Features   |   Identification   |   Component Locations   |   How it Works Exhaust Gas Recirculation An Exhaust Gas Recirculation (EGR) system is used with the MPI system. The EGR system is used to reduce nitrous oxide (NOx) emissions. The system recirculates a small portion of exhaust gas into the intake mixture. The exhaust gas is non-combustible and takes up a small space in the intake charge. The result is lower combustion temperatures and reduced NOx. The EGR does not operate at idle because NOx emissions are low during this time. The following inputs are used for the EGR system: Engine speed Engine load Engine coolant temperature Signal from idle switch The Exhaust Gas Recirculation is controlled by the ignition map in the MPI control unit. This allows precise regulation of the exhaust gas recirculation flow. An EGR Frequency Valve (N18) is connected to the intake manifold and operated by the MPI control unit. The frequency valve regulates the amount of vacuum supplied to the EGR valve. By regulating the amount of vacuum to the EGR valve, its opening position and therefore the amount of exhaust gas recirculated can be accurately controlled. The valve is located under the Mass Air Flow (MAF) sensor next to the intake manifold changeover valve. Substitute Function Thereare no substitute functions for the EGR frequency valve. If the valve does not receive power or ground, exhaust gas recirculation will not occur. Self-diagnosis The ECU recognizes the following: Short circuit to positive Open circuit/short to ground EGR Temperature Sensor G98 The EGR temperature sensor is located on the outlet side of the EGR valve. The sensor is used to inform the MPI control unit that the EGR valve is functioning. The sensor measures the temperature of the recirculated exhaust gas. The EGR temperature sensor is for fault recognition only. If the EGR valve, temperature sensor, or wiring fails, the fault is stored in the MPI control unit's permanent fault memory and the 'check engine' light illuminates.

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