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E36 M3 (1995-1999)

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Old 02-09-2009, 08:59 AM
NCM3 NCM3 is offline
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Location: North Carolina
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Mein Auto: 1998 M3
'98 m3 catalyst error code troubleshooting

I am using the Bavarian Autosport Fault code reader. My check engine light comes one and I check and get 2 errors:

Catalyst efficiency below threshold Cy #1-3
Catalyst efficiency below threshold Cy #4-6

I had a factory catalyst which apparently was broken inside (ceramic I guess?). I had a local shop replace the catalytic converter with a Bavarian autosport model (legal in all states but calfornia model). They replaced but would not warranty. The check engine kept coming on with this same message. I ordered some Bosche oxygen sensors and had a local BMW mechanic replace them. The light still comes on from time to time.

Any ideas on what the problem might be?
'98 M3 Owner
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Old 02-11-2009, 04:05 AM
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rrsperry rrsperry is offline
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Location: Maryland
Join Date: Oct 2003
Posts: 485
Mein Auto: ///M3 sc
Your car has 4 O2 sensors, @ in the exhaust manifold and after the cat. The efficiency light is usually when the post cat sensors are out of spec with respect to the pre cat sensors.

What I would try to do is see if you can find an obd2 code reader that will allow you to monitor sensor and ecu outputs in real time. There are several pc based, and even some pda packages. Of fond someone with a GT1 and go from there.
No matter where you go, there you are.
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Old 02-11-2009, 09:08 PM
e30e e30e is offline
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Mein Auto: e36 m3/4
Did you replace all 4 o2 sensors?
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