EGR System Module
The ESM EGR system is an updated DPFE system. It functions in the same manner as the conventional DPFE system, however the various system components have been integrated into a single component called the EGR System Module (ESM). See Fig 1 and Fig 2 . The flange of the valve portion of the ESM bolts directly to the intake manifold with a metal gasket that forms the measuring orifice. This arrangement increases system reliability and response time. By relocating the EGR orifice from the exhaust to the intake side of the EGR valve, the downstream pressure signal measures Manifold Absolute Pressure (MAP). The system provides the PCM with a differential DPFE signal, identical to the traditional DPFE system.
The Delta Pressure Feedback EGR Monitor is a series of electrical tests and functional tests that monitor various aspects of EGR system operation.
First, the Delta Pressure Feedback EGR (DPFE) sensor input circuit is checked for out of range values (P1400/P0405 and P1401/P0406). The Electronic Vacuum Regulator (EVR) output circuit is checked for opens and shorts (P1409/P0403).
EGR normally has large amounts of water vapor that are the result of the engine combustion process. During cold ambient temperatures, under some circumstances, water vapor can freeze in the DPFE sensor, hoses, as well as other components in the EGR system. In order to prevent MIL illumination for temporary freezing, the following logic is used:
- If an EGR system malfunction is detected above 32°F, the EGR system and the EGR monitor is disabled for the current driving cycle. A DTC is stored and the MIL is illuminated if the malfunction has been detected on two consecutive driving cycles.
- If an EGR system malfunction is detected below 32°F, only the EGR system is disabled for the current driving cycle. A DTC is not stored and the I/M readiness status for the EGR monitor will not change. The EGR monitor, however, will continue to operate. If the EGR monitor determined that the malfunction is no longer present (i.e., the ice melts), the EGR system will be enabled and normal system operation will be restored.
After the vehicle is started, during vehicle acceleration, the differential pressure indicated by the DPFE sensor at zero EGR flow is checked to ensure that both hoses to the DPFE sensor are connected. Under this condition, the differential pressure should be zero. If the differential pressure indicated by the DPFE sensor exceeds a maximum threshold or falls below a minimum threshold, an upstream or downstream DPFE hose malfunction is indicated (P1405 P1406).
After the vehicle has warmed up and normal EGR rates are being commanded by the PCM, the low flow check is performed. Since the EGR system is a closed loop system, the EGR system will deliver the requested EGR flow as long as it has the capacity to do so. If the EVR duty cycle is very high (greater than 80% duty cycle), the differential pressure indicated by the DPFE sensor is evaluated to determine the amount of EGR system restriction. If the differential pressure is below a calibratable threshold, a low flow malfunction in indicated (P0401/P0406).
Finally, the differential pressure indicated by the DPFE sensor is also checked at idle with zero requested EGR flow to perform the high flow check. If the differential pressure exceeds a calibratable limit, it indicates a stuck open EGR valve or debris temporarily lodged under the EGR valve seat (P0402).
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 less than 22.5 in. 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. Vehicles will require two such driving cycles for the EGR Monitor I/M Readiness bit to be set to a "ready" condition.