2002 Ford F150 4.2L: Diagnostic Code 1401

Code 1401 on a 2002 Ford F-150 truck with a 4.2-liter engine indicates the Differential Pressure Feedback EGR, or DPFE, circuit voltage is too high. The DPFE senses the differential pressure in the exhaust opposed to the gas pressure in the intake manifold. It signals this differential to the computer. The computer in turn operates the EGR vacuum solenoid to open the EGR, allowing exhaust gases to enter the intake manifold. This is essential in reducing the combustion temperatures, thus reducing oxides of nitrogen, which are toxic to the environment.

Instructions

1

Locate the DPFE sensor on the rear of the engine close to the EGR valve. It is a box with two hoses on the bottom, one leading to the exhaust and one to the intake manifold. It has a three-wire plug in the side. In most cases, a Ford truck has the sensor mounted to a bracket on the rear of the engine. In some cases, it is on the firewall.

2

Pull the two hoses off the sensor and look in the hoses to see if they are plugged up by a white-looking powder. If so, pull them off the lower metal lines as well and blow out the hoses. Install them on the proper lower metal lines and to the DPFE sensor. The sensor does not operate if the hoses are blocked.

3

Start the engine and allow it to warm up for a few minutes. To accurately test everything, the engine must be at least warm. The computer does not allow the system to function at all when the engine is cold. It determines this through the coolant temperature sensor. Shut off the engine.

4

Pull the vacuum line off the EGR vacuum diaphragm and install the handheld vacuum pump. Connect the black voltmeter lead to the battery negative terminal. Use the sharp point on the red leads probe to pierce the uppermost of the three wires on the DPFE sensor.

5

Start the engine and observe the voltmeter. Look for very close to 0.9 volts. Apply vacuum to the EGR vacuum diaphragm. The voltage should rise to 3 to 4.5 volts as vacuum is applied. The EGR opening, through the introduction of a vacuum, causes the engine to run very rough or stall. As the vacuum is released, the voltage returns to the beginning value of 0.9 volt and the engine again runs smoothly. If the reaction is as described, the sensor is good. If the sensor does not have a rise in voltage as vacuum was applied and drop as it is exhausted, the sensor is bad.

6

If no voltage is present, the wire from the sensor to the computer has an open or if found to have continuity to the computer, the computer driver circuit itself is bad and the computer needs to be replaced. If the sensor was found to be working properly, move to the next step, which is checking the EGR vacuum solenoid. This solenoid is close to the EGR and has two wires in the plug and two vacuum lines: one line from the vacuum source on the intake manifold and the other to the EGR vacuum diaphragm.

7

Locate the electrical plug on the vacuum-regulating solenoid. The red with a yellow stripe is the power, and the brown wire with a pink stripe is the computer ground control wire connected to terminal 47 on the computer. When the DPFE and coolant temperature signals are received by the computer, it senses engine load by the pressure differential and grounds the vacuum regulator solenoid, making it open. In response to its activation, the regulator solenoid opens and allows manifold vacuum through to the EGR vacuum diaphragm, then the EGR opens.

8

Verify the functioning of the vacuum regulator solenoid for the EGR. A word of warning: The engine is running for this test and the EGR is hot. You will be an unhappy camper if you touch the EGR. Carefully remove the two vacuum hoses on the bottom of the solenoid. The green hose is the one from the vacuum source on the intake manifold to the solenoid, and the other hose is the feed hose to the EGR vacuum diaphragm when the solenoid is open.

9

Start the truck and feel for a vacuum on the hose from the intake manifold. If a vacuum is present, shut off the engine. If no vacuum is present, check the vacuum hose to the manifold for cracks, looseness or a clog. It must have a vacuum to operate.

10

Plug the hoses into the solenoid. Connect the black voltmeter lead to the battery negative terminal. Use the red leads probe to pierce the right side wire. Turn the ignition on and observe the voltage. It has 12 volts if the circuit is good. If no voltage is present, trace the wire, looking for a short or open. Repair the problem with the wire and retest. Turn the ignition off.

11

Test the flow of vacuum on the vacuum regulator solenoid. The best way to do this for positive proof it is working is to test-drive the truck while watching the vacuum gauge. Pull the vacuum line off the solenoid to the EGR vacuum diaphragm at the solenoid. Connect the long vacuum line on the solenoid. Place it up between the rear of the hood and the windshield. Close the hood and attach the vacuum pump to the hose and place it behind the wiper arm. While test-driving the truck for a short distance, observe the gauge. When accelerating, the vacuum gauge shows five inches HG of vacuum; as soon as the pedal is released, the vacuum should drop to zero. If all is well, the solenoid is good. If it fails to indicate the five inches HG, the solenoid is bad and needs to be replaced. Shut the engine off and remove the vacuum hose to the vacuum pump at the solenoid. Replace the vacuum hose from the diaphragm to the solenoid.