Ford F150 Pickup. Instruction - part 1397

under FUEL SYSTEMS in REMOVAL & INSTALLATION - F150 PICKUP - BI-FUEL -
GASOLINE/LPG article. Ensure scan tool is connected to DLC. Turn ignition on. Access AFCM and 
select FRPREAB PID from PID/DATA MONITOR & RECORD menu. If FRPREAB PID reading is 
more than 60 psi, perform COMPUVALVE CHECK under QUICK TEST. If fault still exists, replace 
compuvalve. If FRPREAB PID reading is 60 psi or less, replace fuel vaporizer. See VAPORIZER (LPG 
FUEL HEATER) under FUEL SYSTEMS in REMOVAL & INSTALLATION - F150 PICKUP - BI-
FUEL - GASOLINE/LPG article.  

TEST H: FUEL CONTROL 

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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Heated Oxygen Sensor (HO2S).  

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HO2S and VPWR circuits and connections.  

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Compuvalve.  

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Vacuum systems.  

HO2S-11 and HO2S-21 circuits are monitored by compuvalve. Information is used by compuvalve for fuel trim 
calculations. HO2S PID should vary between 0-0.3 and 0.6-1.0 volt while engine is operating at 2000 RPM. 
Also, a change from rich to lean should occur more than 5 times during a period of 10 seconds at 2000 RPM. 
DTCs P0131, P0132, P0134, P0151, P0152, P0154, P0171, P0172, P0174 and P0175 are unique to alternative 
fuel system and are set if compuvalve receives a continuously high or low input (more than or less than 0.55 
volt for more than 120 seconds), or no activity from HO2S. Possible causes for these faults are:  

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HO2S circuits are open or shorted to ground.  

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Faulty HO2S sensor.  

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Consistently lean or rich fuel system  

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Faulty compuvalve.  

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Faulty harness circuits (HO2S or VPWR).  

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Intake air leaks.  

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Plugged injectors.  

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Pressure regulator inoperative.  

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Exhaust leaks.  

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PCV system.  

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Ignition system faults.  

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Low compression.  

HO2S SENSOR OPERATING VOLTAGE SPECIFICATIONS 

Condition

HO2S-11 Voltage

HO2S-21 Voltage

KOEO

Below One

Below One

 

2003 Ford Pickup F150 

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

  

Testing 

1) Access PCM DTCs 
 
Place ALT fuel switch in GAS mode. Start engine and allow it to reach normal operating temperature. 
Connect scan tool to Data Link Connector (DLC). Using scan tool, access PCM and record KOEO, 
KOER and Continuous Memory PCM DTCs. If any PCM DTCs are present, go to DIAGNOSTIC 
TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - CNG, FLEX-FUEL & GASOLINE 
article and service DTCs as necessary. If no KOEO, KOER or Continuous Memory PCM DTCs are 
present, go to next step. 

2) Access PCM PIDs 
Ensure engine is at normal operating temperature. Ensure scan tool is connected to DLC. Turn ignition 
on. Using scan tool, access PCM and select HO2S-11 or HO2S-21 PID from PID/DATA MONITOR & 
RECORD menu. Start engine and observe HO2S PIDs. HO2S PIDs should switch between zero and one 
volt at idle. If HO2S PIDs are within specification, go to next step. If HO2S PIDs are not within 
specification, go to HEATED OXYGEN SENSOR MONITOR under DIAGNOSTIC MONITORS in 
SELF-DIAGNOSTICS - CNG, FLEX-FUEL & GASOLINE article and diagnose appropriate HO2S. 

3) Access AFCM PIDs In GAS Mode 
Ensure engine is at normal operating temperature. Ensure ALT fuel switch is in GAS position. Using scan 
tool, access AFCM and select HO2S-11 or HO2S-21 PID from PID/DATA MONITOR & RECORD 
menu. Start engine in GAS mode and observe HO2S PID. HO2S PIDs should switch between zero and 
one volt at idle. If HO2S PIDs are not within specification, go to step 5) . If HO2S PIDs are within 

At Idle

(1)

(1)

Deceleration

0-0.4

0-0.4

Acceleration

0.5-1.0

0.5-1.0

(1)

Switching between zero and one volt.

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

NOTE:

HO2S-11 (right) and HO2S-21 (left) refer to upstream HO2S.

NOTE:

HO2S may be displayed as O2S on scan tool.

NOTE:

HO2S may be displayed as O2S on scan tool.

 

2003 Ford Pickup F150 

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

  

specification, go to next step. 

4) Access AFCM PIDs In ALT Fuel Mode 
 
Ensure engine is at normal operating temperature. Ensure ALT fuel switch is in ALT position. Using scan 
tool, access AFCM and select HO2S-11 or HO2S-21 PID from PID/DATA MONITOR & RECORD 
menu. Start engine in ALT mode and observe HO2S PID. HO2S PIDs should switch between zero and 
one volt at idle. If HO2S PIDs are not within specification, check for leaks around ALT fuel supply 
system and repair as necessary. Check for kinked or bent fuel lines or blockage in injector sleeves or rails. 
Repair as necessary. If HO2S PIDs are within specification, perform COMPUVALVE RESET 
procedure under PROGRAMMING. If concern is still present, clear DTCs and retest system. If DTCs 
reset, perform COMPUVALVE CHECK under QUICK TEST. If fault still exists, replace compuvalve. 

5) Check HO2S Voltage Activity 
 
Turn ignition off. Disconnect in-line 10-pin harness connector C422. Place ALT fuel switch in GAS 
position. Start engine and allow to idle. Ensure engine is at normal operating temperature. Using DVOM, 
measure voltage between in-line harness connector C422F terminal "C" (Gray/Red wire), and terminals 
"A" (Gray/Light Blue wire) and "B" (Red/Black wire). See 

Fig. 15

 . Compare voltage measurements to 

specification in HO2S SENSOR OPERATING VOLTAGE SPECIFICATIONS table. If both 
voltages are within specification, go to next step. If either voltage is not within specification, go to step 
7) . 

6) Check HO2S Circuits To Compuvalve 
Turn ignition off. Disconnect bi-fuel relay module power supply harness connector C495. Disconnect 
compuvalve harness connector C1294. Perform the following: 

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Using DVOM, measure resistance between chassis ground and in-line harness connector C422M 
terminals "A", "B" and "C". See Fig. 15 .  

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Using DVOM, measure resistance between in-line harness connector C422M terminal "A" and 
compuvalve harness connector C1294 terminal No. 30. See Fig. 7 and Fig. 15 .  

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Using DVOM, measure resistance between in-line harness connector C422M terminal "B" and 
compuvalve harness connector C1294 terminal No. 10. See Fig. 7 and Fig. 15 .  

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Using DVOM, measure resistance between in-line harness connector C422M terminal "C" and 
compuvalve harness connector C1294 terminal No. 21 and 32. See Fig. 7 and Fig. 15 .  

If all resistances are more than 10 k/ohms between in-line harness connector C422M and chassis ground, 
and are less than 5 ohms between connectors C422M and C1294, go to next step. If any resistance 
measurement is 10 k/ohms or less between connector C422M and chassis ground, or 5 ohms or more 
between connectors C422M and C1294, repair open or short to ground in affected circuit. See ENGINE 
PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. 

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

  

7) Check HO2S Circuits To Sensors 
Ensure in-line harness connector C422 is disconnected. Disconnect in-line harness connectors C133, 
C139, C431 and C432. For connector location, see CONNECTOR LOCATIONS under CONNECTOR 
IDENTIFICATION & LOCATION. Perform the following: 

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Using DVOM, measure resistance between chassis ground and in-line harness connector C422F 
terminals "A", "B" and "C". See Fig. 15 .  

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Using DVOM, measure resistance of Gray/Light Blue wire between in-line harness connector 
C422F terminal "A" and in-line harness connector C139M terminal No. 13. See Fig. 15 and Fig. 
21 .  

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Using DVOM, measure resistance of Red/Black wire between in-line harness connector C422F 
terminal "B" and in-line harness connector C139M terminal No. 14. See Fig. 15 and Fig. 21 .  

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Using DVOM, measure resistance of Gray/Red wire between in-line harness connector C422F 
terminal "C" and in-line harness connector C133M terminal No. 18. See Fig. 15 and Fig. 19 .  

If all resistances are more than 10 k/ohms between connector C422F and chassis ground, and less than 5 
ohms between connectors C133M, C139M and C422F, replace appropriate HO2S. If any resistance 
measurement is 10 k/ohms or less between connector C422F and chassis ground, or 5 ohms or more 
between connectors C133M, C139M and C422F, repair open or short to ground in affected circuit. See 
ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. 

TEST HC: FUEL DELIVERY SYSTEM 

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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Chassis components.  

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Engine vacuum.  

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Fuel pressure.  

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Fuel filter.  

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Fuel supply.  

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Fuel injector.  

System Inspection 

Perform SYSTEM INSPECTION before proceeding with TESTING. Check the following:  

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Mechanical Inspection 

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