Old thread but considering that the Aux Fan for M54 cars (E39, E53 etc.) is expensive ($400-$600), does anyone know the EXACT cause of the Aux Fan failure?

1. Is it seized bearing causing overheat of the electronics?
2. Or the electronics goes bad with age?

If the cause is #1 above, then routine maintenance such as every 8 years/80K miles or so, one should disassemble the fan motor and lubricate the bearings inside to prevent seizing?

Just a thought...

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