Detection Condition

DTC P0401 indicates self-test has detected insufficient EGR flow. EGR system receives signals from ECT, IAT, TP, MAF and CKP sensors to provide PCM with information on engine operating conditions. Before EGR system is activated, engine must be warm, stable and running at a moderate load and RPM. PCM deactivates EGR during idle, extended wide open throttle or when a failure is detected in an EGR component or EGR required component. EGR Vacuum Regulator (EGRVR) solenoid receives a variable duty cycle signal from PCM. The higher duty cycle, the more vacuum the solenoid diverts to the EGR valve. An increase in vacuum acting on EGR valve diaphragm overcomes a spring and begins to lift EGR valve pintle off its seat, allowing exhaust gas to enter intake manifold. One side of the EGR orifice tube is exposed to exhaust gas backpressure and the other side is exposed to the intake manifold, causing a pressure drop across the orifice whenever there is EGR flow. When EGR valve closes, there is no longer any flow across the metering orifice and pressure on both sides of the orifice is the same. The Differential Pressure Feedback EGR (DPFEGR) measures actual pressure drop across the metering orifice and relays a proportional voltage signal (0-5 volts) to PCM.