What does it mean?
The turbocharger is essentially an exhaust-driven air pump. It uses turbine and compressor wheels to use exhaust pulses from the engine to propel the turbine wheel which is paired with the compressor wheel. Which in turn creates pressure within the intake system (AKA Boost). Creating boost increases volumetric efficiency. In other words, increasing the amount of air that enters the combustion chamber. The ECU will activate this code the moment it detects the turbine shaft speed going faster then desired. It does this by monitoring the turbocharger speed sensor. Often times, the turbocharger speed sensor is a variable reluctant speed sensor. The ECM interprets the sensor reading , if speed is higher than limit it activates this code.