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I needed some help if someone had a similar problem. My m5 is due for a smog test an i went today to a test only center after plugging in to his obd2 computer the state scanner notifys smog station that engine light is on. Although my display doesn't show a engine light. Also during initial engine start i dont get a engine block to be displayed an shut off it never crossed my mind. The smog station computer said catalyst system low level efficiency he cleared the engine light an told me to drive car so it can be smogged the following day after 40 miles. Well i was wondering if anyone can give me any pointers if it might be my aftermarket stereo equipment, afe intake, headers, muffler? I do have stock cats! Any help is appreciated. Thanks
 

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First of all, the shop is pretty helpful for just clearing the trouble codes and let you drive to see if the codes don't return then they'll pass your car. Secondly the light, if it doesn't come on when you turn the ignition on and then go off, then either the light was taken out by someone intentionally or it just blew out.
Cat efficiency below threshold could be due to a few reasons but most likely could be from the headers or the mufflers. Chances are that it could only be the upstream 02 sensors on whichever bank is lacking efficiency or the Cat itself. Drive it for that cycle that you were told if the codes don't reappear on obd then you'll be good to go. Still you can always check it a few hundred miles after they might reappear later on. Then at that time you could take care of them.
GL
 
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Just want to point something out. You don't have stock cats...you have NO cats. In your signature it shows you have the Evosport headers which totally remove the primary cats. You have cat inefficiency warning because you are lacking the primary cats which are in the stock headers which provide burn down of the fuel in the exhaust. Hence, the secondary O2 sensors (the ones which test for cat efficiency as it relates to fuel burn off) are sensing a higher level of fuel in the exhaust.

Most aftermarket software simply removes the CEL from displaying on the dash. It will not stop the condition from actual being present, nor stop the detection of the codes.

Here is how I have handled it on my E60 M5's with a similar setup:

Extend the secondary O2 sensors to just behind the secondary cats. Your shop will need to install an O2 "bung" hole for this. After that, as long as it was properly placed near the cat, you should pass. I have every year with that same setup and header package on my previous 2006 M5.

Hope this helps.

Darren
 
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