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94 Explorer DTC 556 help

jimbrown12

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Joined
November 27, 2002
Messages
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City, State
Spartanburg,SC
Year, Model & Trim Level
94 Eddie Bauer
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
 
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MrShorty

Explorer Addict
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December 27, 2001
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City, State
Spanish Fork, UT
Year, Model & Trim Level
92 XLT and '87 Bronco II
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.
 
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jimbrown12

New Member
Joined
November 27, 2002
Messages
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City, State
Spartanburg,SC
Year, Model & Trim Level
94 Eddie Bauer
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 .
 
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