P0401 EGR Insufficient Flow

P0401 - Insufficient Exhaust Gas Recirculation Flow

The Exhaust Gas Recirculation (EGR) valve recirculates a small amount of exhaust gases back to the engine's combustion chambers to reduce the amount of oxygen and increase water vapor, thereby reducing the formation of smog-forming nitrogen oxides (NOx). When DTC P0401 is set, the exhaust gases are re-entering the combustion chamber at the wrong time or in the wrong amounts, which does not reduce the oxygen level sufficiently to prevent the increase in NOx. This is likely due to a faulty or clogged EGR valve or carbon buildup in the intake manifold or on the EGR temperature sensor.

Technical description

• Insufficient Exhaust Gas Recirculation (EGR) Flow
• "Insufficient EGR flow detected."

What the P0401 code means

• Severity of the problem: MODERATE. Continued driving with this code may cause internal engine damage.
• Urgent Repair: Fix this code as soon as possible to avoid internal engine damage.
• Diagnostics: Code P0401 can cause excessive internal engine ignition and damage to pistons and valves before ignition.

This diagnostic trouble code (DTC) is a generic transmission code, which means it applies to OBD-II equipped vehicles. Although general, specific repair steps may vary depending on the make/model. EGR stands for Exhaust Gas Recirculation. It is part of the vehicle exhaust system and is used to reduce combustion temperature and pressure to control nitrogen oxides. Typically, the EGR system consists of three parts: the EGR valve, the actuator solenoid, and the EGR differential pressure sensor (DPFE). These things work together to provide the correct amount of recirculation depending on engine temperature, load, etc. Code P0401 means that the OBD has detected insufficient EGR. P0401 is a generic OBD-II code indicating that the Engine Control Module (ECM) has detected that the Engine Exhaust Gas Recirculation (EGR) valve is not allowing enough recirculated exhaust gases to pass through when commanded to open the flow of gases into the intake manifold.

Symptoms for error code P0401

You may notice handling problems such as ringing (aka pre-ignition knock) when the engine is under load or the vehicle is moving at higher speeds. There may be other symptoms as well.

• The Check Engine light will illuminate on the instrument panel.
• Slower and more difficult acceleration.
• Emission test failed.
• Driving problems
• Loss of power
• Ignition ping.

Possible Causes of Code P0401

The P0401 code most likely means that one or more of the following events have occurred:

• The DPFE (Differential Pressure Feedback EGR) sensor is defective and needs to be replaced.
• A clogged exhaust gas recirculation pipe is most likely a carbon build-up.
• Exhaust gas recirculation valve defective
• The exhaust gas recirculation valve may not open due to lack of vacuum.

EGR flow failure can be caused by a clogged EGR valve or EGR tube. Before replacing any parts, try cleaning the EGR valve, hose and passages.

Possible solutions to troubleshoot the P0401 code

When fixing this code, it's quite common for people to simply replace the EGR valve just to fix the OBD code. The EGR valve is not always the root cause.

• Use a vacuum pump and open the EGR valve while monitoring the engine speed and DPFE voltage. There should be a noticeable difference in rpm with an open EGR system.
• Clean the exhaust gas recirculation valve and / or pipe to remove deposits.
• Check voltage at DPFE, compare with specified values ​​(see MR for your specific model)
• Replace DPFE sensor (quality / OEM)
• Replace the exhaust gas recirculation valve.

Associated EGR Codes: P0400, P0402, P0403, P0404, P0405, P0406, P0407, P0408, P0409

How to Fix P0401 Engine Code in 3 Minutes [2 DIY Methods / Only $4.13]

How does a mechanic diagnose a P0401 code?

1. Scans codes and documents freeze frame data to confirm problem.
2. Clears engine and ETC codes and road tests the vehicle to see if the codes return.
3. Visually inspects vacuum hoses, wiring, and connections to EGR valve and control solenoid, and EGR temperature sensor.
4. Disconnects and checks if the EGR valve is supplying sufficient engine vacuum to the valve when the control solenoid opens under light to medium acceleration.
5. Checks for EGR temperature sensor changes and engine shutdown when EGR opens.
6. Removes the EGR valve and temperature sensor to check for excessive carbon deposits or partial blockage in the EGR pipes from the valve to the intake manifold.

Common Mistakes When Diagnosing Code P0401

• Lack of checking and cleaning the EGR channels when replacing a faulty EGR valve.
• Diagnosing a cause in a good EGR valve when the EGR temperature sensor has excessive carbon buildup causing the DTC.
• Unable to test if the EGR control solenoid will hold vacuum before replacing the EGR valve.

How serious is the P0401 code?

A faulty EGR valve can result in excessive engine pre-ignition, which can cause internal damage to the engine piston and valves. An illuminated Check Engine Light will cause the vehicle to fail an emissions test due to excessive NOx gases.

What repairs can fix code P0401?

• Replacing a leaking or clogged EGR valve;
• Replacing a broken vacuum line to the EGR valve or control solenoid;
• Replacing the EGR temperature sensor or cleaning it of soot to repair it if it does not register a sufficient change in temperature;
• Cleaning carbon deposits from the exhaust gas recirculation pipes to the intake manifold to eliminate blockages.

Additional comments to consider regarding code P0401

Code P0401 occurs when the EGR temperature sensor does not see enough change in temperature when the EGR is commanded to open. These sensors tend to accumulate a lot of carbon, which causes them to become insensitive to heat from EGR gases. P0401 is an Exhaust Gas Recirculation Flow Diagnostic Diagnostic Trouble Code (DTC). This can happen for several reasons and it is up to the mechanic to diagnose the specific cause of this code being triggered in your situation.

P0401 Brand specific information

• P0401 ACURA Exhaust Gas Recirculation Insufficient Flow
• P0401 AUDI Insufficient Exhaust Gas Recirculation Flow Detected
• P0401 BUICK Exhaust Gas Recirculation Flow Insufficient
• P0401 CADILLAC Exhaust Gas Recirculation Flow Insufficient
• P0401 CHEVROLET Exhaust Gas Recirculation Flow Insufficient
• CHRYSLER P0401 Vehicle EGR System Performance
• P0401 DODGE Exhaust Gas Recirculation System Performance
• P0401 FORD Exhaust Gas Recirculation Insufficient Flow Detected
• P0401 GMC Exhaust Gas Recirculation Flow Insufficient
• P0401 HONDA Exhaust Gas Recirculation Insufficient Flow
• P0401 ISUZU Insufficient Exhaust Gas Recirculation Flow Detected
• P0401 JEEP Exhaust Gas Recirculation System Performance
• P0401 KIA Insufficient Exhaust Gas Recirculation Flow Detected
• P0401 LEXUS Exhaust Gas Recirculation Insufficient Detection
• P0401 LINCOLN EGR flow not detected
• P0401 MAZDA EGR flow not detected
• P0401 MERCEDES-BENZ Exhaust Gas Recirculation Flow Not Detected
• P0401 MERCURY EGR flow not detected
• P0401 MITSUBISHI EGR flow not detected
• P0401 PONTIAC Exhaust Gas Recirculation Flow Insufficient
• P0401 SATURN Exhaust Gas Recirculation Flow Insufficient
• P0401 SCION Insufficient Exhaust Gas Recirculation Flow Detected
• P0401 SUZUKI Exhaust Gas Recirculation Flow Not Detected
• P0401 TOYOTA EGR flow not detected
• P0401 VOLKSWAGEN Insufficient Exhaust Gas Recirculation Flow Detected

How much does it cost to fix code P0401?

The P0401 code can be caused by anything from a clogged EGR valve to a faulty EGR temperature sensor to an engine vacuum leak. It is impossible to give an accurate assessment without correctly diagnosing the problem. If you take your vehicle to a shop for diagnostics, most shops will start with an hour of "diagnostic time" (the time it takes to diagnostics your specific problem). Depending on the rate per hour in the workshop, this usually costs between $30 and $150. Many, if not most, shops will charge this diagnostic fee on any necessary repair if you ask them to do the repair for you. The technician will then be able to give you an accurate repair estimate to fix the P0401 code.

Possible repair costs for P0401

Error code P0401 may require one or more of the following repairs to resolve the underlying problem. For each possible repair, the estimated cost of the repair includes the cost of the relevant parts and the cost of the labor required to complete the repair.

• EGR valve: $200 to $413
• Vacuum leak: $50 to $125.