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david, Auto Service Technician
Category: Ford
Satisfied Customers: 1500
Experience:  Certified Master Technician,Certified in diesel & gasoline engines
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1994 Ford Ranger 4x4: 4L engine v6 xlt: My truck dies..freeway

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Disabled Veteran needs work truck to run again...I have a 1994 Ford Ranger 4x4 4L engine v6 xlt: My truck dies suddenly at random times with no warnings. It happens at an idle sometimes and on the freeway other times. The truck runs fine otherwise but this problem happens more and more randomly. Sometimes it will start up again but other times it wont start for a day or two then will fire right up??? I got the diagnostic code 543 secondary fuel pump circuit fault... What does this mean? How do I fix it , what do I need or what should I replace? The fuel pump does come on and I changed the fuel pump relay and it worked for a week or so then it started happening again. Please help me, Thank you so much.

Hi thank you for your question hope this helps.


Diagnostic Trouble Code (DTC) 543 indicates a fuel pump secondary circuit failure between the B(+) supply and the Fuel Pump Monitor (FPM) connection to the power-to-pump circuit. 99 times out of 100, this DTC results in a no-start condition.


If the engine starts and runs, the it is a pretty good indication there is a problem with the Power train Control Module (PCM).


NOTE: Due to the internal circuitry of the Power train Control Module (PCM), a left/front Heated Oxygen Sensor (HO2S) signal short to power could produce a Diagnostic Trouble Code (DTC) 542 or 543. So be for replacing the PCM replace the Front Drivers side 02 sensor. But with your no start and engine stalling i am thinking PCM failure.


Hope this helps

Good luck

david and 3 other Ford Specialists are ready to help you
Customer: replied 8 years ago.
Do you think getting a PCM from a junk yard would be okay? Is there any way to test the PCM? Could I take my PCM to a Ford dealership to have it tested? The bottom nut on the PCM looks tough to get on and off, any tricks? Thank you for your help.

First a junk yard PCM is a crap shoot you wont to look for one that is not from a truck that has been in a reck. Yes the a ford dealership can test the PCM.


My trick for getting the bottom nut is 1/4 inch ratchet and a long extension.


To remove

  1. Disconnect the negative battery cable.
  2. Disengage the wiring harness connector from the PCM by loosening the connector retaining bolt, then pulling the connector from the module.
  3. Remove the two nuts and the PCM cover.
  4. Remove the PCM from the bracket by pulling the unit outward.


To install:

  1. Install the PCM in the mounting bracket.
  2. Install the PCM cover and tighten the two nuts.
  3. Attach the wiring harness connector to the module, then tighten the connector retaining bolt.
  4. Connect the negative battery cable.



Customer: replied 8 years ago.
Is it possible for it to be the Ignition Control Modual? Or could it be a groud?

i would not thing a ground would give this problem because in this case the battery power is not getting to the fuel pump circuit witch is feed throw the PCM. but you could give it a try stranger things have happened.


As for the ICM you would have different problem's along with Diagnostic codes. something along the lines of bad communication codes or faulty communication codes