P0401

DTC P0401: Exhaust Gas Recirculation (EGR) Flow Insufficient

Circuit Description
An Exhaust Gas Recirculation (EGR) system is used to lower Nitrogen Oxide (NOx) emission levels caused by high combustion temperatures. It accomplishes this by feeding small amounts of exhaust gases back into the combustion chamber. When the air/fuel mixture is diluted with the exhaust gases, combustion temperatures are reduced.

An electric EGR valve is used on this system. The electric EGR valve is designed to accurately supply exhaust gases to the engine without the use of intake manifold vacuum. The valve controls exhaust flow going into the intake manifold from the exhaust manifold through an orifice with an Engine Control Module (ECM) controlled pintle. The ECM controls the pintle position using inputs from the Throttle Position (TP) and Manifold Absolute Pressure (MAP) sensors. The ECM then commands the EGR valve to operate when necessary by controlling an ignition signal through the ECM. This can be monitored on a scan tool as the Desired EGR Position.

The ECM monitors the results of its command through a feedback signal. By sending a 5 volt reference and a ground to the EGR valve, a voltage signal representing the EGR valve pintle position is sent to the ECM. This feedback signal can also be monitored on a scan tool and is the actual position of the EGR pintle. The Actual EGR Position should always be near the commanded or Desired EGR Position.

This diagnostic will determine if there is a reduction in EGR flow.

Conditions for Setting the DTC
- No EGR fault exists.
- Engine speed is between 1,376 and 3,104 rpm.
- MAP is greater than 150 kPa.
- Throttle position is between 2.341 degrees and 13.122 degrees.
- Battery voltage is between 10.968 and 15.640 V.
- Air temperature at the throttle body is -15 degrees C (5 degrees F) or greater.
- Ambient pressure is 740.04 kPa or greater.
- Intake absolute pressure difference between closed and 20% throttle position is less than 2.3 kPa.
- Intake absolute pressure difference between closed and 50% throttle position is less than 2.3 kPa.

Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate.
- The ECM will record operating conditions at the time the diagnostic fails. The information will be stored in the Freeze Frame data, and Failure Records buffers.
- A history Diagnostic Trouble Code DTC is stored.

Conditions for Clearing the MIL/DTC
- The MIL will turn OFF at the end of 3 consecutive validation cycles in which the diagnostic runs without a fault.
- A history DTC will clear after 40 warm up cycles without a fault.
- DTC(s) can be cleared by using the scan tool.

Test Description
The numbers below refer to the step numbers on the diagnostic table.
3. MAP sensor faults must be diagnosed first. A skewed MAP sensor reading could cause this DTC to set.
7. An engine mechanical condition may cause the engine to operate poorly, which could cause a low vacuum condition.

Step 1 - 10:

DTC Troubleshooting