Note. For circuit reference, see WIRING DIAGRAMS article.
Scheme 9
Circuit Description
Exhaust Gas Recirculation (EGR) system controls formation of NOx emissions by recirculating exhaust gases into combustion chamber. PCM uses expected changes in Manifold Absolute Pressure (MAP) sensor readings in order to evaluate performance of EGR system. PCM applies full manifold vacuum to EGR valve while monitoring MAP sensor signal. PCM suspects that EGR valve flow is incorrect when monitored MAP sensor pressure change is either too large or too small.