EGR System Monitor - DPFE and ESM

EXHAUST GAS RECIRCULATION (EGR) SYSTEM MONITOR - DELTA PRESSURE FEEDBACK (DPFE) EGR AND EGR SYSTEM MODULE (ESM) EGR

EGR System Monitor - Delta Pressure Feedback EGR:

EGR System Monitor - EGR System Module EGR:

The EGR System 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 and after certain base engine conditions are satisfied. Input from the ECT, CHT, IAT, TP and CKP sensors is required to activate the monitor. Once activated, the EGR System Monitor will perform each of the tests described below during the engine modes and conditions indicated. Some of the EGR System Monitor tests are also performed during on demand self-test.

NOTE: The Delta Pressure Feedback EGR (DPFE) sensor, EGR Vacuum Regulator (EVR) solenoid, Manifold Absolute Pressure (MAP) sensor and the EGR valve itself are integrated into one unit in the ESM EGR assembly. The ESM is not serviceable. If any one component fails within the ESM, the entire ESM assembly must be replaced.

1. The Delta Pressure Feedback 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 DTCs associated with this test are DTCs P0405 or P1400 and P0406 or P1401.

2. The EVR solenoid is continuously tested for opens and shorts. The monitor looks for an EVR circuit voltage that is inconsistent with the EVR circuit commanded output state.

The DTC associated with this test is DTC P0403 or 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 off to determine if EGR flow is present at idle.

The DTC associated with this test is DTC 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 DTC 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. This is a system test and may trigger a DTC for any fault causing the EGR system to fail.

The DTC associated with this test is DTC P0401. DTC P1408 is similar to P0401 but performed during KOER Self-Test conditions.

6. The MIL is activated after one of the above tests fails on two consecutive drive cycles.

ELECTRIC EXHAUST GAS RECIRCULATION (EEGR) SYSTEM MONITOR

EEGR System Monitor - Electric EGR System:

The Electric or "Stepper" Motor EGR System 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 and after certain base engine conditions are satisfied. Input from the ECT or CHT, IAT, TP, CKP, MAF, and MAP sensors is required to activate the EGR System Monitor. Once activated, the EGR System Monitor will perform each of the tests described below during the engine modes and conditions indicated. Some of the EGR System Monitor tests are also performed during on demand self-test

The Electric EGR Monitor consists of an electrical and functional test that checks the stepper motor and the EEGR system for proper flow. The PCM controls the EEGR valve by commanding from 0 to 52 discreet increments or "steps" to get the valve from fully closed to fully open. The stepper motor electrical test is a continuous check of the four electric stepper motor coils and circuits to the PCM. A malfunction is indicated if an open circuit, short to power or short to ground has occurred in one or more of the stepper motor coils or circuits for a calibrated period of time. If a malfunction has been detected, the EEGR system will be disabled, setting the KOER, and Continuous P0403 DTC. Additional monitoring will be suspended for the remainder of the drive cycle, or until the next engine startup.

After the vehicle has warmed up and normal EEGR flow rates are being commanded by the PCM, the EEGR flow check is performed. The flow test is performed once per drive cycle when a minimum amount of exhaust gas is requested and the remaining entry conditions required to initiate the test are satisfied. If a malfunction is detected, the EEGR system as well as the EEGR monitor is disabled until the next engine startup.

The EEGR flow test is done by observing the behavior of two different values: MAP - the analog MAP sensor reading, and inferred MAP - calculated from the Mass Air Flow Sensor, throttle position, rpm, etc. During normal, steady-state operating conditions, EEGR is intrusively commanded ON to a specified percentage. Then, EEGR is commanded OFF. If the EEGR system is working properly, there is a significant difference in both the observed and the calculated values of MAP, between the EGR-ON and the EGR-OFF states.

When flow test entry conditions have been satisfied, EEGR is commanded to flow at a calibrated test rate (about 10%). At this time, the value of MAP is recorded (EGR-ON MAP). The value of inferred MAP EGR-ON MAP is also recorded. Next the EEGR is commanded off (0%). Again, the value of MAP is recorded (EGR-OFF MAP). The value of EGR-OFF IMAP is also recorded. Typically, seven such ON/OFF samples are taken. After all the samples have been taken, the average EGR-ON MAP, EGR-ON MAP, EGR-OFF MAP and EGR-OFF IMAP values are stored.

Next, the difference between the EGR-ON and EGR-OFF value is calculated:

- MAP-delta = EGR-ON MAP - EGR-OFF MAP (analog MAP)
- IMAP-delta = EGR-ON IMAP - EGR-OFF IMAP (inferred MAP)

If the sum of MAP-delta and IMAP-delta exceeds a maximum threshold or falls below a minimum threshold, a P0400 (high or low flow malfunction) is registered.

As an additional check, if the EGR-ON MAP exceeds a maximum threshold (BARO, a calibrated value), DTC P0400 (low flow) is set. This check is performed to detect reduced EGR flow on systems where the MAP pickup point is not located in the intake manifold, but is located just upstream of the EEGR valve in the EEGR delivery tube.

NOTE: BARO is inferred at engine startup using the KOEO MAP sensor reading. It is updated during high, part-throttle or high rpm engine operation.

If the inferred ambient temperature is less than -7°C (20°F), greater than 54°C (130°F), or the altitude is greater than 8,000 feet (BARO less than 22.5 in-Hg), the EEGR flow test cannot be reliably done. In these conditions, the EEGR flow test is suspended and a timer starts to accumulate the time in these conditions. When 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 EEGR flow test is disabled for the remainder of the current driving cycle and the EGR Monitor will be set to a "ready" condition.

A DTC of P1408, like the P0400, will indicate a EGR flow failure (outside the minimum or maximum limits) but is only set during the KOER self test. The P0400 and P0403 are MIL codes. P1408 is a non-MIL code.