Thanks for the update.

The 1st owner's record showed the air pump was dead at 30K (I bought the car at 112K).

As much as I did the DIY for air pump and trouble-shooting the circuit in the E39 forum, I don't really care about this SAS thingy any more.

- I removed the Relay feeding the air pump
- Placed a small piece of black electrical tape over the CEL light in the dash.
- Once a month, I scan for new CEL codes, if any. In other words, if the only codes I have are SAS-related, then nothing to worry about.

PS: The reason the pump fails so quick is that: it spins at very high speed (? 5000 rpm or so) like a hair blower. It spins for about 30-45 sec or so on cold start.
The electrical motor is made by Johnson Controls and you bet it right, it is made in China.

Search E39 bimmerfest forum, someone bought the cheap 12V pump that is used for pumping air mattress (camping mattress) for about $12 at Walmart.
He wrote a DIY mod in E39 forum, look it up.

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1998 E39 528i 5sp MT
2006 E53 X5 3.0 6sp MT