P0401

DTC P0401 or P0402

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 engine control module (ECM) tests the exhaust gas recirculation (EGR) flow when the EGR is in operation. EGR desired flow is compared to EGR actual flow. If EGR flow is lower or higher than expected DTC P0401 or P0402 will set.

Conditions for Running the DTC

* DTCs P0101, P0102, P0103, P0403, P0405, P0406, P046C are not set.
* The engine is running
* The EGR valve is actively being controlled.
* DTCs P0401 and P0402 run continuously when the above conditions are met.

Conditions for Setting the DTC

P0401

The ECM calculated air flow deviation based on the MAF sensor input during EGR operation indicates insufficient EGR flow for 15 seconds.

P0402

The ECM calculated air flow deviation based on the MAF sensor input during EGR operation indicates excessive EGR flow for 15 seconds.

Action Taken When the DTC Sets

DTCs P0401 is a Type B DTC.

DTC P0402 is a Type A DTC.

Conditions for Clearing the DTC

DTCs P0401 is a Type B DTC.

DTC P0402 is a Type A DTC.

Diagnostic Aids

Inspect for the following conditions that may cause this DTC to set:

* Contamination on the MAF sensor element
* Restriction before or after the MAF
* Skewed MAF sensor

Circuit/System Verification

1. If DTC P0101, P0403, P0405, P0406, P046C, P0698, or P0699 are set, diagnose these DTCs.
2. Using the output controls on the scan tool command the EGR solenoid to 10 percent.

• If the actual EGR position remains stationary, replace the EGR valve.

3. Inspect the exhaust system for leaks, restrictions, or for modification of the original equipment manufacture (OEM) part.
4. Visually inspect for leaks between the MAF sensor and the turbocharger.
5. Visually inspect for a restriction in the air cleaner or the air intake ducts.
6. Visually inspect for a restriction in the turbocharger charge air cooler.
7. Visually inspect for a restriction in the intake manifold.
8. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame Records data.

Circuit/System Testing

Important: Perform the Circuit System Verification before proceeding with Circuit/System Testing.

Inspect the charge air cooler for leaks.

If no problem is found, perform the component testing.

Component Testing

Important: Perform the Circuit/System Verification before proceeding with the Component Testing.

1. Using the output controls on the scan tool command the EGR solenoid to 10 percent.

• If the actual EGR position remains stationary, replace the EGR valve.

2. Spray the EGR valve gaskets and EGR cooler gaskets with a soap solution. Start the engine. Command the turbocharger vane position control solenoid ON to 100 percent and inspect for leaks around the EGR valve gaskets.

• If a leak is found replace the EGR valve gasket.

3. Remove the EGR valve.

• If the EGR valve is sticking, or is damaged, replace the EGR valve.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

Exhaust Gas Recirculation Valve Replacement