Ford F150 Pickup. Instruction - part 1504

Disconnect HO2S connector. Connect DVOM between HO2S SIG and SIG RTN circuits at HO2S 
harness connector. Disconnect any vacuum hose from vacuum tree. Start engine and operate at 2000 
RPM. If DVOM voltage is less than .4 volt within 30 seconds, reconnect vacuum hose and reconnect all 
connectors. Go to next step. If DVOM voltage is .4 volt or more after 30 seconds, replace HO2S. 

77) Monitor HO2S PID For Proper Switching 
Connect scan tool to Data Link Connector (DLC). Start engine and allow to idle. Ensure engine is at 
normal operating temperature. Using scan tool, access HO2S PID for DTC retrieved. Observe HO2S PID 
voltage while wiggling and bending small sections of wiring harness from HO2S to PCM. If HO2S PID 
voltage stays high (more than .45 volt) or stays low (less than .45 volt), isolate cause of lack of HO2S 
switches. Repair as necessary. If HO2S PID voltage switches, go to next step. 

78) Test Drive While Monitoring HO2S PID For Proper Switching 
 
Using an assistant, test drive vehicle under various conditions while assistant observes suspect HO2S 
PID. If suspect HO2S PID voltage switches properly, system is okay at this time and testing is complete. 
If voltage does not switch properly, replace HO2S. 

90) For KOER Only DTC P1127 
DTC P1127 indicates that downstream HO2S heaters were not cycled on during KOER self-test due to 
exhaust temperatures falling below a minimum calibrated value. Possible causes are: 

z

Engine Not At Operating Temperature.  

z

Exhaust System Too Cool.  

Connect scan tool to Data Link Connector (DLC). Using scan tool, access HO2S HTR-11 & HO2S HTR-
21 PIDs from PID/DATA MONITOR & RECORD menu. If both HO2S HTR PIDs indicate ON, perform 
KOER ON-DEMAND SELF-TEST while engine is still running to verify P1127 is no longer present. If 
either HO2S HTR PID indicates OFF, operate engine until all HO2S HTR PIDs indicate ON. Repeat 
KOER ON-DEMAND SELF-TEST. 

100) For KOER Only DTCs P0040, P0041, P1128 & P1129 
These DTCs indicate that during KOER self-test, HO2S signal response for a fuel shift corresponded to 
incorrect bank (cross between banks). DTC P1128 refers to upstream HO2S-11 or HO2S-21. DTC P1129 

NOTE:

HO2S PID may be displayed on scan tool as O2S.

NOTE:

A break in step numbering sequence occurs at this point. Procedure skips 
from step 78) to step 90). No test procedures have been omitted.

NOTE:

For additional testing information, see DIAGNOSTIC AIDS.

NOTE:

A break in step numbering sequence occurs at this point. Procedure skips 
from step 90) to step 100). No test procedures have been omitted.

NOTE:

For additional testing information, see DIAGNOSTIC AIDS.

 

2003 Ford Pickup F150 

2003 ENGINE PERFORMANCE Self-Diagnostics - CNG, Flex-Fuel & Gasoline

  

refers to downstream HO2S-12 or HO2S-22. Possible causes for these faults are: 

z

Crossed HO2S Connectors  

z

Crossed HO2S Wiring At HO2S Connector  

z

Crossed HO2S Wiring At PCM Connector  

Turn ignition switch to OFF position. Disconnect suspect HO2S harness connector. Inspect connector for 
indication of crossed or stretched wires or wire harnesses incorrectly installed. Repair as necessary. If no 
faults are found, go to next step. 

101) Verify Proper HO2S SIG Terminal Location 
 
Disconnect PCM connector. Inspect connector for loose, damaged or corroded terminals. Repair as 
necessary. Disconnect both suspect HO2S harness connectors. HO2S DTC identification is as follows: 

z

DTC P1128 is for upstream HO2S-11 and HO2S-21.  

z

DTC P1129 is for downstream HO2S-12 and HO2S-22.  

Refer to illustrations for HO2S identification. See Fig. 230-Fig. 232 . Using a DVOM, measure resistance 
of HO2S SIG circuit between suspect HO2S harness connector and PCM harness connector. See NGV 
HO2S PCM TERMINAL IDENTIFICATION table. See PCM CONNECTOR IDENTIFICATION 
and Fig. 233. If resistance is less than 5 ohms, HO2S SIG circuit is okay. Fault is intermittent and cannot 
be duplicated at this time. If resistance is 5 ohms or more, HO2S wiring is crossed. Recheck all HO2S 
wiring terminal locations at PCM and HO2S connectors. Repair as necessary. 

TEST HB: NATURAL GAS FUEL DELIVERY SYSTEM 

Diagnostic Aids 

Perform this test when directed by QUICK TEST or if directed by other test procedures. This test is used to 
diagnose:  

z

Fuel Pressure  

z

Fuel Supply Lines  

z

Fuel Filter  

z

Fuel Injector(s)  

z

Fuel Pressure Regulator  

z

Fuel Injection Supply Manifold (Fuel Rail)  

z

Fuel Rail Solenoid Shutoff Valve(s)  

NOTE:

After each service or repair procedure has been completed, reconnect all 
components. Clear DTCs and repeat QUICK TEST procedures to ensure all EEC-
V systems are working properly and DTCs are no longer present.

NOTE:

Fuel rail solenoid shutoff valve is also referred to as low pressure solenoid 

 

2003 Ford Pickup F150 

2003 ENGINE PERFORMANCE Self-Diagnostics - CNG, Flex-Fuel & Gasoline

  

Fig. 237: Identifying Natural Gas Vehicle Fuel System Components (Crown Victoria) 
Courtesy of FORD MOTOR CO 

shutoff valve. Fuel tank solenoid shutoff valve is also referred to as fuel tank 
solenoid valve.

 

2003 Ford Pickup F150 

2003 ENGINE PERFORMANCE Self-Diagnostics - CNG, Flex-Fuel & Gasoline

  

Fig. 238: Identifying Natural Gas Vehicle Fuel System Components (Econoline & Pickup) 
Courtesy of FORD MOTOR CO 

Testing 

1) Check System Integrity 
Turn ignition switch to ON position for 5 seconds. Turn ignition switch to OFF position. Inspect fuel 
system for leaks, damaged or kinked hoses. See Fig. 237 or Fig. 238 . Inspect wiring harness for damage 
or loose connectors. Ensure vehicle has followed maintenance schedule. Ensure the following conditions 
are met: 

z

Fuel Filter Element Is Okay  

z

Inertia Fuel Shutoff (IFS) Is Set  

z

Battery Is Fully Charged  

z

Fuel System Fuses Are Okay  

WARNING:

Always refer to safety procedures to reduce possibility of injury. See 
FUEL SYSTEM SAFETY PRECAUTIONS.

 

2003 Ford Pickup F150 

2003 ENGINE PERFORMANCE Self-Diagnostics - CNG, Flex-Fuel & Gasoline