Electric Exhaust Gas Recirculation (EEGR) System Monitor

ELECTRIC EXHAUST GAS RECIRCULATION (EEGR) SYSTEM MONITOR

EEGR System Monitor:

The EEGR 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 engine coolant temperature (ECT) or cylinder head temperature (CHT), intake air temperature (IAT), throttle position (TP), crankshaft position (CKP), mass air flow (MAF), and manifold absolute pressure (MAP) sensors is required to activate the EGR system monitor. Once activated, the EGR system monitor carries out each of the tests described below during the engine modes and conditions indicated. Some of the EGR system monitor tests are also carried out during an on-demand self-test.

The EEGR monitor consists of an electrical and functional test that checks the stepper motor and the EEGR system for correct flow. The powertrain control module (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 4 electric stepper motor coils and circuits to the PCM. A concern 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 concern has been detected, the EEGR system is disabled, setting diagnostic trouble code (DTC) P0403. Additional monitoring is 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 carried out. The flow test is carried out 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 concern 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 2 different values: MAP - the analog MAP sensor reading, and inferred MAP - calculated from the MAF sensor, throttle position and RPM. 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 correctly 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 the 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 IMAP 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, 7 such ON/OFF samples are taken. After all the samples have been taken, the average EGR-ON MAP, EGR-ON IMAP, EGR-OFF MAP and EGR-OFF IMAP values are stored.

The difference between the EGR-ON and EGR-OFF value is calculated as follows:
- MAP-delta equals EGR-ON MAP - EGR-OFF MAP (analog MAP)
- IMAP-delta equals EGR-ON IMAP - EGR-OFF IMAP (inferred MAP)

If the sum of MAP-delta and IMAP-delta exceeds a maximum threshold or falls to less than a minimum threshold, DTC P0400 (high or low flow concern) 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 carried out 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 to decrement, and if conditions permit, attempts to complete the EGR flow monitor. If the timer reaches 800 seconds, the EEGR flow test is disabled for the remainder of the current driving cycle and the EGR monitor is set to a ready condition.

A DTC P1408, like the P0400, indicates a EGR flow concern (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.