Theory Of Operation

WARNING: This page is about a different car, the 2015 Fiat 500. However, it is still accessible from the selected car via links, so may be relevant.

When the accelerator is closed suddenly, excessive boost pressure can build up between the Turbocharger and the Throttle Body which can cause damage to the Turbocharger. This can occur because the compressed air created by the Turbocharger has no place to go. This results in compressor surge. The Powertrain Control Module (PCM) detects this pressure increase via input from the Boost Pressure Sensor. The Boost Pressure Sensor operates as a typical three wire sensor. The PCM provides a 5-volt supply and sensor return circuit to the Boost Pressure Sensor and receives a feedback voltage on the signal circuit. The Turbocharger Surge Valve is responsible for venting the boost pressure between the Turbocharger and Throttle Body during sudden deceleration. The Turbocharger Surge Valve is normally spring loaded closed. When the PCM receives an input signal from the Boost Pressure Sensor that the pressure is above a calibrated amount, the PCM grounds the Turbocharger Surge Valve Control circuit which electrically opens the valve and routes the excess pressure between the Turbocharger and the Throttle Body back to the inlet of the Turbocharger, relieving the pressure and preventing compressor surge.