I have a '97 F150, 4wd with 4.6l engine. My check engine light keeps coming on with code P0401. I've replaced the EGR valve, the DPFE sensor and the EGR vacuum regulator. I've disassembled and cleaned the ports from the EGR to the intake. If I apply vacuum to the EGR valve, the engine stumbles as it opens. The vacuum lines seem to be ok. I have vacuum coming to the EGR vacuum regulator. I can reset the code but soon it will come back on. Does this mean the PCM is defective or is there something else I'm overlooking?

 

2 things come to mind, either the wires from the pcm to the egr solenoid are shorted to ground or open or the pcm is bad. The sensor itself is working and telling the pcm it's not seeing it open/closed when commanded.
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Thanks for the advice, Rnlcomp. There isn't much left that it could be. The next thing to check will be the wiring. Then I guess it's the PCM.