What the OBD-II code p0401 means

Fault code P0401 – a step-by-step guide to diagnosing and fixing it

The meaning of error code P0401 – Insufficient EGR Flow
P0401
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P0401: causes, symptoms and repairs

The meaning of fault code P0401

DTC P0401 is registered by the engine control unit (engine control module) when it determines that an insufficient amount of exhaust gas is being redirected through the car EGR valve. This recirculation process is supposed to lower the combustion temperatures and reduce harmful emissions. It is regulated based on the operating temperature and engine load.

Possible causes

  • Valve faults caused by a broken cable, a weak spring, or a damaged rubber membrane, preventing the device from regulating the flow of gases correctly.
  • An EGR valve that won’t open due to a low vacuum pressure. This may occur as a result of a leak in the vacuum lines, a solenoid malfunction, or a low pump output caused by a faulty drive belt.
  • Blockages obstructing the flow of exhaust gases into the air intake manifold. This often occurs when carbon deposits form in the passages of the system.
  • A jammed throttle valve caused by a build-up of carbon.
  • A broken pressure feedback (DPFE) or temperature sensor, generating false signals or failing to transmit accurate data.
Symptoms of the P0401 code

  • An increase in nitrogen oxide emissions (a failed emissions test)
  • Knocking or ignition pinging when accelerating
  • Increased fuel consumption
  • A rough idle
  • Activation of the check engine light
  • Surging or stalling
Recommended repairs

  • One of the first things that a qualified technician would do is check the registered trouble codes. You can do this yourself by connecting an OBD2 scanner to the vehicle’s onboard computer via the data link connector. They would then clear the codes and take the vehicle for a test drive to see if they reappear.
  • If there are vacuum leaks, restore the suction by replacing damaged vacuum lines, installing a new pump or tightening the clamps.
  • Clean the valves to remove deposits and contaminants. This can be done by using cleaning additives or by hand with a clean, lint-free cloth, a brush and special cleaning agent, such as a throttle body cleaner.
  • Inspect the wires and sensors for signs of damage or failure. Remove the temperature sensor and check whether carbon deposits have built up around the component causing problems. Check the voltage output of the DPFE device and compare the voltmeter or multimeter readings to the standard voltage range. Replace any defective electrical parts.
  • You can conduct a visual test for the EGR valve using a hand-held vacuum pump or using a vacuum gauge. If the component won’t open or stay open when the vacuum pump is working, you should install a new one.
Frequently Asked Questions (FAQ)

What does P0401 mean?


This code indicates that not enough exhaust gas is passing through the EGR to effectively lower the combustion temperature. This is often due to a faulty device, blocked air passages or vacuum leaks.

How can I get rid of this DTC?


It can be reset with a scan tool, but the system will need to be fixed if you want to clear this error permanently. Doing so will also help to prevent further damage from occurring.

Can I still drive my car, or is the P0401 code too serious?


It is possible to drive the vehicle as it should not pose an immediate risk to your safety or engine. However, this fault can lead to excessive pre-ignition, damaging the pistons and valves. There is also the risk of failing the emissions test as if the gases do not recirculate, the volume of toxic fumes increases.

Cars the fault code P0401 is most commonly found on

Fault code P0401 - Insufficient EGR Flow can occur with any car but is most often found on the following cars:

  • Audi: A4, A3, A6
  • VW: Golf, Passat, Crafter
  • Ford: Ranger, Mondeo, Focus

If you get the code P0401 on your car, make sure that the diagnostics are carried out correctly and the error is still relevant. Check for symptoms associated with the problem and explore options for resolving it.

What to do if the fault code p 0401 appears

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