P0401
CIRCUIT DESCRIPTIONThe DTC P0401 Exhaust Gas Recirculation (EGR) Flow Insufficient 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) section 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.
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 1-4:
Steps 5-6:
Steps 7-8:
Steps 9-12:
Steps 13-17:
Steps 18-20:
The number below refer to the step number in the diagnostic table.
1. The Diagnostic System Check-Computers and Control 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.
4. This step checks the operation of the EGR valve. The duty cycle output control of the EGR is disabled by the PCM when any DTCs are stored and when the engine temperature is less than 80°C (176°F).
8. This step checks for a physically stuck EGR valve or plugged EGR passages.
9. This step checks the ignition positive voltage supply to the EGR coils.
10. This step checks for proper manifold absolute pressure (MAP) sensor operation. The diagnostic for a DTC P0401 depends on MAP sensor output in order to monitor EGR valve performance.
11. Fault not present indicates the condition that caused DTC P0401 to set is intermittent and not currently present. If no other DTCs are stored, refer to diagnostic aids for additional information on diagnosing an intermittent DTC P0401.
12. This step determines whether an electrical fault is the cause of the EGR valve staying open. A grounded EGR valve control circuit can cause the EGR valve to be open all the time.
14. This step checks for an EGR valve control circuit that is shorted to ground. If the circuit wiring is OK, a faulty PCM with an internally shorted circuit can cause the EGR valve to be open.
19. Clearing the DTCs by removing the DOME fuse also clears the PCM long term memory. Using the scan tool to clear DTCs leaves the long term memory active. DTC emitting diagnostics may not run to completion as expected unless the long term memory is cleared. Removal of the DOME fuse also clears the time display of the radio. The DTC P0401 diagnostic can be monitored on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0401 appears in the Not Ran Since Code Cleared list, the DTC P0401 diagnostic has not yet run. When the DTC P0401 does not appear in the Not Ran Since Code Cleared list, the DTC P0401 diagnostic has run. If the MIL is NOT illuminated, and there is no Pending DTC Status in DTC Information, the DTC P0401 diagnostic has passed. The DTCs MUST be cleared in order to view the Current Status of the Not Ran Since Code Cleared list. DO NOT forget that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for Current or Pending status, in order to determine the outcome of the diagnostic test involved.