Turbocharger

How you know it is this

• A loss of power, often with limp mode
• A whistle or siren rising with boost
• Blue smoke, especially on overrun — oil past the turbo seals
• Oil in the intercooler or the charge pipes
• A rattle from the turbo, or visible shaft play

Worth knowing before you buy

• A turbo almost never fails on its own. Oil starvation or dirty oil kills it, so the feed line, the return line and the oil condition all have to be checked or the new one goes the same way.
• Fitting a turbo without cleaning the intercooler and charge pipes of old oil means that oil gets drawn into the new one.
• Reconditioned and new are both available and the difference is large. Worth quoting both.
• Variable-geometry turbos have an actuator that fails far more often than the turbo. Have that checked before condemning the unit.

Rest of the forced induction

• Turbo actuator and wastegate
• Turbo oil feed and return lines
• Supercharger and clutch
• Intercooler
• Charge pipes and hoses
• Boost pressure sensor
• Diverter and blow-off valve