Exhaust Gas Recirculation Monitor/Differential Pressure Feedback EGR

The differential pressure feedback EGR monitor is an on-board strategy designed to test the integrity and flow characteristics of the EGR system. The monitor is activated during EGR system operation after certain bases engine conditions are satisfied. Inputs from the ECT, IAT, TP and CKP sensors are required to activate the EGR monitor. Once activated, the EGR monitor will perform each of the tests described below during the engine modes and conditions indicated. See Fig 1. Some of the EGR monitor test are also performed during on demand self-test.

1. The D.P.F. EGR sensor and circuit are continuously tested for opens and shorts. The monitor looks for the DPFE circuit voltage to exceed the maximum or minimum allowable limits. The DTC associated with this test are DTCs P1400 and P1401.
2. The EGR vacuum regulator solenoid is continuously tested for open and shorts. The monitor looks for the DPFE circuit voltage that is inconsistent with the EVR circuit commanded output state. The DTC associated with this test is DTC P1409.
3. The test for a stuck open EGR valve or EGR flow at idle is continuously performed whenever at idle (TP sensor indicating closed throttle). The monitor compares the DPFE circuit voltage at idle to the DPFE circuit voltage stored during key on engine of to determine if EGR flow is present at idle. The DTC associated with this test is P0402.
4. The DPFE sensor hoses are tested once per drive cycle for disconnect and plugging. The test is performed with EGR valve closed and during a period of acceleration. The PCM will momentarily command the EGR valve closed. The monitor looks for the DPFE sensor voltage to be inconsistent for a no flow voltage. A voltage increase or decrease during acceleration while the EGR valve is closed may indicate a fault with a signal hose during this test. The DTCs associated with this test are DTCs P1405 and P1406.
5. The EGR flow rate test is performed during a steady state when engine speed and load are moderate and EVR duty cycle is high. The monitor compares the actual DPFE circuit voltage to a desired EGR flow voltage for that state to determine if EGR flow rate is acceptable or insufficient. The DTCs associated with this test are DTCs P0401 and P1408.
6. The Malfunction Indicator Light (MIL) is illuminated after one of the above test fails on 2 consecutive drive cycles.

Fig 1: Identifying EGR Monitor Components (Differential Pressure Feedback)

Courtesy of FORD MOTOR CO.