Ford F150 Pickup. Instruction - part 1394

Turn ignition off. Disconnect bi-fuel relay module power supply harness connector C495. Disconnect 
compuvalve harness connector C1294. Ensure bi-fuel relay module connector C410 is disconnected. 
Using DVOM, measure resistance between chassis ground and bi-fuel relay module harness connector 
C410M terminal "A". Also, measure resistance between specified compuvalve harness connector 
terminals and bi-fuel relay module harness connector terminals. See COMPUVALVE MAIN 
HARNESS CONTINUITY TEST table. See Fig. 7 and Fig. 15 . If all resistances are less than 5 ohms, 
perform COMPUVALVE CHECK under QUICK TEST. If no-start fault still exists, replace 
compuvalve. If any resistance is 5 ohms or more, repair open in affected circuit. See ENGINE 
PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. 

COMPUVALVE MAIN HARNESS CONTINUITY TEST 

8) Check ALT Fuel Switch Circuit Voltage 
 
Turn ignition off. Disconnect compuvalve 10-pin in-line harness connector C422, located in rear right 
side of engine compartment. Turn ignition on. Using DVOM, measure voltage between chassis ground 
and in-line harness connector C422M terminal "E". See Fig. 15 . If voltage is 10 volts or less, go to next 
step. If voltage is more than 10 volts, go to step 10) . 

9) Check Power To ALT Fuel Switch 
Turn ignition off. Disconnect bi-fuel relay module power supply harness connector C495. Disconnect bi-
fuel relay harness connector C410. Reconnect bi-fuel relay module power supply harness connector 
C495. 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" and "E" (White wires). See Fig. 15 . If both voltages are more 
than 10 volts, replace compuvalve main harness. If either voltage is 10 volts or less, replace bi-fuel relay 
module. 

10) Check Circuits To ALT Fuel Switch 

Bi-Fuel Relay Harness Connector C410M 
Terminal

Compuvalve Harness Connector C1294 Terminal

No.

"C"

2

"B"

5

"D"

9, 11 & 13

"E"

9, 11 & 13

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:

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

 

2003 Ford Pickup F150 

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

  

 
Ensure compuvalve 10-pin in-line harness connector C422 is disconnected. Place ALT fuel switch in 
ALT position. Using DVOM, measure resistance between in-line harness connector C422F terminal 
"F" (Yellow wire) and terminal "H" (Dark Green wire). See Fig. 15 . If resistance is 5 ohms or more with 
switch in ALT position, go to next step. If resistance is less than 5 ohms with switch in ALT position, go 
to step 12) . 

11) Check ALT Fuel Switch Operation 
 
Disconnect ALT fuel switch 3-pin connector C4013. Place ALT fuel switch in ALT position. Using 
DVOM, measure resistance between ALT fuel switch connector C4013M terminal "B" (Yellow wire) and 
terminal "C" (Dark Green wire). See Fig. 3 . If resistance is less than 5 ohms, repair open in affected 
circuit between ALT fuel switch connector C4013 and compuvalve in-line harness connector C422. If 
resistance is 5 ohms or more, check for open in Yellow or Dark Green wires between ALT fuel switch 
connector C4013 and ALT fuel switch. See ENGINE PERFORMANCE in SYSTEM WIRING 
DIAGRAMS article in ELECTRICAL. Repair as necessary. If circuits are okay, replace ALT fuel switch. 

12) Check Circuit Between ALT Fuel Switch & Compuvalve 
Turn ignition off. Disconnect bi-fuel relay module power supply harness connector C495. Disconnect 
compuvalve harness connector C1294. Using DVOM, measure resistance of White wire between 
compuvalve harness connector C422M terminal "F" and compuvalve harness connector C1294 terminal 
No. 46. See Fig. 7 and Fig. 15 . If resistance is less than 5 ohms, perform COMPUVALVE CHECK 
under QUICK TEST. If no-start fault still exists, replace compuvalve. If resistance is 5 ohms or more, 
repair open in White wire between compuvalve harness connector C422 and compuvalve harness 
connector C1294. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in 
ELECTRICAL.  

TEST AC: NO START - ALT FUEL SWITCH INDICATOR IS ON, THEN 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

Solenoid tank valve/lockoff solenoid.  

z

Alternate fuel lines and filters.  

z

Compuvalve.  

CAUTION: Be very careful when probing compuvalve harness connector 

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

NOTE:

This fault can be mistaken as an auto switch to GAS mode condition. Verify 
LPG fuel level using fuel gauge mounted to LPG tank before continuing 
diagnostics. Ensure instruction shutoff valves (1/4 turn valves) and manual tank 
valves (if equipped) are open.

 

2003 Ford Pickup F150 

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

  

Testing 

1) Check For DTCS 
Turn ignition off. Connect scan tool to Data Link Connector (DLC). Turn ignition on. Using scan tool, 
access PCM and retrieve any stored DTCs. Using scan tool, access AFCM and record any stored DTCs. If 
any PCM DTCs are present, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-
DIAGNOSTICS - CNG, FLEX-FUEL & GASOLINE article. If any AFCM DTCs are present, go to 
DIAGNOSTIC TROUBLE CODE DEFINITIONS and repair as necessary. If no DTCs are present, go 
to next step. 

2) Verify No-Start Concern 
Place ALT fuel switch is in ALT position. Attempt to start engine. If engine starts with ALT fuel switch 
in ALT position, ALT fuel system is operating properly at this time. If concern is intermittent, see 
INTERMITTENTS in TROUBLE SHOOTING - NO CODES - BI-FUEL - GASOLINE/LPG article. If 
engine does not start with ALT fuel switch in ALT position, go to next step. 

3) Access AFCM FRPREAB PID 
Connect scan tool to DLC. Using scan tool, access AFCM and select FRPREAB PID from PID/DATA 
MONITOR & RECORD menu. Turn ignition off, then on. Select FRPREAB PID from PID/DATA 
MONITOR & RECORD menu and record value. Monitor FRPREAB PID. If FRPREAB PID value is 
less than 26 psi, go to next step. If FRPREAB PID value is 26 psi or more (LPG), go to step 10) . 

4) Monitor FRPREAB PID Leakdown 
Ensure scan tool is connected to DLC. Using scan tool, access AFCM and monitor FRPREAB PID from 

NOTE:

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

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:

Ensure EEC system calibration is for current Bi-Fuel code. On LPG 
equipped vehicles, Engine Coolant Temperature (ECT) must above 20°F (-
7°C) or ALT fuel system may default to GAS mode.

NOTE:

Minimum FRPREAB PID values required to illuminate ALT fuel selector 
switch indicator is 26 psi.

NOTE:

Before beginning leakdown test, check all fuel connections at vaporizer, 
regulator, and compuvalve for leaks. See LEAK TEST - ALL BI-FUEL 
VEHICLES under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 
BI-FUEL - GASOLINE/LPG article.

 

2003 Ford Pickup F150 

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

  

PID/DATA MONITOR & RECORD menu. Turn ignition off, then on. Record FRPREAB PID value at 
ignition on. Wait 2 minutes. If FRPREAB PID value drops 10 psi or more, go to step 10) . If FRPREAB 
PID drops less than 10 psi, go to next step. 

5) Check Fuel Level, Tank Valve & Fuel Filter 
On LPG models, close tank valve and then fully open tank valve (open slowly to ensure excess flow 
valve does not close). Tank valve is located on LPG fuel tank. For additional information, see 
LIQUEFIED PETROLEUM GAS FUEL TANK EVACUATING under FUEL SYSTEM PRESSURE 
RELEASE under FUEL SYSTEMS in REMOVAL & INSTALLATION - F150 PICKUP - BI-FUEL - 
GASOLINE/LPG article. Turn ignition on. Using scan tool, access AFCM and select FTP PID from 
PID/DATA MONITOR & RECORD menu. Monitor FTP PID. Proceed as follows: 

z

If FTP PID value is less than 26 psi, go to next step.  

z

If FTP PID value is 26 psi or more, start engine in ALT fuel mode to ensure concern is no longer 
present.  

6) Check Vaporizer Lockoff Solenoid Signal 
Turn ignition off. Disconnect in-line harness connector C4002. Connect a test light between in-line 
harness connector C4002F terminal "D" and "F" (both White wires). See Fig. 28 . Observe test light and 
turn ignition on. If test light illuminates momentarily when ignition is turned on, go to next step. If test 
light does not illuminate when ignition is turned on, go to step 8) . 

7) Check Lockoff Solenoid Coil Resistance 
Turn ignition off. Ensure in-line harness connector C4002 is disconnected. Gently wiggle connection and 
flex wires around diode splice. Diode is located in harness near connector. Resistance value must remain 
within one ohm while wires are being flexed and connection wiggled. 

Using DVOM, measure resistance between in-line harness connector C4002M terminal "D" (White wire) 
and terminal "F" (Yellow wire). See Fig. 28 . If resistance is 8-18 ohms, replace mechanically stuck 
lockoff solenoid. If resistance is not 8-18 ohms, replace lockoff solenoid for internal open circuit. See 
under FUEL SYSTEMS LOCKOFF SOLENOID in REMOVAL & INSTALLATION - F150 PICKUP 
- BI-FUEL - GASOLINE/LPG article. 

NOTE:

Before beginning the leakdown test, check all fuel connections at the 
vaporizer, regulator, and compuvalve for leaks.

CAUTION: When connecting test light, DO NOT short across terminals as 

damage to compuvalve may occur.

NOTE:

This circuit is powered from inertia switch. Test light will only illuminate 
momentarily.

CAUTION: DO NOT bend diode or flex wires more than 30 degrees.

 

2003 Ford Pickup F150 

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