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 powertrain control module (PCM) controls the solenoid by supplying it ignition voltage whenever exhaust gas needs to be recirculated into the intake manifold. The PCM monitors the EGR solenoid and position sensor circuit for correct voltage levels at certain times. The PCM also monitors the flow of exhaust gas through the EGR valve by using the manifold absolute pressure (MAP) sensor. During deceleration, the EGR valve is normally closed. However, the PCM will run a flow test by opening the EGR valve and monitoring the change in the MAP signal voltage. DTC P0401 sets when the change in the MAP signal voltage is below a certain threshold when the EGR valve is being commanded ON during the deceleration.
DTC Parameters
DTC P0401 will set if the PCM determines EGR flow to be restricted based on engine speed and barometric pressure using the MAP sensor when:
| • | The engine speed is between 1250-2600 RPM. |
| • | The vehicle speed is greater than 56 km/h (35 mph). |
| • | The throttle position (TP) angle is 0 percent (vehicle in decel). |
| • | The engine coolant temperature (ECT) is greater than 70°C (150°F). |
| • | No cam, crankshaft position (CKP), ECT, EGR solenoid, 5-volt reference, idle air control (IAC), intake air temperature (IAT), MAP, misfire, PCM internal fault, TP or vehicle speed DTCs have been set. |
DTC P0401 diagnostic runs once per ignition cycle for 1 second during deceleration once the above conditions have been met.
DTC P0401 is a type A DTC.
Diagnostic Aids
Verify the MAP sensor reads correctly at idle (between 1-1.5 volts). If the MAP sensor is skewed or faulty, DTC P0401 may set.
The most likely cause of this DTC is carbon buildup around the EGR valve or a blocked EGR passage.
Remove the EGR valve and check for a blocked passage and for carbon buildup around the EGR pintle valve. Clean or replace the EGR valve and/or clean EGR passage.
