Ford F150 Pickup. Instruction - part 1393

connector terminals, see Fig. 30 . DO NOT connect any test light unless specified in testing procedure. 
All measurements are made by probing rear of connector (wiring harness side). Isolate both ends of a 
circuit and turn ignition switch to OFF position when checking for shorts or continuity, unless instructed 
otherwise.  

4. Disconnect solenoids and switches from harness before measuring continuity and resistance or applying 

voltage. After each repair, check all component connections and repeat QUICK TEST .  

5. An open circuit is defined as a resistance reading of 5 ohms or more. This specification tolerance may be 

too high for some items in EEC-V system. If resistance approaches 5 ohms, always clean suspect 
connector and coat it with protective dielectric silicone grease. A short is defined as a resistance reading 
of 10,000 ohms or less to ground, unless stated otherwise in system test.  

6. If instructed to replace Powertrain Control Module (PCM) after performing a system test, new PCM must 

be programmed. See POWERTRAIN CONTROL MODULE under PROGRAMMING.  

TEST AA: NO START - GASOLINE MODE 

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

Fuel pump intercept circuits from fuel pump cutoff relay.  

z

Bi-fuel relay module.  

z

Harness circuits.  

CAUTION: Perform all resistance and voltage tests with a Digital Volt-Ohmmeter 

(DVOM) with minimum 10-megohm impedance, unless stated otherwise in 
test procedures. Ensure ignition switch is turned to OFF position when 
performing resistance tests.

NOTE:

For identification of circuits, components, terminals and wire colors referenced 
in the following testing, see ENGINE PERFORMANCE in appropriate SYSTEM 
WIRING DIAGRAMS article in ELECTRICAL. For connector locations, see 
CONNECTOR LOCATION table. To prevent replacement of good components, 
be aware the following non-EEC related areas and components may be cause of 
problem: 

z

Fuel quality and quantity.  

z

Ignition (general condition).  

z

Engine mechanical components.  

z

Starter and battery circuits.  

NOTE:

During bi-fuel diagnostics, intermittent failures are possible. Perform wiggle 
test and tap lightly on relays during testing.

 

2003 Ford Pickup F150 

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

  

Testing 

1) By-Pass Fuel Pump Intercept Circuits 
Turn ignition off. Disconnect fuel pump intercept harness connectors C463 and C4131. See Fig. 10 and 
Fig. 12 . Connector C463 and C4131 are located in center of vehicle, near fuel tank. Move fuel pump 
intercept harness aside and reconnect base vehicle fuel pump harness connectors. Place ALT fuel switch 
in GAS position. Attempt to start engine. If engine starts with ALT fuel switch in GAS position, go to 
next step. If engine does not start with ALT fuel switch in GAS position, repair base vehicle gasoline fuel 
concern. See NO-START/NORMAL CRANK under SYMPTOMS in TROUBLE SHOOTING - NO 
CODES - CNG, FLEX-FUEL & GASOLINE article. 

2) Check Bi-Fuel Relay Operation 
Turn ignition off. Disconnect bi-fuel relay module power supply harness connector C495. See Fig. 6 . 
Also, disconnect bi-fuel relay module harness connectors C410 and C4001. Using DVOM, measure 
resistance between bi-fuel relay module harness connector C4001F terminals No. 1 and 2. See Fig. 4 and 
Fig. 15 . If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, replace bi-fuel 
relay module. 

3) Check Fuel Pump Intercept Harness 
 
Ensure ignition is off. Reconnect fuel pump intercept harness connectors C463 and C4131. Connect a 
fused jumper wire (5-amp) between bi-fuel relay module harness connector C4001M terminals No. 1 and 
2. Ensure ALT fuel switch is in GAS position. Attempt to start engine. If engine starts with ALT fuel 
switch in GAS position, go to next step. If engine does not start with ALT fuel switch in GAS position, 
repair or replace fuel pump intercept harness (Pink/Black wire) between bi-fuel relay module and fuel 
tank unit. See ENGINE PERFORMANCE in appropriate SYSTEM WIRING DIAGRAMS article in 
ELECTRICAL. 

4) Check Bi-fuel Relay Module 
 
Ensure ignition is off. Reconnect bi-fuel relay module connector C410 and bi-fuel relay module power 
supply connector C495. Ensure ALT fuel switch is in GAS position. Turn ignition on. Using DVOM, 
measure resistance between bi-fuel relay module connector C4001F terminals No. 1 and 2. If resistance is 
5 ohms or more, go to next step. If resistance is less than 5 ohms, reconnect all connectors and restart 
engine. If no-start fault still exists, go to next step. 

5) Check Main Harness 
 

CAUTION: Always disconnect bi-fuel relay module power supply 3-pin harness 

connector C495 before disconnecting or reconnecting compuvalve 
main harness connector C1294 to avoid damaging compuvalve or 
connectors. See Fig. 6 .

NOTE:

During bi-fuel relay module, fuse, and relay diagnostics, intermittent 
failures are possible. During each continuity test a wiggle test should also 
be performed, including tapping relays during testing.

 

2003 Ford Pickup F150 

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

  

Turn ignition off. Ensure bi-fuel relay module harness connector C4001 is disconnected. Ensure ALT fuel 
switch is in GAS position. Using DVOM, measure and record resistance between bi-fuel relay module 
connector C4001F terminals No. 1 and 2. Turn ignition on. Using DVOM, again measure resistance 
between bi-fuel relay module connector C4001F terminals No. 1 and 2. If resistance less than 5 ohms 
with ignition off and more than 10 k/ohms with ignition on, go to next step. If resistance 5 ohms or more 
with ignition off and 10 k/ohms or less with ignition on, reconnect bi-fuel relay module connector C4001. 
If no-start fault still exists, replace bi-fuel relay module. 

6) Check Compuvalve 
 
Turn ignition off. Disconnect bi-fuel relay module power supply connector C495. Disconnect 
compuvalve 64-pin harness connector C1294. Compuvalve is located in right side, rear of engine 
compartment. Using DVOM, measure resistance between chassis ground and compuvalve harness 
connector C1294F terminal No. 5. See Fig. 7 . If resistance is more than 10 k/ohms, perform 
COMPUVALVE CHECK under QUICK TEST. If no-start fault still exists, replace compuvalve. If 
resistance is 10 k/ohms or less, repair short to ground in White wire between compuvalve harness 
connector C1294F terminal No. 5 and bi-fuel relay module harness connector C410M terminal "B". See 
ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.  

TEST AB: NO START - ALT FUEL SWITCH INDICATOR 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

Bi-fuel relay module.  

z

Compuvalve.  

z

Harness circuits.  

If vehicle is equipped with dual LPG tanks, check operation using both tanks. 

Testing 

1) Check Communication With AFCM 
Connect scan tool to Data Link Connector (DLC). Turn ignition on. Using scan tool, select vehicle and 
engine. Select AFCM-ALTERNATE FUEL CONTROL MODULE. Access FAP, OPMODE, and 
SWITCH PIDS from PID/DATA MONITOR & RECORD menu. If communication with AFCM is 

NOTE:

During bi-fuel diagnostics, intermittent failures are possible. Perform wiggle 
test and tap lightly on relays during testing.

CAUTION: Always disconnect bi-fuel relay module power supply 3-pin harness 

connector C495 before disconnecting or reconnecting compuvalve 
main harness connector C1294 to avoid damaging compuvalve or 
connectors. See Fig. 6 .

 

2003 Ford Pickup F150 

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

  

possible go to step 8) . If communication between scan tool and AFCM is not possible, go to next step. 

2) Check Bi-Fuel Relay Module Fuse No. 1 (3-Amp) 
 
Remove and inspect bi-fuel relay module fuse No. 1 (3-amp) located in bi-fuel relay module. See Fig. 5 . 
Bi-fuel relay module is located on left side, rear of engine compartment. If fuse is okay, go to next step. If 
fuse is blown, replace fuse and retest system. 

3) Check Ground To Bi-Fuel Relay Module 
 
Disconnect bi-fuel relay module harness connector C410. Using DVOM, measure resistance between 
chassis ground and bi-fuel relay module C410M terminal "A". If resistance is less than 5 ohms, reconnect 
bi-fuel relay module harness connector C410 and go to next step. If resistance is 5 ohms or more, repair 
open in ground circuit to bi-fuel relay module. See ENGINE PERFORMANCE in SYSTEM WIRING 
DIAGRAMS article in ELECTRICAL. 

4) Check Voltage To Bi-Fuel Relay Module 
 
Turn ignition off. Disconnect bi-fuel relay module power supply harness connector C495. Turn ignition 
on. Using DVOM, measure voltage between chassis ground and bi-fuel relay module power supply 
harness connector C495F terminals "A" and "B". See Fig. 6 . If both voltages are more than 10 volts, go 
to next step. If either voltage is 10 volts or less, repair open or short in affected circuit. See ENGINE 
PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. 

5) Check KAPWR Output From Bi-Fuel Relay Module 
 
Disconnect bi-fuel relay module connector C410. Connect bi-fuel relay module power supply connector 
C495. Using DVOM, measure voltage between chassis ground and bi-fuel relay module C410F terminal 
"C". See Fig. 15 . If voltage is more than 10 volts, go to next step. If voltage is 10 volts or less, replace bi-
fuel relay module. 

6) Check VPWR Output From Bi-Fuel Relay Module 
Ensure bi-fuel relay module connector C410 is disconnected. Turn ignition on. Connect a 5-amp fused 
jumper wire between chassis ground and bi-fuel relay module harness connector C410F terminal "A". 
Using DVOM, measure voltage between chassis ground and bi-fuel relay module harness connector 
C410F terminals "D", "E", "F", "G", "H" and "J" (White wires). See Fig. 15 . If all voltages are more than 
10 volts, go to next step. If either voltage is 10 volts or less, replace bi-fuel relay module. 

7) Check Compuvalve Main Harness 

NOTE:

Bi-fuel power relay should "click" when harness connector C410F terminal 
"A" is grounded.

CAUTION: Be very careful when probing compuvalve harness connector 

terminals. These terminals can be damaged if overstressed, resulting 
in harness replacement.

 

2003 Ford Pickup F150 

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