2010 E90 328i SULEV, <90,000 miles. I was checking codes for a misfire issue recently and discovered code P0492, Insufficient Secondary Air supply, Bank 2 (cylinders 4-6). I had had this code a few years ago causing the car to fail California smog certification. It was under SULEV warranty then, and the dealer fixed it, though not without some SULEV drama over the $1200 bill. The car is no longer under the 15-year warranty, and though I am not facing smog check for some time, I wanted to try to get ahead of it.

On examination, I had a nice robust air flow out of the air pump, the hose looked good and the check valve passed the suck/blow test.

Notably, there was no code for P0491, (Bank one), meaning cylinders 1-3. Both “banks” share all the mechanical components, e.g., intake filter, pump, pump relay, hose and check valve, until the air flow splits into separate banks under the check valve on top of the exhaust manifold. Since there was no code showing for Bank 1, I decided the problem must be in the rear part of the exhaust manifold itself, since that is the only place the components are not shared.

So I took an old bicycle brake cable and cut the end off, intentionally mangling the cut end so I had a brushy tip. I ran the cable a few times in and out of the small passage into the interior of the manifold where the check valve mounts.

I then buttoned it all back up and cleared the existing code. It has been a couple weeks and the code hasn’t come back. Here’s hoping.