sensor fault"! The answer is YES, it IS an O2 sensor fault. Codes are not "maybe's" or "could be's". They are facts based upon computations made by the PCM. Since the whole system is not throwing an efficiency issue code, one would tend to think that particular bank of cylinders is either experiencing combustion efficiency issues OR the O2 sensor has gone the way of the Do-do. Since its highly suspicious that an entire half of the engine would have a problem and you would not feel the problem in the performance, the likelihood of the sensor going bad is looking more and more probable.
Elder User
Joined: Feb 2007
Posts: 601
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From: Chicagoland
Hey all, long time no post on this board. I have a 96 Bronco w/ 5.0 & 5-speed. It is posting a 420 - catalytic system efficiency below threshold". Took it to a muffler shop, basically they said it could be an O2 sensor fault (the one just behind the 1st cat). He poked around the converter, said it was full. They gave me a quote of $280 on a converter which I thought wasn't bad but I'm willing to risk the O2 sensor, especailly as I don't want to pay for the converter if that's not the problem.
Anyone have any experience here?
Thanks,
Biederboat
Anyone have any experience here?
Thanks,
Biederboat
Thread Starter
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Elder User
Joined: Jul 2001
Posts: 510
Likes: 0
From: Portland, OR
Well I took it to another shop that had a more sophisticated tester than mine, they checked the O2 sensor function and said it was fine. They replaced the cat and it passed just fine, no more codes. FYI, the "bank 1" is kind of misleading, it's the downstream sensor of the 1st cat so it's measuring the function of the 1st cat, not directly out of a cylinder bank.
Biederboat
Biederboat
