Exhaust Gas Recirculation (EGR) System Monitor

EXHAUST GAS RECIRCULATION (EGR) SYSTEM MONITOR

The EGR system is a closed loop EGR valve position control system. It uses an exhaust pressure (EP) sensor, a manifold absolute pressure (MAP) sensor and a speed density estimate of total mass flow and derives a desired EGR valve position based on a desired EGR flow percentage. The EGR monitor is a series of electrical tests and functional tests that monitor various aspects of EGR system operation. An intrusive test is used to detect low EGR flow rates (P0401) and high EGR flow rates (P0402). The EGR valve is closed and volumetric efficiency is estimated using mass air flow (MAF), MAP, and intake air temperature 2 (IAT2). Airflow through the engine is then calculated using the estimated volumetric efficiency, MAP and engine RPM. At this point, the EGR valve is commanded to open and the change in MAF is observed. The EGR flow rate can now be determined by looking at the difference between the speed density engine flow rate and MAF rate. The EGR flow rate is divided by the engine flow to estimate desired EGR percentage.

The typical EGR low flow monitor entry conditions include:
- Diesel particulate filter regeneration not requested
- Pressure ratio (MAP/EP) across EGR valve is less than 1
- No change in engine RPM
- No change in indicated torque setpoint
- Engine RPM is between 600 RPM and 800 RPM
- Indicated torque setpoint is between 45 Nm (33 lb-ft) and 174 Nm (128 lb-ft)
- Power take off (PTO)/auxiliary idle control system not active

The DTC P0401 is set when the delivered EGR is 28% less than expected for the operating conditions. EGR rates are specified as a function of engine RPM and indicated torque setpoint.

The typical EGR high flow monitor entry conditions include:
EGR low flow monitor not active
- Diesel particulate filter regeneration not requested
- Fuel mass verification strategy not active
- Pressure ratio (MAP/EP) across EGR valve is less than 1
- No change in engine RPM.
- No change in indicated torque setpoint
- Engine RPM is between 600 RPM and 800 RPM
- Indicated torque setpoint is between 45 Nm(33 lb-ft) and 174 Nm (128 lb-ft)
- Power take off (PTO)/auxiliary idle control system not active

The diagnostic trouble code (DTC) P0402 is set when the delivered EGR is 20% greater than expected for the operating conditions. EGR rates are specified as a function of engine RPM and indicated torque setpoint.