Hello, i did a key on engine off, as well as a key on engine running diagnostic test on my 89 F150 4x4 (300 inline 6), and i got trouble code 31 (i was expecting a 3 digit code, but i found lots of info on 2 digit codes in another thread, so i guess it's right). Anyway trouble code 31 is "PFE or EVP circuit below minimum voltage of 0.24" Ok, that's all well and good, but what does it mean? What do i do about it? Is it really affecting anything? I'm a lost ball in high weeds here, any help is greatly appreciated. Thanks in advance.

 

Service Code 31 indicates that the EGR Valve Position (EVP) sensor signal is less than the Self-Test minimum value of 0.2 volts.

NOTE:
Because the EVP sensor is preloaded when attached to the EGR valve, a failure in the EGR valve causing the EVP sensor to lose preload may also set code 31.

Possible causes:
--Damaged EVP sensor.
--Damaged EGR valve.
--Open harness.
--Grounded harness.
--Damaged processor.

 

Of the possible causes a bad sensor is the most likely. To test the EGR valve attach engine vacuum directly to it.. the engine should stumble but return to a steady idle when the vacuum is removed. If so then the valve is opening and closing properly. That leaves the EVP sensor mounted on top, you can test it's output with a multimeter and if this confirms it's not within spec change it. See fordfuelinjection for details