diagnosing secondary air pump failure on 98' 528i

It might be working correctly. The air pump is supposed to turn on during a cold start and just run for a little while. It then turns itself off.

Usually, if they fail the "Check Engine" (or whatever its labelled) will turn itself on and set a code.

If it is really noisy, I guess the bearings might be starting to go on the air pump.

I wouldn't pay too much attention to the codes. Just locate the pump, and verify that the racket is coming from it (obviously you'll need to open the hood to do this; just check it at idle just after the cold start). What you've described sounds a lot like this is indeed your problem.

The car should run without it, but you should replace if it's crapped out on you.

Yes, you should easily be able to replace the thing--very easy job, but the pump itself will set you back $200-300 I think.

----- Kill ratio of Palestinian children to Israeli children 5.7-to-1, Israel's favor. Kill ratio of all Palestinians to Israelis: over 3-to-1.

---------

"Don't worry about American pressure on Israel. We, the Jewish people, control America, and the Americans know it." ---Israeli Prime Minister Ariel Sharon, 2001

It might be worth paying someone to check the codes rather than flailing and throwing parts at the car. The secondary air pump is not effected at all by turning the wheels. The noise you hear might well be your power steering pump.

See above - although a power steering pump won't throw a failure code. Is your Check Engine Soon light on?

The secondary air pump only runs for about 15 seconds when the temperature is below a certain temp (I believe around 50F) and the engine temp is cold. It injects additional air into the exhaust stream to help fire off the catalytic converters. It not working will have absolutely no effect on your car's performance, and will not injure it at all. It will cause you to fail inspection if you're in the US and in a state that checks emission codes via the OBD-II port.

Depends on your skill level. If you regularly stab yourself when handed screwdrivers - I'd go to the dealer or a good independent mechanic. If you can change a tire - you can probably change this pump. While changing it - you should also change the valve that is supposed to prevent backflow from the exhaust into the pump. This valve failing is typically what causes the pump to go south.

It's PN#3 in the drawing.

No problem.

It definately is more severe when I turn the wheel, even though it only lasts around 5 minutes. Would a failing power steering pump exhibit such behavior?

Yep. I think we just ruled out a bad air pump, if what you say is true. First step is to check your power steering pump fluid level. It is likely low. The pump may not be bad...yet. Unscrew the dipstick and if it's low (or you don't see any level register at all in the event it is REAL low), put fluid in. Add fluid till the level is between the two marks, when the car is at operating temp. Also turn the wheel back and forth a couple of times before turning off the engine before checking. A hundred bucks says adding fluid will cure your problem. But also check for leaks.

----- Kill ratio of Palestinian children to Israeli children 5.7-to-1, Israel's favor. Kill ratio of all Palestinians to Israelis: over 3-to-1.

---------

"Don't worry about American pressure on Israel. We, the Jewish people, control America, and the Americans know it." ---Israeli Prime Minister Ariel Sharon, 2001

Thanks very much! I added fluid to the power steering and the noise has gone away!

Thanks all for pointing me in the right direction!