Theory Of Operation

WARNING: This page is about a different variant/trim than selected.

GENERAL OPERATION: The Powertrain Control Module (PCM) monitors the intake air flow, and controls the variable geometry turbocharger (VGT) position to obtain the correct amount of fresh air and exhaust gas recirculation (EGR) for the injected amount of fuel. The PCM compares the actual air flow (calculated using multiple sensors in the intake air system - Mass Air Flow, Boost Pressure, and Temperature sensors) versus the desired air flow. If the difference between these two is greater than a calibrated amount, for a calibrated period of time, the under boost, or over boost diagnostic trouble code (DTC) will be set. Anything that affect air flow (exhaust or intake) through the engine can cause an under boost or over boost condition. This can include leaks or blockages in the intake air system plumbing, or the exhaust system. These system should be carefully inspected before condemning any component.

The main component used to manage boost is the Variable Gate Turbocharger (VGT) Assembly. The base VGT boost pressure is managed through the position of the turbine vanes. When the PCM is trying to build boost pressure (to protect from an under boost condition), it closes down the effective area of the VGT turbine vanes to increase VGT speeds. When the PCM is trying to reduce boost pressure (to protect from an over boost condition), it opens up the effective area of the VGT turbine vanes reducing the VGT speed.

Fuel economy and emissions are improved when the engine is allowed to reach a higher temperature. Engine performance and torque are increased when the engine is running at a cooler temperature. The PCM balances operates the Turbocharger system in two separate modes to balance between efficiency and performance. Based on atmospheric conditions and operating needs the Turbocharger system can operate in either Rapid Heat-Up or Standard Heat-Up mode. Regardless of which mode the system is operating in the under boost and over boost diagnostics are the same. However, a different DTC will set a based on which mode of operation the system was in when a fault occurs.

The PCM sets the P2D2F-00 DTC when there is an under boost occurrence during the Rapid Heat-Up mode.
The PCM sets the P0299-00 DTC when there is an under boost occurrence during the Standard Heat-Up mode.
Because the PCM switches between Rapid Heat-Up and Standard Heat-Up mode, both DTCs may be present when under boost is detected. Both DTCs have the same Diagnostic content.