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General E46 Forum
This is the place to get answers, opinions and everything you need related to your E46 (sedan, coupe, convertible and wagon) BMW!

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Old 07-16-2017, 11:18 PM   #21
jfoj
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No there is a bigger problem here. You may have traced something wrong , there is some confusion or someone has installed sensors in the wrong location.

Here is the F**KED up problem, the engine bay harness is not labeled or if it is, it is not clear and very hard to find. The engine bay harness will have both Pre-cat sensors with the same style connector. Then both Post-cat sensors will have a different style connector. But each Pre or Post cat sensor should be able to be swapped between the 2 engine bay harnesses for the Pre or Post connection.

The Pre and Post cat sensor connectors differ, however, the Bank 1 & Band 2 connector are the same for reach sensor type. So Pre-cat sensor have the SAME style of connector while the Post-cat sensors have a different connector but the Post-cat sensor connectors are the same. If you understand what I am saying.

There should be NO wire cutting going on here.

This entire thing is STUPID easy, but is is so STUPID easy to get is all screwed up to Sunday. It is really not that hard, is just sucks trying to explain in without decent pictures and being hands on to the car. I can sort this crap out in 5 minutes with my eyes closed.

Either someone has swapped a Pre and Post cat O2 sensor in the exhaust, usually a bit tricky due to wiring harness length.

If this is all to confusing, buy 2 Bosch replacement Pre-cat O2 sensors and then install these ONLY in the front O2 sensor slots. You will then still need to get the proper banks sorted out, but you may find in the process something is totally screwed up.

I suspect this is a problem car based on the mileage listed with the SES/CEL/MIL on and the current codes.

Someone did something stupid here a long time ago with this car is my guess.
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Old 07-17-2017, 08:34 AM   #22
tomandhisjones
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So, I found this image to try and show what the connectors look like for both pre cat sensors.



They are different plug types. It makes me wonder if at some point, the o2 sensors got put into the wrong spot on the headers, and someone rewired them.
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Old 07-17-2017, 09:14 AM   #23
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So, for more context, when I first got this car and was trying to figure out what was going on, I took it to a local indy shop that said my cats were aftermarket. I don't have any record of when this was done. It makes me wonder if when the cats were put in, if they hooked up the o2s wrong, and then my local shop just replaced the o2s in the spots that the old ones had already been in, instead of looking at a diagram on where they should go.
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Old 07-17-2017, 09:33 AM   #24
jfoj
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OK, I do not deal with as many M3 problems, the non M cars have the same Pre-cat O2 sensor part number for both banks.

It does look like the M3 had a different part number for the Pre-cat O2 sensors for each bank. Not sure if this is just a wiring harness length difference and/or the connector is different.

It does appear from that the Post-cat O2 sensor also have a different part number, so they may not be able to be swapped Bank to Bank if the connector is different. Sometimes the O2 sensor part number is different just due to the length of the wiring and some of them have different color outer jackets to help identify the correct location.

So if the Pre-cat O2 sensors have different connectors, then it is IMPORTANT the correct O2 sensor gets put in the proper Bank location!!! Also if the car has aftermarket headers, often the O2 sensor locations are not the same as stock and the wiring length may be too short.

I do not want to have you chasing your tail, but you need to be 10000000% sure you have the labeling correct and the Logs correct, because I am only as good as the information provided to me.

In short, if everything you have provide is correct and you cannot swap the O2 sensor connections Bank to Bank due to a keyed connector, then the O2 sensors were installed in the wrong header/exhaust manifold!! I do not think anything was rewired unless you can find evidence of wire splicing or repair. It may be as simple as the sensors being installed in the wrong locations.

Go figure, but this is not the first, nor the last time this will happen and it will totally cause the engine to run like crap.

See the Bosch Auto Parts web site for more info. You MUST add your vehicle to the Trim level for the site to narrow down the part numbers. Unfortunately Bosch does not see the need for good pictures with close ups and details on hte wiring length. You might also check ESC Tunings web site once you have the correct part numbers as they may have good close ups on the O2 sensor connectors.
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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

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Lower hose temp switch O-ring - BMW #13621743299

Last edited by jfoj; 07-17-2017 at 09:35 AM.
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Old 07-17-2017, 10:00 AM   #25
tomandhisjones
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Yeah, I believe all four sensors have different plugs / lengths, which is why there are four part numbers. I have 99% confidence in the data that I sent you. I'm with you on thinking that the sensors are installed in the wrong ports. I'm going to crawl under the car, and try to trace everything tonight.
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Old 07-17-2017, 11:22 AM   #26
jfoj
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Keep in mind, if the exhaust manifolds/headers are not original, the O2 bungs may be too far down and the stock O2 sensor leads may still be too short.

You need to be careful about how you address O2 sensor wiring that is not long enough. O2 sensor signals are polarity specific.
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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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