Low Pressure Cooled EGR Monitor (LPEGR)

Prior to the inclusion of Variable Cam Timing (VCT) systems, EGR systems were primarily used to control tailpipe NOx emissions by reducing peak combustion temperatures. Modern day engines with VCT are starting to use external EGR systems to improve vehicle fuel economy by

• Reducing pumping losses
• Reducing heat transfer losses due to lower combustion temperatures
• Potential for high load enrichment reduction
• Potential for compression ratio increase

Starting in 2018 MY Ford will employ a Low Pressure Cooled EGR system for fuel economy and emission reduction. This system includes the following components:

• An H-bridge motor controlled EGR valve & position sensor
• Delta PFE sensor to measure EGR flow
• EGR gas cooler (exhaust to coolant heat exchanger)

Naturally Aspirated EGR will be used on naturally aspirated engines:

• 3.3L 2018MY

Courtesy of FORD MOTOR CO.

The Low Pressure Cooled EGR Monitor is a series of electrical tests and functional tests that monitors various aspects of EGR system operation.

The Exhaust Gas Recirculation Pressure sensor (EGRP) measures the pressure differential across an orifice in the EGR system.

After the vehicle is started, the differential pressure indicated by the DPFE sensor at idle, at zero EGR flow is checked to ensure that both hoses to the DPFE sensor are connected. At idle, the differential pressure should be zero (both hoses see INTAKE MANIFOLD PRESSURE (MAP) SENSOR . If the differential pressure indicated by the sensor exceeds a maximum threshold or falls below a minimum threshold, an upstream or downstream hose malfunction is indicated (P1405, P1406).

The Exhaust Gas Recirculation Valve Control (EGRVC) actuator is used to provide a defined amount of EGR back into the intake manifold. The EGR valve actuator requires an ECU with an H-bridge output and position feedback. The EGR valve actuator is equipped with a non-contacting hall effect position sensor. This sensor is free of mechanical wear, is high-temperature capable, and provides very accurate position feedback.

After the vehicle has warmed up and normal EGR rates are being commanded by the PCM, the low flow check and the high flow check is performed. The EGR flow diagnostics execute once-per-driving cycle and are designed to set a fault when the total mass flow error results in a tailpipe emissions increase above the CARB defined level.

This is achieved by first calculating error tolerance bands around the commanded EGR mass flow and accumulating any error between the measured mass flow and these tolerance bands. This gives separate error accumulations for both insufficient and excessive EGR mass flow. These accumulated errors are then ratio'ed against an accumulation of the total commanded EGR mass flow and compared to a threshold. The threshold is set to represent the point in the drive where an unacceptable emissions level may result (calibrated to the FTP cycle emissions).

Courtesy of FORD MOTOR CO.

If the calculated insufficient flow rate is above a calibrated ratio when compared to actual flow rate a low flow malfunction is indicated (P0401). If the calculated excess flow rate is above a calibrated ratio when compared to actual flow rate a high flow malfunction is indicated (P0402).

I/M Readiness Indication 

If the inferred ambient temperature is less than 32 °F, or greater than 140 °F, or the altitude is greater than 8, 000 feet (BARO < 22.5 "Hg), the EGR monitor cannot be run reliably. In these conditions, a timer starts to accumulate the time in these conditions. If the vehicle leaves these extreme conditions, the timer starts decrementing, and, if conditions permit, will attempt to complete the EGR flow monitor. If the timer reaches 500 seconds, the EGR monitor is disabled for the remainder of the current driving cycle and the EGR Monitor I/M Readiness bit will be set to a "ready" condition after one such driving cycle. Starting in the 2002 MY, vehicles will require two such driving cycles for the EGR Monitor I/M Readiness bit to be set to a "ready" condition.