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E36 M3 (1992-1999) {Euro - S50 B32 321hp @ 7400 rpm} {U.S. - S52 B32 240 hp @ 6000 rpm}
Total Produced: 71,212 - Years Produced: 1992 to 1999


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Old Mon, Oct-30-2017, 07:41:17 PM   #1
migrabis
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Default P0136 and P0141 Codes

Hello everyone, this is my first post. I have a 97 M3 that I recently installed Raceland long tube headers on and I welded a custom catless midpipe for it. The car pulls hard and I am very happy with the upgrade, other than the headache from the CEL.

The CEL is for P0136 and P0141 codes and I cannot seem to diagnose it. I already swapped out the bank 1, post cat O2 sensor, thinking that would clear the code. Since the CEL still showed up, I tried swapping the connections between the bank 1 and bank 2 post cat sensors and interestingly enough the code didn't change from bank 1 to bank 2, so therefore I am lead to believe that this issue is with the upstream wiring or something else, not the O2 sensors themselves. Not sure if this matters, but I didn't completely delete the SAP - I simply left it in the engine bay without plugging it into the new headers since there are no holes for it.

Does anyone have any input on this situation/what I can try?

Edit: I also machined/welded 90 degree "elbow" spacers for the O2 sensors. Since I don't have CATs I wanted to space those out from the hot gases.

Last edited by migrabis; Mon, Oct-30-2017 at 07:45:35 PM.
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Old Mon, Oct-30-2017, 08:29:47 PM   #2
migrabis
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Default Re: P0136 and P0141 Codes

Quote:
Originally Posted by Braymond141 View Post
You really think uninstalled post cat O2 sensors would go unnoticed by the ECU?! Get a tune for this so you can properly delete it (I have an ECU with EWS delete/SAP/Rear O2 plus mild tune if you’re interested).
I understand that removal of the post cat O2 sensors will trigger a CEL and thatis why I have both of them installed into both of the midpipes they are just spaced out. If they were uninstalled I would surely be throwing codes in both banks 1 and 2. My hope is to still be able to pass emissions (Illinois just requires OBDII readiness).
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Old Mon, Oct-30-2017, 09:00:02 PM   #3
Braymond141
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Default Re: P0136 and P0141 Codes

Nevermind. I read that all wrong.
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Old Mon, Oct-30-2017, 09:17:22 PM   #4
tsmith25
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Default Re: P0136 and P0141 Codes

It sounds like they are not getting hot enough because of the spacers.
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Old Mon, Oct-30-2017, 09:21:07 PM   #5
migrabis
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Default Re: P0136 and P0141 Codes

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Originally Posted by tsmith25 View Post
It sounds like they are not getting hot enough because of the spacers.
That's what I was considering as well, but the CEL pops up within a second or two of me starting the car. Would that be enough time for the ECU to register the o2 sensor is not being heated properly? The spacers are exactly the same dimensions-wise so it would be weird that 1 of them is fine and the other is throwing codes.
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Old Tue, Oct-31-2017, 05:44:40 AM   #6
migrabis
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Default Re: P0136 and P0141 Codes

Just another update to this situation.

I checked all 4 o2 sensor voltages using the Torque app and drove around to make sure the numbers were accurate. Bank 1 and 2 pre-cat sensors as well as bank 2 post-cat sensor all read 1V when I was driving and then fluctuated to lower numbers while idling.
I then swapped the post-cat o2 sensor connections between bank 1 and bank 2 to check the voltages - I cleared the code, drove around again, and nothing changed so this reaffirms it is not a sensor issue.

I will pull my DME tomorrow and check if there are any damaged pins, I found a similar issue someone had with their E46. If all the pins are intact, I will try to find melted wires or something of that nature which could have been damaged. The o2 sensor that I previously replaced had some exposed wiring from hitting the heat shield above the midpipe and that might have caused a short or some wiring to get damaged.
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Discussing P0136 and P0141 Codes in the E36 M3 (1992-1999) Forum - {Euro - S50 B32 321hp @ 7400 rpm} {U.S. - S52 B32 240 hp @ 6000 rpm}
Total Produced: 71,212 - Years Produced: 1992 to 1999 at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)