Expedition 2WD V8-5.4L (2009)
No
GO to AD3.
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AD3 CHECK THE TRAILER BATTERY CHARGE RELAY (INOPERATIVE)
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Ignition OFF.
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Disconnect: Trailer Battery Charge Relay.
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Substitute a known good relay.
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Ignition ON.
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Measure the voltage between the trailer tow C4099-5, circuit CAT14 (OG) and ground.
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Is the voltage greater than 10 volts?
Yes
REMOVE the known good relay. INSTALL a new trailer battery charge relay. TEST the system for normal operation.
No
REMOVE the known good relay. GO to AD4.
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AD4 CHECK FOR VOLTAGE TO THE TRAILER TOW BATTERY CHARGE RELAY
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Ignition OFF.
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Measure the voltage between the trailer battery charge relay pin 3, circuit SBB21 (GY/RD), BJB face side and ground.
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Is the voltage greater than 10 volts?
Yes
GO to AD5.
No
VERIFY the BJB fuse 21 (30A) is OK. If OK, REPAIR circuit SBB21 (GY/RD) for an open. TEST the system for normal operation. If not OK, REFER
to the Wiring Diagrams to identify the possible causes of the circuit short.
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AD5 CHECK FOR VOLTAGE TO THE TRAILER TOW BATTERY CHARGE RELAY USING THE RELAY GROUND PIN
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Measure the voltage between the trailer battery charge relay pin 3, circuit SBB21 (GY/RD), BJB face side and the trailer battery charge relay pin
2, circuit GD123 (BK/GY), BJB face side.
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Is the voltage greater than 10 volts?
