P0401 obd2 fault code represents exhaust gas recirculating (EGR) failure which comes about once the exhaust gas being supplied to the engine intake manifold combustion gas is obstructed. This EGR brings down engine combustion temperature and helps minimize pollution. Once employed in the engine, the egr system is made of: an egr valve which permits the exhaust gas to be fed to your combustion chamber, an actuator solenoid which moderates the vacuum going to the egr valve and finally the egr pressure sensor which evaluates the difference in pressure in the atmosphere and the vacuum circuit. The latter helps the smooth flow of exhaust gas at the egr valve during combustion.

As soon as this P0401 obd2 fault code comes along, it is commonly induced by the following factors:

The EGR valve is stuck and the pintle rod will not permit the flow of exhaust gas. During testing, determine the vacuum entering on top of egr valve and measure it at idle and high idle rpm. The vacuum reading must not be equal otherwise, the egr valve has failed.

The solenoid of the EGR can also break down mechanically but the basic problem is in the electrical wirings. It should be checked for voltage and resistance readings and compare them to the standard readings as suggested by the engine manufacturer. A shorted wiring tested by a voltmeter can also indicate a bad egr solenoid.

Actually, an EGR pressure sensor can break down depending on the make of the vehicle. On some popular engine makes, this is the common part to fail and can be checked by using the common fixes dabase as recommended by ATS. A quick way to test this is to check the sensor for leaks and proper connection by using a vacuum diagram.

Quick TIP on egr system

Having an engine vacuum diagram can help you identify all the egr system components. It will also show the connections of the egr system incase it was tampered with before you did the repair.

Usually, when the P0401 obd2 fault code occurs, it’s like restricting the air going to the engine manifold which could make the combustion mixture rich causing misfiring. On the other hand, if the egr is stuck open, it will cause the fuel mixture lean because of additional air being supplied by the egr system.

A better way to check this P0401 obd2 fault code is to test for vacuum leaks on all egr components including the integrity of the vacuum passages and wiring circuits applied to it. It also recommended to reset the fault code and see if the code re-emerges so that each of the major parts mentioned above are tested one by one.

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