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 solenoid 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 set.
* The engine speed is between 500-950 RPM.
* The calculated fuel rate is between 1-15 mm(3)
* 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 mm(3).
* 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 (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
Note: 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. 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 parameters should respond and remain within 3 % throughout the commanded range.
2. Engine running command the EGR Valve to 40 % with a scan tool, then increase the engine speed to 2,500 RPM. The engine should run rough.
3. 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 solenoid to 0 % and record the MAF Sensor g/s parameter.
3. Command the EGR solenoid to 40 % with a scan tool while observing the EGR Position Sensor and the MAF Sensor g/s parameters. Record the MAF Sensor parameter. The difference between the MAF Sensor parameter at 0 % EGR solenoid position and 40 % EGR solenoid position should be greater than 15 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 passages for a restriction. If a condition is found, repair or replace the affected component as necessary.
2. Ignition OFF, inspect for the following:
* The exhaust system for leaks, restrictions, or for modification of the original equipment manufacture (OEM) part
* A restriction in the air cleaner and the air intake ducts
* A restriction in the turbocharger charge air cooler system
* A restriction 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 Charge Air Cooler Diagnosis.
4. Test the charge air cooler system for leaks. Perform the Full System Air Leak Test. Refer to Charge Air Cooler Diagnosis Charge Air Cooler Diagnosis.
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 diagnostic procedure.
* Exhaust Gas Recirculation Valve Replacement (Exhaust Gas Recirculation Valve Replacement)
* Control Module References (Programming and Relearning)for ECM replacement, programming, and setup