Rick's Free Auto Repair Advice


P0401 Insufficient EGR Flow

If you have a P0401 Insufficient EGR Flow trouble code, read this to understand what it means

EGR stands for Exhaust Gas Recirculation. At high combustion temperatures, the Nitrogen in the air can combine with the air fuel mixture to produce Oxides of Nitrogen–a key component of smog. To reduce combustion chamber temperatures, the EGR valve opens and sends in a ballast charge of exhaust. Because sending exhaust into the mixture at idle would choke the engine, this is usually done when the engine is running at higher RPMs where it can handle the incoming exhaust.

The computer tells the EGR how much to open, based on engine temperature and RPMs. Then, it monitors how well the EGR actually performed. Every car maker performs the monitoring using a different method. Ford, for example, senses exhaust flow in front of and behind a restriction in the line between the EGR and the intake manifold. The Differential Pressure Feedback Exhaust sensor (DPFE) has a high failure rate. But don’t automatically assume the sensor is bad. You could also have a clogged tube, stuck EGR valve, or a faulty Electric Vacuum Regulator (EVR).

The code can be caused by:

Faulty sensor, blockage in the EGR tube (carbon buildup), stuck or faulty EGR valve, faulty vacuum regulator, broken or leaking vacuum line.

To run tests, click on the “Diagnostic” tab above and scroll down to “By Code” and look for an entry that matches your code and your vehicle.


© 2012 Rick Muscoplat

Posted on by Rick Muscoplat

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