Electric Exhaust Gas Recirculation (EEGR) System Monitor

Electric Exhaust Gas Recirculation (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 afier certain base engine conditions are satisfied. Input from the engine coolant temperature (ECT) or cylinder head temperature (CHT) intake air temperature (IAT) throffle 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 will carry 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 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 4 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 DTC P0403. 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 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 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 2 different values: MAP - the analog MAP sensor reading and inferred MAP - calculated from the MAF 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 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.

Then 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 to less than a minimum threshold DTC 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 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 will attempt 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 will be set to a ready condition.

A DTC 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.