BMW fitted both mechanical and hydraulic belt tensioners to their models, and the only way to know which one has been fitted to your BMW is with a visual inspection. This particular roller attaches to the hydraulic tensioner (the one that looks as if it has a shock absorber attached to it), and keeps the main drive belt tight, ensuring there is enough traction for the water pump and alternator to work. Something as simple as a loose belt can cause a failure of both the motor and its electrical systems. 

Please note that this pulley cannot be used to replace the stand-alone idler pulley on the main drive belt run for most models, nor can it be fitted to the mechanical belt tensioner. This part can only be fitted to a hydaulic tensioner system. Please contact us if you have any questions.

OEM Part Number: 11281748131
Ref Part Number: 14-0492
INA Part Number: 532 0001 10