Download CAUTION: If ECM replacement is instructed in following testing, always ensure ECM connectors and ground circuit are okay. If either are suspect, repair and repeat testing to confirm ECM malfunction. Circuit Description The EGR system recirculates exhaust gas through intake system to reduce combustion temperature and NOx emissions. The amount of EGR valve opening is regulated by the EGR vacuum modulator according to engine load. Vacuum source to valve is controlled by the Vacuum Switching Valve (VSV), which is controlled by The EGR valve is closed (VSV on) under the following conditions: Engine is not warmed up. Vehicle under deceleration. Light engine load. Engine racing.
Home Auto Repair 1997 Toyota Corolla DTC P0401: INSUFFICIENT EXHAUST GAS RECIRCULATION (EGR) FLOW DETECTED