Catalytic Converter efficiency?

2001 BMW 525I
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DAVEGLASS
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I am getting four error codes from my scanner:

1. Catalytic Converter efficiency, Cyl 1-3
2. Oxygen Sensor Control Limit, Cyl 1-3
3. Oxygen Sensor ADaption Limit, Cyl 1-3
4. Oxygen Sensor Adaption Limit, Cyl 4-6.

I have read several forums in which I should look at my MAF sensor or vacuum leak or possibly the gas cap. Have you heard of such a problem with multiple problems showing up at one time.

I have replaced the O2 sensors, cleaned the MAF with cleaner from Autozone and still have the same 'Service Engine' problem.

Any suggestions.....
Dec 13, 2008 at 7:32 PM
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KASEKENNY
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More than likely you have a failing converter. However, we can run through some testing to confirm this. Here are guides that will help with all this:

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

https://www.2carpros.com/articles/catalytic-converter-replacement

https://www.2carpros.com/articles/how-to-test-an-oxygen-sensor-02-sensor

More then likely this is not a MAF sensor because basically these codes are telling you that the sensors are seeing out side the limit of where they are set. That is normally a sensor issue but since you replaced the sensors, I suspect the converters have failed.

I attached the process from the manual below on how to replace these if this proves out.

Please run through this material and let us know if you have questions. Thanks
Aug 25, 2021 at 7:06 PM