94 Explorer DTC 556 help

[jimbrown12]

I have a 94 EB and am getting a KOEO DTC of 556 . This is listed as fuel pump relay primary circuit fault . I immeadiately replaced the fuel pump relay . Still getting the code . Truck starts and runs fine . When I initially start the truck there is no light , after 5 to 10 minutes the check engine light comes back on . I've read a few posts which seem to say that if the truck is running and a relay doesnt do the tirick then the fuel pump is getting old and loosing pressure causing voltage to drop or spike ( not sure which ) . I intend to rent a pressure gauge from Oreilly this weekend and check pressures with engine on and off . Just wnated to know if anyone has had this problem and what fixed it . Thanks in advance ... Happy 4th

Jim Brown

 

[MrShorty]

Could be something wierd, but my experience with these codes is that it either takes a full open or a short to ground for the computer to set the code. As a KOEO code, that circuit fault has to exist at the time you performed the test. Fuel pressure test might be useful, but I think there would be more to be learned with a voltmeter and a wiring diagram. Fuel pump circuit is a pretty basic DC circuit. Don't forget that the fault could be between the PCM and the point where the fuel pump monitor circuit ties into the fuel pump circuit.

 

[jimbrown12]

Thanks ! So sounds like an electrical problem . I'll try but I'm not real good with those . Good news is there's a couple of good shops in town .