Plain English Meaning

When the turbocharger or the system that regulates it stops working properly, the engine either loses the extra power the turbocharger was providing, or it gets too much boost and risks internal damage.

Full Definition

A malfunction of the turbocharger system in which the unit can no longer compress induction air to the level required for normal engine performance. Failures generally fall into two categories: those affecting the turbocharger itself (such as bearing failure, turbine or compressor wheel damage, or oil supply loss) and those affecting the system that controls it (such as a stuck or failed wastegate or controller). The result is either a loss of manifold pressure and engine power, or an uncontrolled overboost in which manifold pressure exceeds limits and can damage the engine.