P0401

CIRCUIT DESCRIPTION
The DTC P0401 Exhaust Gas Recirculation (EGR) System diagnostic monitors the operation of the EGR valve. The EGR system controls the formation of oxides of nitrogen (NOx) emissions by recirculating the exhaust gases into the combustion chamber. The powertrain control module (PCM) uses the expected changes in the manifold absolute pressure (MAP) sensor readings in order to evaluate the performance of the EGR system. The PCM sends a signal to the EGR valve while monitoring the MAP sensor signal. The PCM sets DTC P0401 when the monitored MAP sensor pressure change is less than the expected value.

CONDITIONS FOR RUNNING THE DTC
^ Barometric pressure (BARO) is more than or equal to 75 kPa.
^ Engine coolant temperature is between 70°C and +110°C (158°F-230°F).
^ Intake air temperature is more than -8°C (+18°F).
^ Vehicle speed is at least 97 km/h (60 mph) for 7 minutes prior to deceleration.
^ The vehicle is allowed to decelerate with no accelerator or brake pedal input.
^ During deceleration the throttle valve angle is 0 degrees, and the engine is operating in Fuel Cutoff mode.

CONDITIONS FOR SETTING THE DTC
The difference in intake manifold pressure between when the EGR valve is OPEN, and when the EGR valve is CLOSED, is less than a specified value.

ACTION TAKEN WHEN THE DTC SETS
^ The PCM illuminates the malfunction indicator lamp (MIL) after 2 consecutive ignition cycles in which the diagnostic runs with the fault.
^ The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The PCM turns OFF the MIL after 3 consecutive trips without a fault.
^ The PCM clears a history DTC after 40 consecutive warm-up cycles without a fault.
^ You perform the scan tool Clear DTC Information function.

DIAGNOSTIC AIDS
A DTC P0401 is more likely to set during short trips on the highway. Operate the vehicle on the highway, with frequent closed throttle stops, in order to validate a DTC P0401.

Check for any of the following conditions:
^ An EGR valve that is stuck closed, stuck open, or binding.
^ The incorrect PCM can cause DTC P0401 to set. Check that the correct PCM is installed in the vehicle as required for proper emission certification.

A DTC P0401 sets when the change in MAP signal is less than the expected value during the operation of the EGR valve. Investigate any condition that can affect the accuracy of the MAP sensor readings:
^ Retarded ignition timing
^ Restricted exhaust system
^ Faulty MAP sensor
^ Restriction or a leak that affects the flow of exhaust gases through the EGR valve and into the intake air system.

If a DTC P0401 is intermittent, driving the vehicle under the conditions outlined in the Inspection/Maintenance (I/M) can verify whether the fault is present. Refer to Inspection/Maintenance (I/M) Exhaust Gas Recirculation (EGR) System Set Procedure. I/M EGR System Set Procedure

An intermittent malfunction may be caused by a fault in the EGR valve or MAP sensor electrical circuits. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions. Intermittent Conditions

If a DTC P0401 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC was first set.

EGR Valve Terminal (Pin) Identification:

Use the table in order to locate the correct terminals to test during diagnosis. The table layout corresponds to the pin location of the EGR valve electrical terminals.

TEST DESCRIPTION

Steps 1-5:

Steps 6-10:

Steps 11-20:

The number below refer to the step number in the diagnostic table.
1. The Diagnostic System Check-Computers and Controls Systems prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
3. This step checks for an EGR valve that is leaking, stuck open, or turned on at idle. Normal engine operating temperature is specified as 80°C (176°F) or above.