Failed emission test for P0491.

[BimmerRob08]

Hey fella's,

So yesterday my '08 E92 M3 failed emissions for code P0491. My M3 is fitted with encore high-flow CAT's and DINAN Software Stage II. I moved to Nevada and used to live in New Mexico where my M3 would pass just fine with DINAN stage II and high flow CAT's. Never through this code before. Only has 78,000 miles and well taken care of. I have not yet gotten BMW here to diagnose it and looking to find answers first before I waste money at a dealership and get a run-around as I'm new to this area. One issue now is the BMW dealers in Las Vegas dropped DINAN and so I'm at a loss of who would be able to redownload it after working on the M3. Normally I had BMW handle it all but now that is going to be an issue I'm guessing.

My google search for this code for the E92 doesn't bring up much from others experiencing the code but points to a oxygen pump. What are your thoughts on this? Search brings up the fallowing from another posting. Most likely I can replace them easily but chasing a vacuum leak as we know can be a real pain in the ass. Any constructive suggestions are appreciated. Thanks!

1) Air pump failure
2) Check valve failure
3) Vacuum line failure
4) Vacuum pump failure

[BimmerRob08]

hello? Anyone? Help please!

[BayE30]

those are probably coded out as part of the stg2 tune. will have to get your OE tune loaded back into the car, and the stock midpipe as well to set monitors and pass smog.

[Stainless 45]

Definitely sounds like you have a vacuum leak. Look for any separated or broken hoses. Any CEL will usually cause you to fail inspection

[dpaul]

That's a secondary air pump code. Either the pump is bad or the check valves are bad or there is a leak in one of the hoses. If there is a significant leak, you'll hear the hiss - usually not subtle.

The fact that you are seeing only P0491 (bank 1) and not both P0491 and P0492 (bank 2) may suggest that the problem is either bank 1 check valve or a bank 1 related hose, rather than the pump itself

[BimmerRob08]

Originally Posted by dpaul

That's a secondary air pump code. Either the pump is bad or the check valves are bad or there is a leak in one of the hoses. If there is a significant leak, you'll hear the hiss - usually not subtle.

The fact that you are seeing only P0491 (bank 1) and not both P0491 and P0492 (bank 2) may suggest that the problem is either bank 1 check valve or a bank 1 related hose, rather than the pump itself

Thanks man. Glad you got some smarts on this subject. I'll start with your flow. Much appreciated. In the past with my DINAN stage II software, the encore innovations HFC I have, I've never failed a smog test out west (NM where I had the local BMW dealer install the software). I report back with findings when I can start working on it.

[scaryharry19]

Originally Posted by BimmerRob08

Thanks man. Glad you got some smarts on this subject. I'll start with your flow. Much appreciated. In the past with my DINAN stage II software, the encore innovations HFC I have, I've never failed a smog test out west (NM where I had the local BMW dealer install the software). I report back with findings when I can start working on it.

Sorry to come in a year later.. you ever figure this out? I've got the same code along with 00274A, 00279D, 002743

[BimmerRob08]

Originally Posted by scaryharry19

Sorry to come in a year later.. you ever figure this out? I've got the same code along with 00274A, 00279D, 002743

So what is was, was the pre-CAT O2 sensor on I think was back 1. My local BMW private tuner shop diagnosed it so I put a new O2 sensor. Now days I live in a non emissions town so I’ve not gotten it smog tested in a long time. Still running HFC and stage II. Other probably fake one of I had to get it done.