Symptoms:

Got a call from customer saying his 2002 Explorer Egr problem showed up as a P0401 code. This code pertains to
insufficient exhaust gas flow fault and he wanted a troubleshooting guide to fix it.

Diagnostics for 2002 explorer egr problem:

When you encounter this P0401 code, the first thing to check is the passages between the egr valve and the exhaust manifold
including the hose connections going to the dpfe sensor.

The dpfe or differential pressure feedback exhaust sensor works like an egr valve regulator by monitoring the engine
exhaust back pressure when opening the egr valve. Inside the sensor is a variable resistor that can detect exhaust
pressure reading being fed with an input voltage called reference voltage. This dpfe sensor has 3 wire connections: reference, voltage return and signal voltage wire.

To test:

Check the top signal wire. When measured, it normally reads 1 volt at idle. The middle wire is usually the reference
voltage wire that reads 5 volt all the time regardless of engine speed. The third wire is return voltage wire.. Now
the top signal wire voltage will vary as the pressure between the two holes where the sensor is located varies. With the engine on idle, apply a hand held suction pump to the egr valve vacuum hose and you will see the signal voltage settles to around 1.0 to 1.2 volt if you apply enough suction. If the voltage does not vary or is stuck on high or low voltage, the sensor is bad.

You can also hold the egr valve diaphragm manually and the engine should start running rough which shows the valve is
working. While doing this, check the voltage at the dpfe signal wire, if the voltage does not changed when you apply
the vacuum, the dpfe sensor is bad.

Final fix for this 2002 explorer egr problem:

Most Ford technicians advised replacing the dpfe sensor when you have P0401 code. Just make sure all wire connections are
secure and not corroded.

If you need a one on one assistance in checking your 2002 explorer egr problem, just let me know. ATS is always there for you!

This is it for today!

Richard