| Table 1: | EGR Valve Terminal (Pin) Identification |
Circuit Description
The 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 suspects that the EGR valve flow is incorrect when the monitored MAP sensor pressure change is too small.
Conditions for Running the DTC
| • | DTC P0107 and DTC P0108 are not set. |
| • | Barometric pressure (BARO) is more than or equal to 75 kPa. |
| • | Engine coolant temperature is between 70-110°C (158-230°F). |
| • | Intake air temperature is between -14 to +70°C (7-158°F). |
| • | Vehicle speed is between 50-65 km/h (30-40 mph). |
| • | Engine speed is between 2,000-3,000 RPM for 3 minutes. |
| • | Throttle valve opening remains constant. |
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 active. |
| • | 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 MIL turns OFF after 3 consecutively passing trips without a fault present. |
| • | A history DTC clears after 40 consecutive warm-up cycles without a fault. |
| • | Perform the scan tool Clear DTC Information function in order to clear the DTC. |
Diagnostic Aids
Check for 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 and software calibrations are installed in the vehicle as required for proper emission certification. |
A DTC P0401 may set when the expected change in MAP 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 leak that affects the flow of exhaust gases through the EGR valve and into the intake air system. |
| • | The DTC P0401 diagnostic test is more likely to run in city driving. Avoid long road tests at highway speeds when attempting to validate a DTC P0401. |
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 .
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.
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 .
Use the following 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.
Connector Lock Tab | ||
Pin 3 | Pin 2 | Pin 1 |
Pin 6 | Pin 5 | Pin 4 |
Test Description
The number below refer to the step number in the diagnostic table.
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The Diagnostic System Check-Engine Controls 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.
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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).
-
This step checks the integrity of the EGR control circuits. The EGR valve control circuits can be tested at the PCM connector. 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).
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This step checks the ignition positive voltage supply to the EGR coils.
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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.
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This step checks for restrictions that can affect the flow of exhaust gas into the intake collector. The EGR valve may flow enough to affect idle quality, but not flow enough to reach calibrated MAP values when the DTC P0401 diagnostic runs.
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This step checks whether the malfunction that caused the DTC P0401 is still present. 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.
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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.
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||||||
Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | ||||||||||
2 | Is a DTC P0403 also set? | -- | Go to DTC P0403 | Go to Step 3 | ||||||||
Does the engine run rough or stall? | -- | Go to Step 9 | Go to Step 4 | |||||||||
Does the EGR valve pass both tests? | 5 % | Go to Step 5 | Go to Step 6 | |||||||||
5 |
Does the EGR valve pass both tests? | 5 % | Go to Step 7 | Go to Step 6 | ||||||||
6 |
Does the EGR valve pass all resistance tests? | 20-24 ohms at 20°C (68°F) | Go to Step 8 | Go to Step 15 | ||||||||
7 |
Did you find and correct a condition? | -- | Go to Step 18 | Go to Step 15 | ||||||||
Did the test lamp illuminate for both circuits? | -- | Go to Step 14 | Go to Step 13 | |||||||||
Did you find and correct a condition? | -- | Go to Step 18 | Go to Step 10 | |||||||||
Did you find and correct the condition? | -- | Go to Step 18 | Go to Step 11 | |||||||||
11 |
Did you find and correct a condition? | -- | Go to Step 18 | Go to Step 12 | ||||||||
Is a DTC P0401 set? | -- | Go to Step 15 | Go to Diagnostic Aids | |||||||||
13 | Repair the ignition positive voltage supply to the EGR valve. Refer to Wiring Repairs in Wiring Systems. Did you complete the action? | -- | Go to Step 18 | -- | ||||||||
14 |
Did you find and correct a condition? | -- | Go to Step 18 | Go to Step 16 | ||||||||
15 | Replace the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement . Did you complete the replacement? | -- | Go to Step 18 | -- | ||||||||
16 |
Did you find and correct the condition? | -- | Go to Step 18 | Go to Step 17 | ||||||||
17 |
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 18 | -- | ||||||||
Does the DTC run and pass? | -- | Go to Step 19 | Go to Step 2 | |||||||||
19 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||||
