B4000 2WD V6-4.0L OHV (1994)
Fuel Pump Relay: Testing and Inspection
Service Tips
Service Tip
Fuel Pump Relay
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If the Fuel Pump Relay or circuit has an open or short, Diagnostic Trouble Code No. 556 is output.
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If the circuit is open, the engine will not start.
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If the circuit is shorted, the Fuel Pump will operate whenever the ignition switch is On.