Theory Of Operation

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

The Exhaust Gas Recirculation (EGR) system consists of 4 valves. The High Pressure (HP) EGR Valve works in conjunction with a HP EGR Airflow Control Valve to control exhaust gas entering the Intake Manifold. The Low Pressure (LP) EGR Valve works in conjunction with the LP EGR Airflow Control Valve to control exhaust gas entering the (low pressure) feed to the Turbocharger. The EGR system is designed to facilitate maximum efficiency in blending exhaust gases, fresh air, and charge air.

The exhaust gases from the exhaust pipe downstream of the Diesel Particulate Filter (DPF) travel through an in-line cooler to the LP EGR Valve. The LP EGR Valve is opened to allow the exhaust gases to enter the intake air plumbing upstream of the Turbocharger. The LP EGR Valve mixes exhaust gases and fresh air, which is then introduced to the Turbocharger. The LP EGR Airflow Control Valve (sometimes called 'Intake Flap Valve') serves to control overall fresh air flow into the (low pressure) feed to the Turbocharger. The LP EGR Airflow Control Valve depresses intake air pressure to create a pressure differential, or vacuum across the face of the LP EGR Valve. This enhances the ability of the Intake Air System to recirculate exhaust gases at low speed and load conditions. The LP EGR Airflow Control Valve also reduces intake noise and vibration during idle and engine shut off by closing off fresh air flow.

The exhaust gases from the Exhaust Manifold flow directly to the HP EGR Valve. The HP EGR Valve is opened to allow the exhaust gases to enter the Intake Manifold downstream of the HP EGR Airflow Control Valve. There is a cooler between the HP EGR Valve and the Intake Manifold. An EGR Cooler Bypass Valve is used to divert the exhaust gases around the cooler to increase intake air temperature during cold start engine warm up conditions. The HP EGR Airflow Control Valve depresses intake air pressure to create a pressure differential, or vacuum, across the face of the HP EGR Valve. This enhances the ability of the Intake Air System to recirculate exhaust gases at low speed and load conditions. The HP EGR Airflow Control Valve also reduces intake noise and vibration during idle and engine shut off by closing off fresh air flow.

The LP EGR Valve, HP EGR Valve, and HP EGR Airflow Control Valves are controlled by the Powertrain Control Module (PCM) using H-Bridges that reverses the polarity of the two control circuits connected to a DC motor. The PCM utilizes Pulse Width Modulated (PWM) voltage to control the varying loads on these valves during operation. This helps prevent overheating of the DC motors. Each valve has an integrated position sensor. Each position sensor functions as a typical three wire 5-Volt sensor. The PCM receives feedback from the position sensor signal wire.

The LP EGR Airflow Control Valve has a slightly different architecture. This valve is also controlled by the PCM using a PWM ground on one side of the DC motor. The other side of the DC motor is connected to a constant Fused Ignition feed. The LP EGR Airflow Control Valve is defaulted in the open position meaning that the butterfly valve would be wide open if the PWM ground control or Fused Ignition were removed. The LP EGR Airflow Control Valve also has a position sensor integrated into the housing. But this position sensor functions as a two wire 5-Volt sensor. The PCM determines the position of the butterfly valve by monitoring changes in the 5-Volt Signal circuit.