For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### 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 valve. Ignition 1 voltage is supplied directly to the EGR solenoid valve. The ECM controls the solenoid by grounding the control circuit. When the EGR solenoid valve 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

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### 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

1. Ignition ON, observe the DTC information with a scan tool. Verify that no other DTCs are set.

⇒ | If any other DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle for further diagnosis.

2. DTCs P0401 or P0402 should not set.
3. Command the throttle position from 0-100 percent with a scan tool. The throttle blade should respond to the scan tool commands.

⇒ | If the throttle body does not respond to the scan tool commands, refer to DTC P02E0 for further diagnosis.

4. Command the EGR solenoid valve from 0-100 percent with a scan tool. The EGR solenoid valve should respond to the scan tool commands.

⇒ | If the EGR solenoid valve does not respond to the scan tool commands, refer to DTC P0403 for further diagnosis.

5. 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

1. 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

2. Disconnect the vacuum source from the EGR solenoid valve.
3. Connect the J-23738-A Mity Vac 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.

4. Connect the vacuum source to the EGR solenoid valve. Connect the J-23738-A Mity Vac 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.

5. 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 position solenoid control circuit for greater than 5 Ω. If the circuits test normal, replace the EGR solenoid valve.

6. Connect the J 23738-A to the Q14 EGR valve vacuum hose. Apply 10 in Hg of vacuum to the Q14 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 Q14 EGR valve.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Exhaust Gas Recirculation Valve Solenoid Replacement

• | Exhaust Gas Recirculation Valve Replacement

• | Vacuum Pump Assembly Replacement