Rick's Free Auto Repair Advice

P0401 code — What it means and how to fix it

Learn what a P0401 code for EGR means and how to fix the problem

This image shows an electrically controlled EGR valve that can cause a P0401 code

This is a typical EGR valve with a valve position sensor situated on the top of the valve. It’s the sensor that usually goes bad. But you usually can’t buy just the sensor

A P0401 code is defined as Exhaust Gas Recirculation Flow Insufficient Detected; meaning that the commanded amount of EGR flow doesn’t match the actual EGR flow.

The EGR system is responsible for diverting a certain amount of exhaust gas to the intake manifold air to reduce combustion chamber temperatures and reduce NOx formation. See this more in-depth post for more information on the EGR system and why it’s needed.

The most common causes of a P0401 code

• Clogged EGR passages in the intake
• Carbon buildup on the EGR valve seat or pintle that prevents full exhaust gas airflow.
• Faulty EGR solenoid or vacuum actuator that prevents the EGR from opening fully.
• Faulty vacuum solenoid to vacuum-operated EGR valves

• Defective EGR Valve Position Sensor — The EGR position sensor reports how far open the valve is. The computer compares the commanded opening to the data from the sensor and sets a code if the sensor opening value doesn’t match the commanded opening. In many cases, it’s just a failed sensor that sits on top of the EGR valve. This is especially common on Chrysler vehicles.

• Defective EGR Valve Position Sensor connector and wiring — Since the EGR valve is recirculating very hot exhaust gasses, the heat may have damaged the electrical connector. So check that first, before replacing the valve.

• Defective DPFE (Differential Pressure Feedback EGR) Sensor and/or Wiring — This is a common failure on Ford products that don’t use a position sensor and instead use a Differential Pressure Feedback Sensor. Ford DPFE sensors have a high failure rate.

The most probable causes of the P0401 code are related directly to the EGR valve itself. It could be faulty or there might be a bad connection. Here are some of the most common causes of the P0401 code:

Here are some steps to diagnose and fix the P0401 code

Remove the EGR valve and check for carbon buildup in the valve, seat, or pintle

Check for a blocked EGR passage in the intake manifold or exhaust supply tubes.

Check the operation of a vacuum-operated or electrically-operated EGR valve.

Connect an OBD-II scanner to the vehicle’s diagnostic connector and read all stored data and error codes.
Clear the error codes from the computer memory and test-drive the vehicle to see if code P0401 appears again.
Inspect the EGR valve position sensor and wiring for damage.
Inspect the differential pressure feedback electronic (DPFE) sensor and wiring for damage.
Check the wiring and connectors for damage or looseness.
Replace the EGR valve position sensor if it is faulty.
Replace the differential pressure feedback electronic (DPFE) sensor if it malfunctions.
Repair or replace any damaged or loose wiring or connectors.
If the problem persists, the ECM may be faulty and require replacement.
© 2012 Rick Muscoplat

Posted on by Rick Muscoplat

Custom Wordpress Website created by Wizzy Wig Web Design, Minneapolis MN