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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > o2 sensors are bad, how to indentify?



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      10-30-2012, 09:27 PM   #1
tmurphy2
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o2 sensors are bad, how to indentify?

i have one or multiple bad o2 sensors.

i was getting lean faults 29e0 and 29e1 and after checking every possible thing that could cause this we came up with nothing. THEN i got the following codes (below) which cobb says are bad pre cat o2 sensors. since these run 250 a pop how do i figure out for sure which ones are bad? BMW's test for these will show that they are good even if they are bad so thats not an option.

since there are 4 sensors total i dont want to just replace all of them because id be spending a $1000 to fix an issue that may only ba $250 issue... or a $500 issue.

anyone have any ideas of how to show which o2 sensor is bad?

these are my codes:

2caa
2c9c
2ca6
2cab
2c9d
2ca7
2c9c
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      10-31-2012, 04:32 AM   #2
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the code will always tell you if its bank 1 or 2. Search for the codes and their explanation. There are probably many threads related to them which will point you to the right direction.
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      10-31-2012, 07:31 AM   #3
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Quote:
Originally Posted by tmurphy2
BMW's test for these will show that they are good even if they are bad so thats not an option.

since there are 4 sensors total i dont want to just replace all of them because id be spending a $1000 to fix an issue that may only ba $250 issue... or a $500 issue.
Quoted for ignorance. You won't get much help calling out the pros when you're asking people you don't know for online help. Hell, spend the grand on them, just to find out it was an installation error. Being an exhaust leak, mixed up sensor locations, no/wrong dp fix, etc.
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      10-31-2012, 05:20 PM   #4
tmurphy2
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Quote:
Originally Posted by Bmw135er View Post
Quoted for ignorance. You won't get much help calling out the pros when you're asking people you don't know for online help. Hell, spend the grand on them, just to find out it was an installation error. Being an exhaust leak, mixed up sensor locations, no/wrong dp fix, etc.
what did i say that was ignorant and what pro am i calling out? we checked all those issues and more that you listed to rule them out, i was with my tech at BMW for 3 hours in the bay as we went through everything. now that I know its bad o2 im asking how do you identify which one it is.....not getting what the issue is.
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      10-31-2012, 05:22 PM   #5
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Quote:
Originally Posted by enrita View Post
the code will always tell you if its bank 1 or 2. Search for the codes and their explanation. There are probably many threads related to them which will point you to the right direction.
its bank one an two, i did a search and saw peoples posts about these codes...the thing is i know what the codes are saying i just dont know which sensors they are from.
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      10-31-2012, 05:26 PM   #6
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you can probably tell by logging for WBs... I have a slow one which is very obvious. wouldn't consider it bad yet though and no codes.
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      10-31-2012, 09:47 PM   #7
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Bosch 17098 can be used in both banks pre cat. Cost about $110 each.

But for that many codes for both sensors, did anyone check the fuse for the O2 heaters? Wiring problem? Check the heater circuits for continuity? Did anyone hit the O2 sensors or hit the exhaust to dislodge a broken stud?
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      10-31-2012, 09:56 PM   #8
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Quote:
Originally Posted by tmurphy2 View Post
i was with my tech at BMW for 3 hours in the bay as we went through everything. now that I know its bad o2 im asking how do you identify which one it is...
And not to be a dick, but 3 hours spent diagnosing to not even know which sensors to replace? These problems take 30-45 mins to check, start to finish, to determine whether you have a bad fuse, bad wiring, bad ground, or bad component. The code verbiage, which any mechanic worth his salt will have, tells you exactly which bank and pre or post cat. Most of those codes are the same for all modern BMW ECUs, too.
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      10-31-2012, 10:03 PM   #9
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Quote:
Originally Posted by JamesM3M5 View Post
And not to be a dick, but 3 hours spent diagnosing to not even know which sensors to replace? These problems take 30-45 mins to check, start to finish, to determine whether you have a bad fuse, bad wiring, bad ground, or bad component. The code verbiage, which any mechanic worth his salt will have, tells you exactly which bank and pre or post cat. Most of those codes are the same for all modern BMW ECUs, too.
if you read my orgianal post it said i had lean faults, just two codes one for each bank, i did not have an o2 sensor codes. quote "THEN" i got a bunch of o2 sensor codes. if had those codes when i was at BMW then you are right it wouldnt have taken 3 hours, but a lean fault can be caused by a lot of things and we didnt at the time think o2 because there were no o2 faults.

regardless thanks
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      10-31-2012, 10:46 PM   #10
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How did you go from lean codes, taking 3 hours to check what you could have verified in about 30 minutes of logging and checking with the AP, to having a slew of pre-cat O2 sensor codes - heater circuit, temperature, etc? Posting a list of codes before doing a simple google search is a little foolish, since there are posts all over that state the code verbiage for those you posted.

If you search first, post with more information and details, then ask questions, this thread would be clearer. I don't understand how you skip from lean codes to suddenly having a bunch of codes that you don't know what to do with other than, "I have one or more bad O2 sensors."

Did anyone mess with the pre-cat sensors? Accidentally pop the O2 heater fuse? Leave something unplugged? Whenever a customer comes to me asking or telling me to replace a part, my due diligence is to not do the requested work blindly, but to ask WHY. What are the steps they took to determine the reason? If their diagnostics are sound, I will still do the same diagnostics to ensure they're not wasting their money or my time. This has saved a lot of everyone's time and money.
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      11-01-2012, 11:03 AM   #11
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Mine has an occasional bank 1 primary and bank 2 secondary cat lean codes. I too would love too know a good way to test them. My car runs great, which makes me think I just need to play with the O2 modifier on the procede.

x...
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