For 1990-2009 cars

### Circuit 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 engine control module (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 times. The ECM also monitors the flow rate of exhaust gas through the EGR valve by using the manifold absolute pressure (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 changes 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.

### Conditions for Setting the DTC

DTC P0401 will set if the ECM determines EGR flow to be restricted by comparing the MAP sensor signal voltage change along with a steady state value to a modeled value when:

• | The condition exists for longer than 9 seconds continuously or for a total of 9 seconds up to 3 independent tests.

• | The EGR solenoid is commanded to a 100 percent duty cycle.

• | The engine speed is between 1,600-2,200 RPM.

• | The engine load is between 35-65 percent.

• | The engine load change rate is less than 0.35 percent.

• | The accumulated air mass is greater than 0.5 kg since engine start.

• | The altitude is less than 2 750 meters (9,023 ft).

DTC P0401 diagnostic runs once per ignition cycle up to 9 seconds once the above conditions have been met. However, the diagnostic may take only 3 seconds to pass.

DTC P0401 is a type B DTC.

### Diagnostic Aids

Important: If any MAP, EGR sensor, or EGR solenoid DTCs are also set, diagnose those DTCs first.

This DTC may set if the MAP sensor air tube is plugged or partially plugged or if the sensor has a leak around the sealing grommet.

Important: It takes up to a 40 percent or more duty cycle to make the EGR valve move.

Remove the EGR valve and check the EGR gasket for damage and EGR passage for a carbon blocked condition. If OK, replace the EGR valve.