DTC P0401: EGR Flow Insufficient: Description

The Exhaust Gas Recirculation (EGR) valve consists of a pintle valve, which moves by the use of an internal solenoid, and an internal position sensor (potentiometer) used to determine pintle valve position. The ECM controls the solenoid by supplying it ground whenever exhaust gas needs to be recirculated into the intake manifold. The ECM monitors the EGR solenoid and position sensor circuit for correct voltage levels at certain time. The ECM also monitors the flow rate of exhaust gas through the EGR valve by using the MAP sensor. After certain conditions have been met, the ECM will compare the MAP sensor signal voltage change and its steady state value to a modeled MAP sensor signal value after the EGR valve has been commanded On. This once per ignition cycle test is based off of the narrow engine speed and load range listed under DTC parameters. DTC P0401 sets when the MAP sensor signal voltage change or its steady state value is below a certain threshold (indicating too little change in intake manifold pressure) when the EGR valve is commanded to a certain duty cycle.