Ford F150 Pickup. Instruction - part 1375

Fig. 20: Identifying ALT Fuel Injector Circuits 
Courtesy of FORD MOTOR CO. 

Testing 

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

z

Key off.  

z

Connect the scan tool.  

z

Place the ALT fuel switch in the ALT position.  

z

Key on, engine off.  

z

Access the AFCM.  

z

Select the FRPREAB and TANKPR PIDS.  

Is the FRPREAB PID greater than 75 psi (517 kPa) and the TANKPR PID greater than 150 psi (1034 
kPa)? If yes, go to next step. If no, go to TEST AC . 

2) Check The ALT Fuel Injector VPWR Circuit 
 

z

Key off. 

z

Disconnect two ALT fuel injectors.  

z

Key on, engine off.  

z

Measure the voltage between the right bank ALT fuel injector VPWR circuit, harness side and 
ground; and between the left bank ALT fuel injector VPWR circuit, harness side and ground.  

Are the voltages greater than 10 volts? If yes, go to next step. If no, repair the circuit in question.

NOTE:

Verify the ALT fuel tank is filled.

NOTE:

Check at least one fuel injector on each bank.

 

2003 Ford Pickup F150 

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

  

3) Check The ALT Fuel Injector Driver Circuit 
 

z

Connect a test lamp between the right bank ALT fuel injector VPWR circuit, harness side and the 
right bank ALT fuel injector driver circuit, harness side; and between the left bank ALT fuel 
injector VPWR circuit, harness side and the left bank ALT fuel injector driver circuit, harness side. 

z

Crank the engine.  

Does the test lamp blink consistently and brightly (one blink per engine revolution) for each bank? If yes, 
the ALT fuel control system is functioning correctly. See SYMPTOMS in TROUBLE SHOOTING - NO 
CODES - BI-FUEL - GASOLINE/CNG article to continue diagnosis. If no, go to next step. 

4) Check For Correct AFCM Operation 
 

z

Disconnect the AFCM.  

z

Check for corrosion and pushed out pins.  

z

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

z

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. 

TEST AE: NO START - ALT FUEL SWITCH INDICATOR IS OFF 

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:  

z

ALT Fuel Switch  

z

AFCM  

z

Circuitry  

NOTE:

Check at least one fuel injector on each bank.

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

  

Fig. 21: Identifying ALT Fuel Switch/Indicator Circuit 
Courtesy of FORD MOTOR CO. 

Testing 

1) Check The ALT Fuel Switch PID 
 

z

Place the ALT fuel switch in the ALT position.  

z

Connect the scan tool.  

z

Key on, engine off.  

z

Access the AFCM.  

z

Select the SEL_SW PID.  

Does the SEL_SW PID indicate ALT? If yes, go to step 5) . If no, go to next step. 

2) Check The ALT Fuel Switch VPWR Circuit 
 

z

Key off.  

z

Disconnect the ALT fuel switch connector.  

z

Key on, engine off.  

z

Measure the voltage between the ALT fuel switch connector VPWR circuit, harness side and 
ground. See Fig. 21 .  

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

3) Simulate An ALT Fuel Switch Input 
 

z

Access the AFCM.  

z

Select the SEL_SW PID.  

z

Connect a 5-amp fused jumper between the ALT fuel switch connector VPWR circuit, harness side 
and the ALT fuel switch connector input circuit, harness side. 

 

2003 Ford Pickup F150 

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

  

Does the SEL_SW PID indicate ALT? If yes, install a new ALT fuel switch. If no, go to next step.

4) Check The ALT Fuel Switch Input Circuit For An Open 
 

z

Key off.  

z

Disconnect the AFCM connector C1427.  

z

Measure the resistance between the ALT fuel switch connector input circuit, harness side and the 
AFCM connector C1427 terminal No. 42, harness side. See CONNECTOR IDENTIFICATION . 

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

5) Check The ALT Fuel Indicator Control Circuit 
 

z

Key off.  

z

Disconnect the AFCM connector C1427.  

z

Key on, engine off.  

z

Connect a 5-amp fused jumper between the AFCM connector C1427 terminal No. 24, harness side 
and ground. See CONNECTOR IDENTIFICATION .  

Is the ALT fuel indicator illuminated? If yes, go to step 8) . If no, go to next step. 

6) Check The ALT Fuel Indicator PWR Circuit 
 

z

Key off.  

z

Disconnect the ALT fuel switch connector.  

z

Key on, engine off.  

z

Measure the voltage between the ALT fuel switch connector indicator PWR circuit, harness side 
and ground. See Fig. 21 .  

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

7) Check The ALT Fuel Indicator Control Circuit For An Open 
 

z

Key off.  

z

Measure the resistance between the ALT fuel switch connector indicator control circuit, harness 
side and the AFCM connector terminal No. 24, harness side.  

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

8) Check For Correct AFCM Operation 
 

z

Disconnect the AFCM.  

z

Check for corrosion and pushed out pins.  

z

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

 

2003 Ford Pickup F150 

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