Ford F150 Pickup. Instruction - part 1403

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Select VEHICLE & ENGINE SELECTION menu.  

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Select NEW VEHICLE, YEAR & MODEL.  

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Follow operating instructions from scan tool menu.  

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Select GENERIC OBD-II FUNCTIONS. Press CONT button if OBD-II monitors are not complete.  

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Turn ignition switch to ON position.  

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Select FREEZE FRAME PID TESTS.  

DIAGNOSING ADAPTIVE FUEL DTCS 

Description 

Adaptive fuel DTCs diagnostic techniques help isolate root causes of adaptive fuel concerns. Before 
proceeding, road test vehicle to verify if any driveability concerns are present. These diagnostic aids are meant 
as a supplement to system test steps under SYSTEM TESTS. For a description of fuel trim, see FUEL TRIM 
under POWERTRAIN CONTROL MODULE SOFTWARE under COMPUTERIZED ENGINE CONTROLS 
in THEORY & OPERATION - CNG, FLEX-FUEL & GASOLINE article. 

Obtain Freeze Frame Data 

Freeze Frame Data can be helpful in duplicating and diagnosing adaptive fuel concerns. This data (a snapshot of 
certain PID values, recorded at time DTC was stored in Continuous Memory) is helpful to determine how 
vehicle was being driven when fault occurred, and can be especially useful on intermittent concerns. Freeze 
Frame Data, in many cases, can help to isolate possible areas of concern as well as rule out others. See 
FREEZE FRAME DATA MODE for a more detailed description of this data. 

Using LONGFT1 & LONGFT2 (Dual Bank Engines) PIDs 

LONGFT1 or LONGFT2 PIDs can be useful for diagnosing fuel trim concerns. A negative PID value indicates 
that fuel is being reduced to compensate for a rich condition, while a positive PID value indicates that fuel is 
being increased to compensate for a lean condition. It is important to know that there is a separate LONGFT 
value that is used for each RPM/load point of engine operation. When viewing LONGFT1 or LONGFT2 PIDs, 
values may change a great deal as engine is operated at different RPM and load points. This is because fuel 
system may have learned corrections for fuel delivery concerns that can change as a function of engine RPM 
and load. LONGFT1 or LONGFT2 PIDs will display fuel trim currently being used at that RPM and load point. 
Observing these changes in LONGFT1 or LONGFT2 PIDS can help when diagnosing fuel system concerns. 
For example:  

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A contaminated MAF sensor would result in matching LONGFT1 and LONGFT2 correction values that 
are negative at idle (reducing fuel), but positive (adding fuel) at higher RPM and loads.  

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LONGFT1 values that differ greatly from LONGFT2 values would rule out concerns that are common for 
both banks (for example, fuel pressure concerns, MAF sensor, etc. could be ruled out).  

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Vacuum leaks would result in large rich corrections (positive LONGFT1 and LONGFT2 value) at idle, 
but little or no correction at higher RPM and loads.  

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A plugged fuel filter will result in no correction at idle, but large rich corrections (positive LONGFT1 or 
LONGFT2 value) at high RPM and load. 

 

2003 Ford Pickup F150 

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

  

Resetting Long Term Fuel Trims 

Long term fuel trim corrections can be reset by resetting PCM Keep Alive Memory (KAM). See KEEP ALIVE 
RANDOM ACCESS MEMORY RESET PROCEDURE under CLEARING CODES under SELF-
DIAGNOSTIC SYSTEM. After making a fuel system repair, KAM must be reset. For example, if dirty/plugged 
injectors cause engine to run lean and generate rich long term corrections, replacing injectors and not resetting 
KAM will now make engine run very rich. The rich correction will eventually be "Learned Out" during closed 
loop operation, but vehicle may have poor driveability and have high CO emissions while it is learning. 

DTC P0171/P0174 System Too Lean Diagnostic Aids 

The ability to identify the type of lean condition causing the concern can be crucial to a correct diagnosis. The 
following are possible causes:  

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Air Measurement System 
 
With this condition, engine may actually run rich or lean of stoichiometric (14.7:1 air/fuel ratio), if 
Powertrain Control Module (PCM) is not able to compensate enough to correct for condition. One 
possibility is that the mass of air entering engine is actually more than what MAF sensor is indicating to 
PCM. Examples; with a contaminated MAF sensor, engine would run lean at higher RPM because PCM 
would deliver fuel for less air than is actually entering engine. Examples are as follows; inaccurate MAF 
sensor measurement can be caused by a corroded connector, contaminated or dirty MAF. A contaminated 
MAF sensor will typically result in a rich system at low airflow resulting in PCM reducing fuel, and a 
lean system at high airflow resulting in PCM increasing fuel, etc. 

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Vacuum Leaks/Unmetered Air 
 
With this condition, engine may actually run lean of stoichiometric (14.7:1 air/fuel ratio), if PCM is not 
able to compensate enough to correct for condition. This condition can be caused by unmetered air 
entering engine, or due to a MAF malfunction. Volume of air entering engine is actually more than what 
MAF sensor is indicating to PCM. Vacuum leaks will normally be most apparent when high manifold 
vacuum is present (for example, during idle or light throttle). If freeze frame data indicates that fault 
occurred at idle, a check for vacuum leaks/unmetered air might be the best starting point. Examples of 
this are: loose, leaking or disconnected vacuum lines, intake manifold gaskets or "O" rings, throttle body 
gaskets, brake booster, air inlet tube, stuck/frozen/aftermarket PCV valve or an unseated engine oil 
dipstick, etc. 

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Insufficient Fueling 
 
With this condition, engine may actually run lean of stoichiometric (14.7:1 air/fuel ratio), if PCM is not 
able to compensate enough to correct for condition. This condition can be caused by a fuel delivery 
system concern that restricts or limits amount of fuel being delivered to engine. This condition will 
normally be most apparent when engine is under a heavy load and at high RPM, when a higher volume of 
fuel is required. If freeze frame data indicates that fault occurred under a heavy load and at higher RPM, a 

NOTE:

If system is lean at certain conditions, then LONGFT PID would be a positive 
value at those conditions, indicating that increased fuel is needed.

 

2003 Ford Pickup F150 

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

  

check of fuel delivery system, such as checking fuel pressure with engine under a load might be the best 
starting point. Examples of this are: low fuel pressure (fuel pump, fuel filter, fuel leaks, restricted fuel 
supply lines), fuel injector concerns, etc. 

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Exhaust System Leaks 
 
In this type of condition, engine may actually be running rich of stoichiometric (14.7:1 air/fuel ratio), 
because fuel control system is adding fuel to compensate for a perceived lean condition. This condition is 
caused by oxygen entering exhaust system from an external source. The HO2S will react to this exhaust 
leak by increasing fuel delivery. This condition will cause exhaust gas mixture from cylinder to be rich. 
Examples of this are: exhaust system leaks upstream or near HO2S, poorly welded/leaking HO2S boss or 
malfunctioning secondary air injection system, etc.  

DTC P0172/P0175 System Too Rich Diagnostic Aids 

System rich concerns are usually caused by fuel system concerns, although MAF sensor, and base engine (for 
example, engine oil contaminated with fuel) should also be checked. The following are possible causes:  

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Air Measurement System 
 
With this condition, engine may actually run rich or lean of stoichiometric (14.7:1 air/fuel ratio), if PCM 
is not able to compensate enough to correct for condition. One possibility is that the mass of air entering 
engine is actually less than what MAF sensor is indicating to PCM. For example, with a contaminated 
MAF sensor, engine would run rich at idle because PCM would deliver fuel for more air than is actually 
entering engine. Examples of this are; inaccurate MAF sensor measurement can be caused by a corroded 
connector, contaminated or dirty MAF. A contaminated MAF sensor will typically result in a rich system 
at low airflow resulting in PCM reducing fuel, and a lean system at high airflow results in PCM 
increasing fuel. 

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Fuel System 
 
With this condition, the engine may actually run rich of stoichiometric (14.7:1 air/fuel ratio), if PCM is 
not able to compensate enough to correct for condition. This situation can be caused by a fuel delivery 
system that is delivering excessive fuel to engine. Examples of this are: 

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Fuel pressure regulator causes excessive fuel pressure (system rich at all airflow), fuel pressure can 
be intermittent, going to pump deadhead pressure, then returning to normal after engine is turned 
off, then restarted.  

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Fuel pressure regulator vacuum hose off (causes excessive fuel pressure at idle, system rich at idle 
airflow). Fuel pressure regulator diaphragm ruptured (fuel leaking into intake manifold, system rich 
at lower airflow).  

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Fuel return line crimped/damaged (fuel pressure high, system rich at lower airflow).  

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Fuel injector leaks (injector delivers extra fuel).  

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EVAP canister purge valve leak (if canister is full of vapors, introduces extra fuel). 

NOTE:

If system is rich at certain conditions, then LONGFT PID would be a negative 
value at that airflow, indicating that decreased fuel is needed.

 

2003 Ford Pickup F150 

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

  

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Fuel rail pressure sensor (electronic returnless fuel systems) concern causes sensor to indicate 
lower pressure than actual. PCM commands higher pressure to Fuel Pump Driver Module (FPDM), 
causing high fuel pressure (system rich at all airflow).  

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Base Engine 
 
Engine oil contaminated with fuel can contribute to a rich running engine.  

OUTPUT TEST MODE 

Description 

This mode allows a technician to energize and de-energize most of the system output actuators on command. 
After accessing OUTPUT TEST MODE, outputs and cooling fans can be turned on and off separately. OTM 
will turn off after vehicle is started or after cycling ignition switch off then on. 

Accessing Output Test Mode 

To access OUTPUT TEST MODE, turn ignition switch to OFF position. Ensure test equipment is properly 
attached. Program scan tool using the following steps:  

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Select VEHICLE & ENGINE SELECTION menu.  

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Select NEW VEHICLE, YEAR & MODEL.  

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Follow operating instructions from scan tool menu.  

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Select DIAGNOSTIC DATA LINK.  

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Select POWERTRAIN CONTROL MODULE.  

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Select DIAGNOSTIC TEST MODE.  

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Select ACTIVE COMMAND MODE.  

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Select OUTPUT TEST MODE.  

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Turn ignition switch to ON position.  

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Follow operating instructions from scan tool menu.  

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Select START to turn outputs on.  

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Select STOP to turn outputs off.  

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Select either LOW SPEED FAN, HIGH SPEED FAN or ALL ON mode. 

WARNING:

When all outputs are on, the electric fuel pump is briefly energized, 
ensure fuel system is intact and is not being serviced. When low or high 
speed fan control(s) are actuated, ensure fan blades are clear of 
obstructions.

NOTE:

OUTPUT TEST MODE will default outputs to off after 10 minutes, and fuel pump 
to off after 7-10 seconds.

 

2003 Ford Pickup F150 

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