Theory Of Operation

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

The EGR Airflow Control Valve is a pulse width modulated output, controlled by the Powertrain Control Module (PCM). The EGR Airflow Control Valve is used to control the ratio of fresh air flow to EGR gas air flow. The PCM monitors this ratio with the Mass Air Flow Sensor. The Mass Air Flow Sensor feedback is very prominent in determining the position of the EGR Airflow Control Valve. If the Mass Air Flow Sensor feedback does not match what the PCM is expecting to see when EGR air flow is requested, it can effect the operation of the EGR Valve and the EGR Airflow Control Valve. This can occur if the Mass Air Flow Sensor feedback is faulty or inaccurate, even if no DTCs are actively set. The EGR system and Diesel Particulate Filter regeneration is disabled when the fault is active.

There are two separate approaches used for this monitor: The Standard Heat-Up (SHU) and the Rapid Heat-Up (RHU). 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 determines which heat-up mode to use based on various conditions.

The PCM uses the P0401-00 monitor when there is an EGR Airflow Control Valve flow-insufficient occurrence during the SHU mode.

The PCM uses the P04DD-00 monitor when there is an EGR Airflow Control Valve flow-insufficient occurrence during the RHU mode.

Because the PCM switches between SHU and RHU mode, both DTCs may be present when flow-excessive is detected. Both DTCs have the same Diagnostic content.