# Check Engine Light Headache



## jlatorre (Jul 2, 2010)

Hi all,

Driving a 2000 Altima GLE. Back in '07 had the light come on. Dealership said I needed a new catalytic converter. Went to a local guy to replace the cat with an after market converter. Eventually the light turned off. Since then, it's been off and on over the years. It's turned off a few times this year, but not since I've needed to get it inspected!

The two codes Autozone gives me are for the catalytic converter and the knock sensor. Does anyone have experience with this? The guys at the dealership told me any non-Nissan cat is going to set off the code.

Should I look into replacing the O2 sensor? I've had that code in the past. This light does turn on and off on occasion. I don't want to replace the cat (expensive)

Let me know - I'm not the most knowledgable when it comes to this subject!

Thanks,
Jay


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## altimanum1 (Jun 19, 2009)

Do you know the code numbers? Knock sensor is a REALLY fix. If you replaced the catalyst conv. i doubt thats the problem. DID they install the O2 sensor that goes by the catalyst conv.?


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## jlatorre (Jul 2, 2010)

The two codes are PO325 Knock Sensor Circuit Malfunction Bank 1 / Sensor 1

and

PO420 Catalyst Efficiency Below Threshold Bank 1

I haven't had any O2 sensor replacements. I was leaning towards changing it. I'm not an expert but it looks like I have two sensors. Is this the right direction to go in? Any idea of which one is most likely to have gone bad?


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## bnorah (Jun 10, 2008)

Wow, I wish I would have seen this post before posting my new thread! I feel like an echo now.


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