What commonly causes it
- Oil starvation — often linked to poor servicing history, low oil level, or oil dilution on diesels
- Worn bearings from age and mileage, allowing the turbine shaft to develop play
- A failing wastegate or actuator, affecting boost control without the turbo itself being damaged
- Foreign object damage to the compressor or turbine wheel, sometimes from a failing air filter or intake fault
Warning signs
A whining or whistling noise that rises and falls with engine speed is often the earliest sign. As it progresses, you may notice a loss of power or turbo lag, blue or black smoke from the exhaust, and eventually an engine management light with a boost-related fault code.
Why diagnosis matters before replacement
A wastegate or actuator fault can sometimes be repaired without replacing the whole turbocharger — a significantly cheaper fix. We always diagnose the actual cause first, so you're not paying for a full turbo replacement when a smaller repair would do the job.