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 Descriptor

DTC P0401 00: Exhaust Gas Recirculation (EGR) Flow Insufficient
DTC P0402 00: 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 valve. A reference voltage is supplied to the EGR valve. The ECM controls the valve by grounding the control circuit.

### 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

### 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 plate from 0-100% with a scan tool. The throttle plate should respond to the scan tool commands.

⇒ | If the throttle body does not respond to the scan tool commands, refer to DTC P2100, P2102, P2103 for further diagnosis.

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

⇒ | If the EGR solenoid does not respond to the scan tool commands, refer to DTC P0403, P0489, or P0490 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

• | Air filter for restrictions

2. Engine running at idle, command the EGR Valve ON with a scan tool. Verify that the mass air flow (MAF) Sensor parameter is less than16 kg/h

⇒ | If the parameter is greater than the specified value, replace the Q14 Exhaust Gas Recirculation (EGR) Valve.

3. Command the EGR Valve OFF with a scan tool. Verify that the MAF Sensor parameter is greater than 25 kg/h

⇒ | If the parameter is less than the specified value, replace the Q14 Exhaust Gas Recirculation (EGR) Valve.

4. Verify the DTC does not reset.

⇒ | If the DTC is set, replace the K20 Engine Control Module (ECM).

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Exhaust Gas Recirculation Valve Replacement

• | Control Module References for engine control module replacement, setup, and programming