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94 Explorer DTC 556 help

jimbrown12

New Member
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
 




MrShorty

Explorer Addict
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December 27, 2001
Messages
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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.
 




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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