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Home >> Chevy Truck >> 2010 >> Express 3500 V8-6.6L DSL Turbo >> Repair and Diagnosis >> A L L Diagnostic Trouble Codes ( DTC ) >> Testing and Inspection >> P Code Charts >> P0401 >> VIN 6

VIN 6




DTC P0401 or P0402

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (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). The ECM controls the EGR valve by suppling a 12-volt pulse width modulated (PWM) signal to the EGR solenoid high control circuit and a ground to the low control circuit. The ECM monitors the EGR flow efficiency when the EGR is active by comparing the desired Mass Air Flow (MAF) to the actual MAF. If the actual MAF is less than or greater than a calibrated threshold level the amount of detected EGR flow is out of range.

Conditions for Running the DTC

* DTCs P0101, P0102, P0103, P0403, P0405, P0406, P046C are not set.
* The engine is running.
* The engine coolant temperature (ECT) is greater than 60°C (140°F).
* The EGR valve is active.
* DTCs P0401 and P0402 run continuously when the above conditions are met.

Conditions for Setting the DTC

P0401

The ECM detects that the difference between the actual mass air flow and the desired mass air flow is less than a calibrated value for greater than 15 seconds when the EGR is active.

P0402

The ECM detects that the difference between the actual mass air flow and the desired mass air flow is greater than a calibrated value for greater than 15 seconds when the EGR is active.

Action Taken When the DTC Sets

P0401

DTC P0401 is a Type B DTC.

P0402
* DTC P0402 is a Type B DTC.
* Diesel particulate filter (DPF) regeneration is inhibited.
* The ECM commands the engine to operate in Reduced Engine Power mode.
* The message center displays Reduced Engine Power.

Conditions for Clearing the DTC

DTCs P0401 and P0402 are Type B DTCs.

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
* Aftermarket air filter

Reference Information
Schematic Reference

Engine Controls Schematics ([1][2]Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector End Views By Name)
DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Powertrain Diagnostic Trouble Code (DTC) Type Definitions)
Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information

Circuit/System Verification

Important: Occasionally, when using an EGR device control, Engine Reduced Power and Clean Exhaust Filter messages may occur after a short delay when commanding large EGR positions. The messages are a result of ECM protecting hardware during device control mode. No DTCs will be stored and the Diesel Particulate Filter does not need to be service cleaned. Exiting device control will restore normal function.


1. Verify if DTC P003A, P0101, P0403, P0405, P0406, P046C, P0698, or P0699 are not set.

• If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code (DTC) List - Vehicle).

2. Ignition ON, observe the Desired EGR Position and the EGR Position Sensor parameters. With a scan tool, command the EGR solenoid to 20 percent in 5 percent increments. The Desired EGR Position and the EGR Position Sensor parameters should respond and remain within 3 percent of each other with each command.

• If greater than the specified range or the EGR Position Sensor parameter does not respond and remains stationary, replace the EGR valve and gaskets.

3. Engine running at idle speed, perform the following:

* With a scan tool, command the EGR solenoid to 40 percent.
* Increase the engine speed to 2,500 RPM. The engine should run rough.

4. Operate the vehicle within the Conditions for Running the DTC to verify that 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

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

* Always replace the EGR valve or EGR cooler gaskets when removal or replacement of the components are necessary.

* Recording of Mass Air Flow parameter g/s are valid only if the Reduced Engine Power message is not present.


1. Engine running at idle, ECT parameter must be greater than 80°C (176°F). Perform the following:

1. Maintain engine speed at idle.
2. With a scan tool, command the EGR solenoid to 0 percent and record the Mass Air Flow g/s parameter.
3. With a scan tool, command the EGR solenoid to 40 percent while observing the actual EGR Position and the Mass Air Flow parameters. Record the Mass Air Flow g/s parameter. The difference between the Mass Air Flow g/s parameter at 0 percent EGR solenoid position and 40 percent EGR solenoid position should be greater than 15 g/s.

• If the Mass Air Flow parameter does not decrease by 15 g/s or more, inspect the EGR cooler and the EGR valve passages for a restriction.

2. Ignition OFF, inspect for the following:

* The exhaust system for leaks, restrictions, or for modification of the original equipment manufacture (OEM) part
* For a restriction in the air cleaner and the air intake ducts.
* For a restriction in the turbocharger charge air cooler (CAC) system.
* For a restriction in the intake manifold.

3. Test the air induction system for air leaks between the MAF sensor and the turbocharger. Perform the Induction System Smoke Test. Refer to Charge Air Cooler Diagnosis (Induction System Smoke Test) (Charge Air Cooler Diagnosis (Induction System Smoke Test)) Charge Air Cooler Diagnosis (Charge Air Cooler Air Leak Test) (Charge Air Cooler Diagnosis (Charge Air Cooler Air Leak Test)) Charge Air Cooler Diagnosis (Full System Air Leak Test) (Charge Air Cooler Diagnosis (Full System Air Leak Test)).
4. Test the charge air cooler system for leaks. Perform the Full System Air Leak Test. Refer to Charge Air Cooler Diagnosis (Induction System Smoke Test) (Charge Air Cooler Diagnosis (Induction System Smoke Test)) Charge Air Cooler Diagnosis (Charge Air Cooler Air Leak Test) (Charge Air Cooler Diagnosis (Charge Air Cooler Air Leak Test)) Charge Air Cooler Diagnosis (Full System Air Leak Test) (Charge Air Cooler Diagnosis (Full System Air Leak Test)).
5. If the air induction, charge air cooler (CAC), and mass air flow test normal, operate the vehicle within the Conditions for Running the DTC. If the DTC resets, perform the Component Testing.

Component Testing

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


1. Remove the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement (Exhaust Gas Recirculation Valve Replacement).
2. Inspect the EGR valve, the EGR cooler, the air inlet tube, and all of the EGR passages for the following conditions:

* A sticking, binding, or frozen EGR valve
* A leak or restriction in the EGR valve and EGR ports and passages
* Any coking, soot build up, debris, damage, that can cause the EGR valve to stick partially open or closed

• If any of the above conditions are found, replace the affected component and gaskets, as necessary.

Repair Instructions

* Exhaust Gas Recirculation Valve Replacement (Exhaust Gas Recirculation Valve Replacement)
* Exhaust Gas Recirculation Valve Cooler Replacement (Exhaust Gas Recirculation Valve Cooler Replacement)
* Diesel Particulate Filter (DPF) Regeneration Enable (Diesel Particulate Filter (DPF) Regeneration Enable)
* Intake Manifold Tube Replacement (LMM) (Intake Manifold Tube Replacement)

Repair Verification

1. Install any components or connectors that have been removed or replaced during diagnosis.
2. Perform any adjustment, programming, or setup procedures that are required when a component or module is removed or replaced.
3. Clear the DTCs.
4. Turn OFF the ignition for 60 seconds.
5. Duplicate the Conditions for Running the DTC and use the Freeze Frame/Failure Records, if applicable, in order to verify the DTC does not reset. If the DTC resets or another DTC is present, refer to Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code (DTC) List - Vehicle) and perform the appropriate diagnostic procedure.
6. Perform the Diesel Particulate Filter (DPF) Service Regeneration (Diesel Particulate Filter (DPF) Service Regeneration).

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