Exhaust Gas Recirculation Monitor

BACKGROUND
Exhaust Gas Recirculation (EGR) is a method of reducing oxides of nitrogen (NOx) emissions by introducing non-combustible exhaust gases into the combustion chamber. These gases absorb heat and reduce the high cylinder operating temperatures where NOx is most likely to occur. Lower combustion chamber temperatures result in lower NOx emissions.





OPERATION
The EGR system consists of a vacuum solenoid, back pressure transducer, and a vacuum operated valve. When activated, the solenoid allows vacuum to act upon the transducer. Negative exhaust back pressure allows manifold vacuum from the solenoid to vent to the atmosphere. Positive exhaust back pressure causes the transducer diaphragm to modulate. This allows intake manifold vacuum to reach the EGR valve. The combination of vacuum on one side of the valve diaphragm and exhaust back pressure on the other allows exhaust gases to be introduced into the intake manifold.

An EGR system that is stuck in the closed position prevents the system from decreasing NOx emissions. A system stuck in the open position can increase hydrocarbon emissions, fuel consumption, and produce rough engine operation.





To detect operation of the system, automatic fuel compensation is temporarily disabled, the EGR solenoid is turned off, and the O2 compensation control is monitored. If the EGR system is operating properly, turning it off shifts the air/fuel ratio in the lean direction. O2 sensor data should indicate an increase in oxygen in the exhaust gases, and cause the short term control to shift to rich. The amount of the shift indirectly monitors the operation of the system.

ENABLING CONDITIONS
The following conditions must be met before the EGR monitor will run:

^ Engine temperature is greater than 170° F
^ More than three minutes have passed since start-up
^ Engine RPM is between 2,248 and 2,688 (auto) or between 1,952 and 2,400 (manual)
^ MAP voltage is between 1.80 and 2.70
^ TPS voltage is between 0.6 and 1.8
^ Vehicle speed exceeds 40 MPH

Short term O2 controller is adjusting pulse width by less than + 4.4%

PENDING
The EGR monitor does not run if the MIL is illuminated due to one of the following:

^ Misfire DTC
^ O2 monitor DTC
^ Upstream O2 heater DTC
^ Fuel system rich/lean DTC
^ Upstream O2 shorted high
^ Vehicle is in limp-in mode due to MAP, TPS, or engine temperature DTC
^ Vehicle speed sensor DTC
^ EGR solenoid DTC
^ Cam or crank sensor DTC

CONFLICT
The EGR monitor does not run if:

^ The fuel system rich intrusive test is in progress
^ Purge monitor is in progress
^ Catalyst monitor is in progress
^ Time since start is less than 60 seconds
^ One trip misfire maturing code
^ One trip O2 monitor maturing code
^ One trip upstream O2 heater maturing code
^ One trip fuel system rich maturing code
^ One trip fuel system lean maturing code

SUSPEND
Results of the EGR monitor not are not recorded until the O2 monitor passes.

This monitor is performed once each trip. If the measured change in the short term shift during the test is less than 7.4% or greater than 20.5%, the monitor fails, and a maturing code is stored. The MIL illuminates and a DTC is stored if the monitor is outside this range for a total of two consecutive trips. The message on the diagnostic scan tool screen appears as follows:

EGR System Failure
Flash Code - 32 J 2012 Code - P 0401

The MIL extinguishes if the EGR monitor passes for three consecutive trips. The DTC is erased after 40 successful warm-up cycles.

Malfunction of the EGR monitor could possibly be caused by problems with any of the following mechanical components:

^ EGR valve assembly
^ EGR tube
^ Wiring harness and connectors
^ Vacuum hoses