Car Repair

Emission Repair: EGR System

Vehicle On Board Diagnostic System trouble code P0401 is frequently misunderstood. The code description reads as follows: EGR insufficient flow. You must first understand that including a component name (EGR) in the code description does NOT constitute its failure. Code setting parameters are thus: Insufficient EGR flow has been determined by one or more sensors (during a two trip drive cycle) when predetermined conditions were met and insufficient changes in intake manifold temperature and/or pressure were not detected. This condition triggered the Powertrain Control Module (PCM) causing it to set a malfunction code and illuminate the Service Engine Soon Indicator. Insufficient flow may be due to a number of factors.

Here are the most likely causes:

* Carbon clogged tubes or passages between the EGR and intake manifold.
* Disconnected of burned EGR hoses between EGR and intake manifold.
* Clogged or broken vacuum line between throttle body and EGR valve or EGR solenoid.
* Faulty EGR temperature sensor.
* Faulty Delta Process Flow EGR sensor (DPFE).
* Faulty EGR position sensor.
* Faulty manifold air pressure sensor.
* Faulty EGR actuator solenoid.
* Faulty EGR valve.


The purpose of the EGR (exhaust gas recirculation) valve is to recirculate fuel vapors from the exhaust back through the fuel/air delivery intake. This reduces noxious oxide levels in final exhaust delivery (at the oxygen sensor/s and eventually out of the tail pipe). The EGR valve acts as a go between for the exhaust manifold and the intake manifold. The valve is actuated either by ported vacuum or by using an electric solenoid and motor controlled by a signal from the PCM. When the valve is opened exhaust gases are allowed to enter the intake manifold via passages or tubes.

As these gases enter the intake manifold there are pressure and temperature changes which occur in the intake. Auto manufacturers use differing methods to detect and measure these changes. If conditions are met for EGR valve operation (vehicle speed, throttle position, RPM, etc.) and the correct amount of change is not detected by the corresponding sensor a P0401 code may be stored in the PCM. So, before you purchase just any part; get the correct diagnosis in order to purchase the right part.

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