This test is a continuation of TEST 7... and here you're gonna' test the ground return circuit of the DPFE sensor.
This ground (for the 5 V REFERENCE Signal) is provided by the PCM, so it's crucial that you take the utmost care not to short this circuit to 12 volts as your are testing/verifying it. Use a multimeter for this test and not a test light.
CASE 1: If your multimeter registered 10-12 Volts: This indicates that the PCM is providing a DPFE sensor ground to the DPFE sensor. If you have gotten to this test by following the following flow of testing: TEST 1, then TEST 2, then TEST 7... then this result indicates that the DPFE sensor is BAD. Replace the DPFE sensor.
CASE 2: If your multimeter DID NOT register 10-12 Volts: Re-check all of your connections and repeat the test. The DPFE sensor will not work without this ground (that the PCM provides) and will set an EGR fault code that will light up the check engine light (CEL) on your instrument cluster. Repairing the issue of this missing ground should solve your EGR valve fault code.
It's very rare for the DPFE Sensor to have any type of issue with its Ground Return Circuit. But if you do encounter this condition and you have triple-checked all of your multimeter's connections and set-up, then the two most likely causes are:
Testing the two above conditions are beyond the scope of this article, but at least you have eliminated the EGR valve, the DPFE sensor, and the EGR Vacuum Regulator Solenoid as the cause of the EGR valve system malfunction.
In this section is input and feedback from all of the folks who have had a similar issue with their vehicle and found a solution. If you're one of them, thank you for sharing your experience with all of us!
If you want to share your repair and/or diagnostic experience, you can use the contact form below.
Vehicle: 1998 Ford F150 XLT
Trouble Codes: P0401.
Test Notes/Repair: “i read all of your suggestions and did everything as you stated. i carefully followed all of your tests to get rid of that dreaded PO401 code.
however, after following all of them, what you failed to mention is that inside the throttle assembly there are two small ports from the EGR valve. these ports were clogged completely. i had to remove the throttle assembly and manually clean them. they were closed shut with carbon.
this solved my problem and i'm sure many others would appreciate this as well.
thanks for a great article!!!!!!!”
Courtesy of: Mario (09-19-2014)
If this info really saved the day, buy me a beer!