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Discussion Starter · #1 ·
hello, I would appreciate any suggestions. Bought my first e46 month ago. Week ago I have replaced the cat plus upstream and downstream o2s cuz the car was straight piped. After a day or two after replacing these parts cel popped up with this code. Checked both o2s via obd scanner. They are doing what theyre supposed to do when the car is cold (at least i think so). Once the car gets to operating temp the downstream o2 starts mirroring the upstream one. Could it be because of some kind of tune? When it was straightpiped, downstream o2 was disconnected and no cel ever appeared. Or is it maybe because of non oem cat?
2001 316i M43B19 1.9L
 

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Post-cat O2 behavior like the pre-cat one means the cat is not working.
It could also mean a pre-cat sensor is plugged into a post-cat sensor plug.
Verify all connections are correct.
 

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With the 4 cylinder engines theres only one post and pre cat, no chance anything could be mixed up here.

Post cat following pre cat shows the cat isnt working. I’m going with bad aftermarket cat, I cant think of any other reason the post cat sensor would be switching like the precat
 

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Discussion Starter · #4 ·
Is there any chance that leak in exhaust manifold would cause this code to trip? Or maybe something else that would cause the engine to run rich? I suppose there would be other codes instead of only that p0420. Also my obd shows that cat readiness is ready. But o2 sensor, o2 sensor heater and secondary air system are not. Eventho Im not sure if that has to do anything about it. Other problem about the car is that when its alreay warmed up and i turn the engine on, rpm drop to 500ish about three times, car start to shake like its about to stall and after like 10 sec it gets back to normal. When the car is cold and i crank the car on, it does not behave like this.
 

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Discussion Starter · #9 ·
So my guess the code is set because of rotten vacuum lines from air check valve. Hoses from there are connected to the fuel pressure regulator and to the intake manifold. Even the air check valve is connected to the exhaust manifold via metal pipe. That would cause wrong fuel pressure, extra air entering intake manifold and maybe even extra air in exhaust manifold/leak from manifold. Ill see if that will solve my problem. Even if it doesnt they need to be replaced :D
 

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Discussion Starter · #12 ·
So another update and last post on this thread. Loose plugs werent root of this code. Tried plug non fouler on the downstream o2. Didnt solve the problem. I have disconnected the rear o2, checked obd scanner. Car acts like theres still that rear sensor connected. Voltage is steady and dead on 0.47 V. So that fokin car is tuned as i thought in the beginning. Also explains why there were no codes when the car was straight piped with disconnected rear o2. x) Im dead
 
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