fault code: secondary air system

[sballard]

On my 1999 E36 328is, I had secondary air pump that started making a lot of noise about a year ago but no error codes ever showed. I replaced it along with the recommended valve ($$$$!) and guess what - the freaking "new" pump was still noisy! I just decided to live with it. Well, yesterday I got an error code for "Secondary air system flow too low, Cyl #4-6". I don't really know how to approach it. Has anyone experienced this and suggest how to fix it?

[Jeron]

With all codes I like to reset them and see if they reappear.

Cant say for sure but I would guess the message is triggered by the O2 sensors during the warmup phase. For the flow to be tool ow just to that bank there would have to be a blockage in the little manifold that runs from the air pump to the exhaust manifold. That seems unlikely but it shouldn't be too hard to check out.

If that checks out then I suspect it will be the early stages of an O2 or a cat problem.

[sballard]

Thanks, Jeron. I reset the codes and the message went away. It never occurred to me that it could be one of the oxygen sensors, but I'll bet you are right. The car has 110K on the clock and I've never changed the sensors. If it comes on again, I will just replace all of them.

Many thanks

[Jeron]

O2 sensors are expensive and I was just "guessing". I don't know if I would just replace them especially not all of them.