Symptoms
A whistle or siren that rises with boost, blue smoke under acceleration, loss of power, or oil in the intercooler pipework.
Likely cause
The bearing depends on clean oil at pressure. Contaminated oil, a blocked feed line or shutting a hot engine down immediately all shorten bearing life. Wastegate and actuator faults produce similar symptoms without the bearing being worn.
How should it be checked?
Have the shaft checked for play and the intake tract inspected for oil before assuming the turbo is the fault. Boost-related symptoms often trace back to a hose, a sensor or the wastegate.
How can you check it yourself?
Watch the exhaust from behind while someone accelerates hard from a standstill. Persistent blue smoke is worth asking about.
The question to ask the shop
Is there axial or radial play in the turbo shaft, and is there oil in the intercooler or the charge pipes?