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E36 (1991 - 1999)
The E36 chassis 3-Series BMW was a huge hit among driving enthusiasts from the first moment the car hit the pavement. The E36 won numerous awards over the years it was produced and is still a favorite of many BMW enthusiasts to this day! -- View the E36 Wiki

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  #1  
Old 05-03-2013, 09:42 AM
BIGAAUTOS BIGAAUTOS is offline
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e36 323i convertible P0155 Check Engine Light on changed oxygen sensors, what next?

I have a 1998 323i convertible. I recently changed the engine computer. The car keeps throwing a p0155 code. So I changed out all 2 of the o2 sensors, there are only 2 in this one, the upper ones by the manifold are plugged.

Deleted the code and the check engine light came back on immediately. The same p0155 code. So I swapped it for another o2 sensor. Deleted the code, came back immediately.

I traced the wire, everything is perfect all the way to the harness that goes to the Engine computer. I also replaced the o2 heater relay, which had no effect. Then I swapped it with another of the same relays in the fuse box to make sure that the relay is good. Still did not fix the problem.

The light immediately comes on every time it is cleared. If I clear the code and with the engine OFF, the light stays OFF,,,, once the car is started, the check engine light immediately comes ON. Any suggestions on something to check or double check? ALL suggestions or thoughts are appreciated!!! Mike

Last edited by BIGAAUTOS; 05-03-2013 at 09:44 AM.
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Old 05-03-2013, 11:01 AM
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hornhospital hornhospital is offline
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Might be the fact that someone deleted the pre-cat O2 sensors.
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Old 05-03-2013, 11:25 AM
BIGAAUTOS BIGAAUTOS is offline
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Quote:
Originally Posted by hornhospital View Post
Might be the fact that someone deleted the pre-cat O2 sensors.
Oh! I replaced the engine computer with an engine computer from a 328i, which HAS the pre cat o2 sensors. The 323i does not have these. This is the reason for the check engine light! I need to replace it with a 323i computer. I will post back to confirm the fix after I find the computers.
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Old 05-03-2013, 11:37 AM
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hornhospital hornhospital is offline
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Uh, ALL OBD2 BMWs have pre-cat O2 sensors, and the 323i is OBD2.
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Old 05-03-2013, 12:49 PM
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dc_wright dc_wright is offline
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It's interesting Ken, I was going to blow back that same answer earlier, but out of curiosity I looked on BMW fans and it shows the US 323 Cabrio set up actually has the two ports in the exhaust manifold plugged and a single pre-cat O2. Go figure.....
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Old 05-03-2013, 02:00 PM
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that's because the 323 runs a similar exhaut to the obd1 setup with a 'y' connector, iirc, and why swapping in an obd2 exhaust midpipe from a 328 or //M is a huge benefit.

why they did it like that, though, i cannot say. makes no sense to me, especially if they had to close off the ports on the exhaust manifolds to do so...




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Old 05-03-2013, 04:20 PM
BIGAAUTOS BIGAAUTOS is offline
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Swapped out the engine computers and it fixed the problem.
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Old 05-03-2013, 04:24 PM
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hornhospital hornhospital is offline
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Re: e36 323i convertible P0155 Check Engine Light on changed oxygen sensors, what nex

Bizarre! But it's still should have a pre-cat O2 sensor, correct? The OP said he replaced two O2 sensors and if I read it correctly they are post-cat. Since the post-cat sensors don't actually regulate anything like the pre-cat sensor(s) do, how's the ECU getting mixture regulation information?

Edit: glad you got it sorted!
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1995 318is "Bebe"; 1993 325is "Elvira" 1985 635CSi "Katja" 1984 633CSi "Sylvia"
HAVE I HAD MY MEDS YET?


Last edited by hornhospital; 05-03-2013 at 04:26 PM.
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