P0401

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 supplying a 12-volt pulse width modulated signal to the EGR Valve low control circuit and 12 volts to the high control circuit. The ECM monitors the EGR flow performance 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

P0401

* DTC P0045, P0047, P0048, P006E, P006F, P007C, P007D, P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P02E0, P02E7, P02E8, P02E9, P02EB, P0403, P0405, P0406, P0489, P0490, P122C, P122E, P122F, P1407, P140D, P140E, P140F, P1411, P1412, P1413, P1414, P16A0, P16A1, P16A2, P2228, P2229, P2263, P2453, P245A, P245C, P245D, P2493, P2494, P2495, P2564, P2565, P2598, or P2599 is not active.

* The engine speed is between 500-950 RPM.

* The calculated fuel rate is between 1-15 mm3

* The ambient air temperature is greater than -7°C (19.4°F).

* The engine coolant temperature is greater than 70°C (158°F).

* The Barometric Pressure is greater than 74.8 kPa (10.9 psi).

* The system is not in Diesel Particulate Filter (DPF) regeneration.

* The EGR valve position is greater than 5 %.

* The throttle valve position is less than 5 %.

* The DTC runs continuously when the above conditions are met.

P0402

* DTC P0045, P0047, P0048, P006E, P006F, P007C, P007D, P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P02E0, P02E7, P02E8, P02E9, P02EB, P0403, P0405, P0406, P0489, P0490, P122C, P122E, P122F, P1407, P140D, P140E, P140F, P1411, P1412, P1413, P1414, P16A0, P16A1, P16A2, P2228, P2229, P2263, P2453, P245A, P245C, P245D, P2493, P2494, P2495, P2564, P2565, P2598, or P2599 is not set.

* The engine speed is between 1,200-1,400 RPM.

* The calculated fuel rate is greater than 40 mm3.

* The ambient air temperature is greater than -7°C (19.4°F).

* The Barometric Pressure is greater than 74.8 kPa (10.9 psi).

* The system is not in Diesel Particulate Filter (DPF) regeneration.

* The EGR valve is active.

* The DTC runs 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 10 s.

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 10 s.

Action Taken When the DTC Sets

DTC P0401 and P0402 are Type B DTCs.

Conditions for Clearing the DTC

DTC 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 sensor

* 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 1-2 Shift Solenoid (SS) Valve (M30)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References Control Module References for scan tool information

Circuit/System Verification

1. Ignition ON, observe the scan tool DTC information. Verify DTC P0403 is not set.

• If a DTC is set, refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle.

Note: 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.

2. Ignition ON, observe the scan tool Desired EGR Position and the EGR Position Sensor parameters. Command the EGR Valve to 40 % with a scan tool. The readings should remain within 3 % throughout the commanded range.

3. Command the EGR Valve to 40 % with a scan tool while observing the EGR Position Sensor and the MAF Sensor g/s parameters. Record the MAF Sensor reading. The difference between the MAF Sensor reading at 0 % EGR Valve position and 40 % EGR Valve position should be greater than 13.5 g/s.

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

Note:

* 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 is necessary.

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

1. Engine running, perform the following:

1. Maintain engine speed at idle.

2. With a scan tool, command the EGR Valve to 0 % and record the MAF Sensor g/s parameter.

3. Command the EGR Valve to 40 % with a scan tool while observing the EGR Position Sensor and the MAF Sensor g/s parameters. Record the MAF Sensor reading. The difference between the MAF Sensor reading at 0 % EGR Valve position and 40 % EGR Valve position should be greater than 19 g/s.

• If the MAF Sensor parameter is not within the specified range, inspect the EGR cooler, EGR cooler bypass valve, (if equipped), and the EGR valve and passages for a restriction. If a condition is found, repair or replace the affected component as necessary.

2. Ignition OFF, verify the conditions listed below do not exist:

* Exhaust system leaks, restrictions, or for modification of the original equipment manufacturer (OEM) part

* Restrictions in the air cleaner and the air intake ducts

* Restrictions or damage to the turbocharger. Refer to Turbocharger Cleaning and Inspection Turbocharger Cleaning and Inspection

* Restrictions in the charge air cooler

* Restrictions in the intake manifold

• If a condition is found, repair or replace the affected component as necessary.

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 (Full System Air Leak Test) Charge Air Cooler Diagnosis (Full System Air Leak Test)Charge Air Cooler Diagnosis (Induction System Smoke Test) Charge Air Cooler Diagnosis (Induction System Smoke Test).

4. Test the charge air cooler system for leaks. Perform the Full System Air Leak Test. Refer to Charge Air Cooler Diagnosis (Full System Air Leak Test) Charge Air Cooler Diagnosis (Full System Air Leak Test)Charge Air Cooler Diagnosis (Induction System Smoke Test) Charge Air Cooler Diagnosis (Induction System Smoke Test).

5. If the exhaust, air induction, charge air cooler and mass air flow systems test normal, Test or replace the Q14 EGR Valve.

Component Testing

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

1. Ignition OFF, remove the Q14 EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement Exhaust Gas Recirculation Valve Replacement.

2. Inspect the Q14 EGR valve 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 or damage that can cause the EGR valve to stick partially open or closed

• If a condition is found, replace the Q14 EGR Valve.

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the repair.

* Exhaust Gas Recirculation Valve Replacement Exhaust Gas Recirculation Valve Replacement

* Control Module References Control Module References for ECM replacement, programming, and setup