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Old 10-16-2014, 02:10 PM   #1
luusir916
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How to check for which 02 sensor is bad?

Hi guys I only had this car for a little over a month and it was throwing the bad 02 sensor code. How do I check for which 02 sensor to replace? I tried searching everywhere for the topic but just could not find any thread regarding this issue, if anyone can link me or help me that would be awesome sauce! Thanks!
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Old 10-16-2014, 02:11 PM   #2
Mango
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A BMW-specific scanner will help you narrow down which sensor. As good practice, you should replace at least both pre-cat sensors
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Old 10-16-2014, 02:31 PM   #3
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A BMW specific tool is not required.

Any good generic OBDII scan tool is all that is required. Matter of fact a good generic OBDII tool can do a far better job flagging questionable O2 sensors than most manufacturer specific tools.

OBDII smart phone Apps and an interface are typically $30 or less.

See this thread with an example of how O2 sensors will never trigger any errors but still be bad and cause other problems - http://forum.e46fanatics.com/showthread.php?t=1041726

Also the only O2 sensor codes I usually run into that really indicate that an O2 sensor has a problem are O2 sensor heater failure codes. Any other O2 sensor code usually does not mean the O2 sensor is bad.

Need to see the specific codes and associated Freeze Frame data to be able to comment further.
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Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

Fuel pump failures - http://forum.e46fanatics.com/showthread.php?t=929501

Temp Info - http://forum.e46fanatics.com/showthread.php?t=964491

Hidden OBC Menu - Check Voltage, Temp, Fuel Level - http://forum.e46fanatics.com/showthread.php?t=239619

E46/E39 GM5 Door Lock Info - www.bmwgm5.com

Lower hose temp switch O-ring - BMW #13621743299
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Old 10-16-2014, 02:46 PM   #4
Mango
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Nobody said it was required, but it can tell you of many problems a generic scanner won't tell you, including ones related to fuel trim problems. Further, software like INPA can alert you to ghost codes and frequency of errors. This is helpful when you have a bunch of codes and reading them after clearing to see which codes pop up and how often, including shadow codes. It's a good idea in general to have good readers/software when diagnosing. Generic readers are better than nothing, but when you own a 10-year old German car, it's nice to have good stuff. Especially when it's cheap or free. GL, OP!
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Old 10-16-2014, 06:37 PM   #5
luusir916
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Thanks for the promptly responses. It started throwing a P0300 code soon after. Hoping when I change 02 sensors it will stop misfiring.
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Old 10-16-2014, 06:42 PM   #6
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Changing an O2 sensor(s) will not likely resolve your misfiring.

Need to focus on the misfiring and Fuel Trims.

Read the first 2 links below in my signature.
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Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

Fuel pump failures - http://forum.e46fanatics.com/showthread.php?t=929501

Temp Info - http://forum.e46fanatics.com/showthread.php?t=964491

Hidden OBC Menu - Check Voltage, Temp, Fuel Level - http://forum.e46fanatics.com/showthread.php?t=239619

E46/E39 GM5 Door Lock Info - www.bmwgm5.com

Lower hose temp switch O-ring - BMW #13621743299
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