P0492, Cylinder head blockage???

[Old525i]

Got a P0492 OBD code: insufficient air flow into bank 2. My car is a 2008, 328i with the N51 6 cylinder, 24 valve engine (SULEV)
Air pump, valve, hose and relay all check out good.
When the air valve is out of the engine, bank one flows air from an air hose at 100 psi easily.
Bank 2 (cylinders 4, 5 and 6) seem blocked since there is no air flow at all.

Thoughts? I won't be able to renew registration unless there are no OBD codes present.

One mechanic told me I needed a new engine. Another said that the cylinder head needs to come off.

[JDStrickland]

Me thinks you need to pull the intake manifold and look for blockage, rodents come to mind. Maybe you could just remove the throttle body and peer into the intake manifold, but I would not expect an engine change.

You have the N51, it makes sense that you find out if there is warranty coverage for this. The N51 gets expanded warranty coverage for engine management kinds of things.

[Old525i]

I think the warranty expired on SULEV cars. This car has 296,000 miles. The air pump blows air over the exhaust side, not the intake side. Thanks for your comments.

[Old525i]

Fixed it!

Bought an old secondary air valve off eBay, removed the top and used the bottom to pour B12 Chemtool liquid. I created a metal gasket to block the liquid from going into the front side of the engine since that side always had good flow and no OBDII codes. Since the rear passages were fully blocked, I just filled the valve with B12 juice and kept it filled for a few days, occasionally pushing the liquid with a 100 PSI air-hose. After a few days and the blockage still present, reassembled the original valve and hose and tried to start the car. It took two days of repeated attempts to start until eventually some liquid came off the tailpipe and started. Took it for a fast run on the freeway and eventually the computer cleared the permanent code that had been set over the last two years.

[davek917]

@Old525i I think this is exactly the issue I am having. Local mechanics and dealer are trying to tell me that this is going to be a huge job to fix for emissions. Would you be able to post some photos of what you did?

[Old525i]

@Old525i I think this is exactly the issue I am having. Local mechanics and dealer are trying to tell me that this is going to be a huge job to fix for emissions. Would you be able to post some photos of what you did?

Dave: I fixed it about a year ago and I am sorry to say I didn't take any pictures. After the permanent code went away, I took it to the smog station and was able to renew the registration for two more years. Then, two weeks later, the dreaded "catalytic converter below efficiency" showed up for both cats. I tried to use a spacer to move the O2 sensors back, but that didn't help. So starting March 2024, I won't be able to register the car in California anymore. By then, the engine will be up to 315,000 so I think it is time to get a new car. The engine is still very strong, that is not enough to convince the bureaucrats in California. PS: I will never buy a BMW again. They have gotten too complicated to take someone from point A to B.

[dfyoung10]

Hi, I don't know if this will reach you after two years, but here's hoping. 2010 328i E90 SULEV <90,000 miles, just now out of SULEV coverage. Like you, I have the same P0492 (Bank 2) code coming up, and while I am not facing smog renewal issues for more than a year, I am trying to stay ahead of it. This came up two years ago and the dealer fixed it, though not without some SULEV extended warranty drama. While I was tracking down a misfire issue, I noticed the P0492 code again, though no CEL yet. I deduced that P0492 without P0491 (Bank 1) almost has to be blockage in the rear bank, because all equipment is shared by both Bank 1 and Bank 2 until the path splits below the air valve at the exhaust manifold.

A couple questions: 1) How did you determine that the rear bank was blocked? Was it visible? 2) Did you try mechanically removing the blockage, i.e., with a drill, brush etc.? 3) Do you think some of the crap you cleared out ended up in the Cat, causing the subsequent issue?

Any thoughts would be welcome.

Thanks, Doug