OBD Operation Summary for 6.7L Diesel - MotorCraftService.com

EXHAUST GAS RECIRCULATION (EGR) SYSTEM MONITOREGR Rate System MonitorThe EGR system is a closed loop EGR control system that uses an Air System Model EGR to estimate the percentof EGR in the cylinder. Airflow into the engine is modeled using a Mass Airflow Sensor (MAF) and a model ofairflow over the throttle restriction. EGR mass flow is then calculated as the difference between the cylinder chargefrom the speed-density equation and this model of the mass airflow after the throttle. This model value of the actualEGR flow based on measured values is compared with the estimated EGR rate computed by the EGR ratecontroller. The EGR rate controller calculates the mass flow based on an open area estimate at the EGR valveand a modeled value of mass flow per open area. EGR open area estimate uses a combination of the areacalculated from the modeled EGR rate and a calibrated curve of the expected open area based on EGR valveposition.Once the engine is warm and the system in closed-loop EGR control, the monitor awaits calibrated enginespeed/load conditions selected for robust detection of high flow and low flow faults. When the engine enters theoperational regime for robust detection, the calculated rate deviation (modeled – controller estimate) is comparedto thresholds that are calibrated as a function of speed/load. An up/down counter is used that counts upward whenthe rate deviation exceeds the calibrated threshold and counts downward when the deviation falls below thethreshold for the case of high flow. Similarly, the up/down counter counts upward when the rate deviation fallsbelow a calibrated threshold and counts downward when it rises above the threshold for the case of low flow.Once the debounce counter exceeds a calibrated threshold for either high or low flow then a malfunction isdetected. A low flow malfunction indicated (P0401) and a high flow malfunction in indicated (P0402)EGR Flow Check Operation:DTCsMonitor ExecutionMonitor SequenceMonitoring DurationP0401 – Insufficient EGR FlowP0402 – Excessive EGR FlowContinuousNoneTypical EGR Flow Check Entry Conditions (High Flow Detection):Entry Condition Minimum MaximumEngine Torque 100 Nm 600 NmEngine RPM 600 rpm 2500 rpmEngine Coolant Temperature 70 deg C 100 deg CEGR Valve Position 0% 6%EGR Rate Desired Value 0% 15%FORD MOTOR COMPANY REVISION DATE: FEBRUARY 9, 2012 09.01.00.02-PAGE 44 OF 157