Ford F150 Pickup. Instruction - part 1374

Fig. 19: Identifying ALT Fuel Solenoid Circuits 
Courtesy of FORD MOTOR CO. 

Testing 

1) Monitor The Fuel Rail Pressure And Fuel Tank Pressure PIDs 

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Key off.  

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Connect the scan tool.  

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Place the ALT fuel switch in the ALT position.  

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Key on, engine off.  

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Access the AFCM.  

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Select the FRPREAB and TANKPR PIDS. 

NOTE:

Verify the ALT fuel tank is filled.

 

2003 Ford Pickup F150 

2003 ENGINE PERFORMANCE Self-Diagnostics - Bi-Fuel - Gasoline/CNG

  

Is the FRPREAB PID greater than 75 psi (517 kPa) and the TANKPR PID greater than 500 psi (3447 
kPa)? If yes, go to step 11) . If the FRPREAB PID is less than 75 psi (517 kPa) and the TANKPR PID is 
greater than 150 psi (1034 kPa), go to next step. If the FRPREAB PID is less than 75 psi (517 kPa) and 
the TANKPR PID is less than 150 psi (1034 kPa), go to step 9) . 

2) Check The Fuel Rail Solenoid 
 

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Key off.  

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Disconnect the fuel rail solenoid connector C1258.  

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Key on, engine off.  

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Access the PCM.  

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Command the fuel pump on.  

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Measure the voltage between the fuel rail solenoid connector C1258 PWR circuit, harness side and 
the fuel rail solenoid connector C1258 ground circuit, harness side. See Fig. 9 .  

Is the voltage greater than 10 volts? If yes, go to step 12) . If no, go to next step. 

3) Check The Fuel Rail Solenoid Ground Circuit For An Open 
 

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Command the fuel pump off.  

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Key off.  

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Measure the resistance between the fuel rail solenoid connector C1258 ground circuit, harness side 
and ground.  

Is the resistance less than 5 ohms? If yes, go to next step. If no, repair the circuit. 

4) Check The ALT Fuel Relay Terminal No. 85 For Voltage 
 

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Key off.  

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Disconnect the ALT fuel relay connector C1293.  

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Key on, engine off.  

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Measure the voltage between the ALT fuel relay connector C1293 terminal No. No. 85, harness 
side and ground. See Fig. 5 .  

Is the voltage greater than 10 volts? If yes, go to next step. If no, repair the circuit. 

5) Check The ALT Fuel Relay Terminal No. 30 For Voltage 
 

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Access the PCM.  

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Command the fuel pump on.  

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Measure the voltage between the ALT fuel relay connector C1293 terminal No. 30, harness side 
and ground.  

Is the voltage greater than 10 volts? If yes, go to next step. If no, repair the circuit. 

 

2003 Ford Pickup F150 

2003 ENGINE PERFORMANCE Self-Diagnostics - Bi-Fuel - Gasoline/CNG

  

6) Check The ALT Fuel Relay Control Circuit For An Open 
 

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Command the fuel pump off.  

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Key on, engine off.  

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Measure the resistance between the ALT fuel relay connector C1293 terminal No. 86, harness side 
and ground.  

Is the resistance less than 5 ohms? If yes, go to step 8) . If no, go to next step. 

7) Check The AFCM For An Internal Open 
 

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Key off.  

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Disconnect the AFCM connector C1427.  

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Measure the resistance between the ALT fuel relay connector C1293 terminal No. 86, harness side 
and the AFCM connector terminal No. 26, harness side.  

Is the resistance less than 5 ohms? If yes, go to step 11) . If no, repair the circuit. 

8) Check The Fuel Solenoid PWR Circuit For An Open 
 

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Measure the resistance between the ALT fuel relay connector C1293 terminal No. 87, harness side 
and the fuel rail solenoid connector C1258 PWR circuit, harness side.  

Is the resistance less than 5 ohms? If yes, install a new ALT fuel relay. If no, repair the circuit. 

9) Check The Fuel Tank Solenoid 
 

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Key off.  

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Disconnect the fuel tank solenoid connector C4129.  

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Key on, engine off.  

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Access the PCM.  

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Command the fuel pump on.  

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Measure the voltage between the fuel tank solenoid connector C4129 PWR circuit, harness side and 
the fuel tank solenoid connector C4129 ground circuit, harness side. See Fig. 10 .  

Is the voltage greater than 10 volts? If yes, install a new fuel tank solenoid. If no, go to next step. 

10) Check The Fuel Tank Solenoid Ground Circuit For An Open 
 

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Command the fuel pump off.  

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Key off.  

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Measure the resistance between the fuel tank solenoid connector C4129 ground circuit, harness side 
and ground.  

 

2003 Ford Pickup F150 

2003 ENGINE PERFORMANCE Self-Diagnostics - Bi-Fuel - Gasoline/CNG

  

Is the resistance less than 5 ohms? If yes, repair the fuel tank solenoid PWR circuit. If no, repair the fuel 
tank solenoid ground circuit. 

11) Check For Correct AFCM Operation 
 

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Disconnect the AFCM.  

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Check for corrosion and pushed out pins.  

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Connect the AFCM connector and make sure it is seated correctly.  

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Operate the system and verify the concern is still present.  

Is the concern still present? If yes, install a new AFCM. If no, the system is operating correctly at this 
time. Concern may have been caused by a loose or corroded connector. 

12) Check The Fuel Pressure Regulator 
 

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Key off. 

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Depressurize the ALT fuel system.  

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Disconnect the fuel pressure regulator inlet and outlet lines.  

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Apply a regulated source of pressurized air to the fuel pressure regulator inlet side.  

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Listen for air escaping from the outlet side.  

Is pressurized air escaping from the outlet side? If yes, install a new fuel rail solenoid. If no, install a new 
fuel pressure regulator. 

TEST AD: NO START - ALT FUEL SWITCH INDICATOR IS ON STEADY 

Diagnostic Aids 

Enter this test only when all steps under QUICK TEST have been successfully completed and engine still does 
not start or if directed here from another test or chart. This test is only intended to diagnose:  

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AFCM  

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Circuitry  

WARNING:

Before performing the following test, go to TEST HC and follow 
the fuel system depressurization procedure. Read all warnings, 
cautions, and notes in test HC.

NOTE:

During bi-fuel diagnostics, intermittent failures are possible. Perform wiggle 
test and tap lightly on relays during testing. Ensure vehicle has CNG before 
continuing with diagnostics.

 

2003 Ford Pickup F150 

2003 ENGINE PERFORMANCE Self-Diagnostics - Bi-Fuel - Gasoline/CNG