Exhaust Gas Recirculation System Monitor

PURPOSE
The Exhaust Gas Recirculation (EGR) system monitor is a self-test strategy within the Powertrain Control Module (PCM) that tests the integrity of the circuitry, components and hoses that make up the EGR system and determines EGR flow rate errors. The EGR monitor may directly or indirectly detect a malfunction in any of the EGR system components and control circuitry.

OPERATION
The EGR monitor uses the input from the Differential Pressure Feedback Electronic (DPFE) sensor as feedback to monitor the EGR system. The monitor is capable of checking the DPFE sensor, EVR solenoid, electrical circuits, pressure signal hoses, and EGR valve. Other Electronic Engine Control-V (EEC-V) components provide conditions to the EGR control system, but do not have direct input to the EGR monitor. For example, if a failure occurs in the Engine Coolant Temperature (ECT), Intake Air Temperature (IAT), Throttle Position (TP), or Mass Air Flow (MAF) sensor, the EGR system will be disabled and the monitor will not be executed.

The EGR monitor will continuously check the integrity of the DPFE sensor and circuit to the PCM. If the DPFE sensor voltage input is within the operating range, the DPFE sensor becomes the tool for the remaining EGR system checks.

A check for EGR flow at idle is done to determine if the valve is open.

As the vehicle accelerates and exhaust back pressure increases, a check of the DPFE signal pressure hoses is performed to determine disconnects, leaks, plugging, or reversed hoses. This check is performed only once per drive cycle.

EGR flow rate is checked during a steady speed and load state when EGR demand is high. During this state, a comparison is made between the EGR flow rate indicated by the DPFE sensor and a minimum value for the EGR flow rate for this state. A value less than the minimum value identifies a restricted EGR valve or a non-operating EGR system.


Malfunction Indicator Lamp (MIL) and Diagnostic Trouble Codes (DTC's)
After a malfunction has been present for two drive cycles, the DTC is stored in the PCM memory and the MIL is turned on. Once the DTC has been stored in memory, the MIL will stay on as long as the malfunction exists. The MIL is turned off after three consecutive trips without the same malfunction being detected provided no other fault codes are stored that would independently illuminate the MIL. The DTC will be erased from memory after 40 warm-up cycles without the malfunction being detected after the MIL is turned off. Another method of erasing the DTC is initiating an On-Board Diagnostics II (OBD II) PCM reset.