Diagnostic Instructions
DTC Descriptors
DTC P0401: Exhaust Gas Recirculation (EGR) Flow Insufficient
DTC P0402: Exhaust Gas Recirculation (EGR) Flow Excessive
Circuit/System Description
The exhaust gas recirculation (EGR) valve is controlled by the engine control module (ECM) through the EGR solenoid. Ignition 1 voltage is supplied directly to the EGR valve solenoid. The ECM controls the solenoid by grounding the control circuit.
When the EGR solenoid is commanded ON, vacuum from the vacuum pump is applied to the EGR valve.
Conditions for Running the DTC
• | The ignition is ON, or the engine is running. |
• | The DTCs run continuously when the above conditions are met. |
Conditions for Setting the DTC
P0401
The ECM detects the EGR flow is below a calibrated amount when the EGR is commanded ON.
P0402
The ECM detects the EGR flow is above a calibrated amount when the EGR is commanded OFF.
Action Taken When the DTC Sets
DTCs P0401, and P0402 are Type B DTCs.
Conditions for Clearing the DTC
DTCs P0401, and P0402 are Type B DTCs.
Reference Information
Schematic Reference
Engine Controls Schematics
Connector End View Reference
Component Connector End Views
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
Special Tools
J 23738-A
Mity Vac
Circuit/System Verification
- Ignition ON, observe the DTC information with a scan tool. Verify that no other DTCs are set.
- DTCs P0401 or P0402 should not set.
- Command the throttle blade from 0-100 percent with a scan tool. The throttle blade should respond to the scan tool commands.
- Command the EGR solenoid valve from 0-100 percent with a scan tool. The EGR solenoid should respond to the scan tool commands.
- Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
Circuit/System Testing
- Ignition OFF, inspect for the following:
• | Intake system/charge air hoses for leaks/restrictions |
• | Exhaust system/turbo charger for leaks/restrictions |
• | Vacuum supply system for leaks or blockage |
• | Air filter for restrictions |
- Disconnect the vacuum source from the EGR solenoid.
- Connect the
J 23738-A
to the EGR solenoid vacuum supply hose. Engine running, verify the vacuum is greater than 20 in Hg.
⇒ | If less than the specified range, inspect the vacuum supply hose and filter for a leak or restriction. If the supply hose is normal, replace the vacuum pump. |
- Connect the vacuum source to the EGR solenoid valve. Connect the
J 23738-A
to the EGR vacuum port on the EGR solenoid valve. Engine running, command the EGR solenoid valve to 5 percent with
a scan tool. Verify the vacuum is at 0 in Hg.
⇒ | If greater than the specified range, replace the EGR solenoid valve. |
- Command the EGR solenoid valve to 100 percent with a scan tool. Verify the vacuum is greater than 20 in Hg.
⇒ | If less than the specified range, test the ignition 1 voltage circuit and the EGR solenoid control circuit for greater than 5 ohms of resistance. If the circuits test normal, replace the EGR solenoid valve. |
- Connect the
J 23738-A
to the EGR valve vacuum hose. Apply 10 in Hg of vacuum to the EGR valve. Verify the EGR valve operation.
⇒ | If the EGR valve does not operate, inspect the vacuum hose for leaks or restrictions. If no leaks or restrictions are found, replace the EGR valve. |
Repair Instructions
Perform the
Diagnostic Repair Verification after completing the diagnostic procedure.