Ford F150 Pickup. Instruction - part 1622

Keep Alive Memory (KAM) in tables that are referenced by engine speed and load (and by bank for engines 
with two HO2S sensors forward of the catalyst). Learning the corrections in KAM improves both open loop and 
closed loop air/fuel ratio control. Advantages include:  

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Short term fuel trim does not have to generate new corrections each time the engine goes into closed loop. 

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Long term fuel trim corrections can be used both while in open loop and closed loop modes.  

Long term fuel trim is represented as a percentage, just like short term fuel trim, however it is not a single 
parameter. There is a separate long term fuel trim value that is used for each RPM/load point of engine 
operation. Long term fuel trim corrections may change depending on the operating conditions of the engine 
(RPM and load), ambient air temperature and fuel quality (percent alcohol, oxygenates, etc.). When viewing the 
LONGFT1/2 PID(s), the values may change a great deal as the engine is operated at different RPM and load 
points. The LONGFT1/2 PID(s) will display the long term fuel trim correction that is currently being used at 
that RPM/load point. 

As fuel control and air metering components age and vary from nominal values, fuel trim learns corrections 
while in closed loop fuel control. Corrections are stored in a table that is a function of engine speed and load. 
Tables reside in Keep Alive Random Access Memory (RAM) and are used to correct fuel delivery during open 
and closed loop. As changing conditions continue, individual cells are allowed to update for that speed load 
point. If both Short Term FT and Long Term FT reach their high or low limit and can no longer compensate 
during adaptive process, MIL is illuminated and a DTC is stored. Whenever a fuel injector or fuel pressure 
regulator is replaced, RAM should be cleared. This is necessary so PCM does not use previously learned fuel 
trim values. To clear RAM, see KEEP ALIVE RANDOM ACCESS MEMORY RESET PROCEDURE 
under CLEARING CODES under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - CNG, FLEX-
FUEL & GASOLINE article. 

Idle Air Trim 

Idle Air Trim is designed to adjust Idle Air Control (IAC) calibration to correct for wear and aging of 
components. When engine conditions meet learning requirement, the strategy monitors the engine and 
determines the values required for ideal idle calibration. Idle air trim values are stored in a table for reference. 
This table is used by PCM as a correction factor when controlling idle speed. The table is stored in Keep Alive 
Random Access Memory (RAM) and retains the learned values even after engine is shut off. A DTC is output if 
idle air trim has reached its learning limits. 

Whenever an IAC component is replaced or cleaned or a service affecting idle is performed, it is recommended 
that RAM be cleared. This is necessary so idle strategy does not use previously learned idle air trim values. To 
clear RAM, see KEEP ALIVE RANDOM ACCESS MEMORY RESET PROCEDURE under CLEARING 
CODES under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - CNG, FLEX-FUEL & GASOLINE 
article. It is important to note that erasing DTCs with a scan tool does not reset idle air trim table. Once RAM 
has been reset, engine must idle for 15 minutes (actual time varies between strategies) to learn new idle air trim 
values. Idle quality will improve as strategy adapts. Adaptation occurs in 4 separate modes. The modes are 
shown in IDLE AIR TRIM LEARNING MODES table. 

IDLE AIR TRIM LEARNING MODES 

Transaxle/Transmission Range

Air Conditioning Mode

Neutral

A/C On

 

2003 Ford Pickup F150 

2003 ENGINE PERFORMANCE Theory & Operation - CNG, Flex-Fuel & Gasoline

  

Idle Speed Control Closed Throttle Determination 

One of the fundamental criteria for entering RPM control is an indication of closed throttle. Throttle mode is 
always calculated to the lowest learned throttle position voltage seen since engine start. This lowest learned 
value is called "ratch", since the software acts like a one-way ratch. The ratch value (voltage) is displayed as 
TPREL PID. The ratch value is relearned after every engine start. Ratch will learn the lowest steady TP voltage 
seen after engine starts. In some cases, ratch can learn higher values of TP. The time to learn higher values is 
significantly longer than the time to learn lower values. The brakes must also be applied to learn the higher 
values. 

All PCM functions are done using this ratch voltage, including idle speed control. PCM goes into closed throttle 
mode when TP voltage is at ratch (TPREL PID) value. Increase in TP voltage, normally less than 0.05 volt, will 
put PCM in part throttle mode. Throttle mode can be viewed by looking at TP MODE PID. With throttle closed, 
PID must read C/T (closed throttle). Slightly corrupt values of ratch can prevent PCM from entering closed 
throttle mode. An incorrect part throttle indication at idle will prevent entry into closed throttle RPM control, 
and could result in a high idle. Ratch can be corrupted by a Throttle Position (TP) sensor or circuit that "drops 
out" or is noisy, or by loose/worn throttle plates that close tight during a decel and spring back at a normal 
engine vacuum. 

Multiplexing 

The increased number of modules on the vehicle necessitates a more efficient method of communication. 
Multiplexing is a method of designating a system for sending two or more signals simultaneously over a single 
circuit. In an automotive application, multiplexing is used to allow two or more electronic modules to 
communicate simultaneously over a single media. Typically this media is a twisted pair of wires. The 
information or messages that can be communicated on these wires consists of commands, status or data. The 
advantage of using multiplexing is to reduce the weight of the vehicle by reducing the number of redundant 
components and electrical wiring. 

Multiplexing Implementation 

Currently Ford Motor Company uses two different types of communication language protocols to communicate 
with the Powertrain Control Module (PCM). These protocols are Standard Corporate Protocol (SCP) and 
Controller Area Network (CAN). Starting with the 2003 model year, Ford will phase-in High Speed-CAN (HS-
CAN) for PCM communication with the following vehicles:  

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LS  

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Thunderbird  

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Focus 2.3L Partial Zero Emission Vehicle (PZEV)  

The LS and Thunderbird will use HS-CAN between the Data Communication Link (DCL) connector and the 
PCM for scan tool to PCM diagnostics only. Inter communication (PCM to other network modules) for the LS 

Neutral

A/C Off

Drive

A/C On

Drive

A/C Off

 

2003 Ford Pickup F150 

2003 ENGINE PERFORMANCE Theory & Operation - CNG, Flex-Fuel & Gasoline

  

and Thunderbird will continue to use SCP. The Focus 2.3L PZEV will use HS-CAN for PCM and instrument 
cluster (IC) module communication and for scan tool diagnostics. 

All other vehicles for model year 2003 will continue to use SCP as its communication media for the PCM. 

Standard Corporate Protocol 

SCP is a communication language protocol based on SAE J1850 and is used by Ford Motor Company for 
exchanging bi-directional message (signals) between electronic modules. Two or more signals can be sent over 
one SCP network circuit. Fords SCP network operates at 41.6 kB/sec. 

Included in these messages is diagnostic data that is outputted over the BUS (+) and BUS (-) lines to the Data 
Link Connector (DLC). PCM connection to the DLC is typically done with a two wire, twisted pair cable used 
for network interconnection. The diagnostic data such as Self-Test or PIDs can be accessed with a scan tool. 

High Speed - Controller Area Network (HS-CAN) 

HS-CAN is based on SAE J2284, ISO-11898 and is a serial communication language protocol used to transfer 
messages (signals) between electronic modules or nodes. Two or more signals can be sent over one CAN 
network circuit allowing two or more electronic modules or nodes to communicate with each other. This 
communication or multiplexing network operates at 500 kB/sec and allows the electronic modules to share their 
information messages. 

Included in these messages is diagnostic data that is outputted over the CAN High (+) and CAN Low (-) lines to 
the Data Link Connector (DLC). PCM connection to the DLC is typically done with a two wire, twisted pair 
cable used for the network interconnection. The diagnostic data such as Self-test or PIDs can be accessed with a 
scan tool. 

DIAGNOSTIC MONITORS 

Starting with 2002 model year, all California passenger cars and trucks (up to 14,000 lbs. GVW) and all federal 
passenger cars and trucks (up to 8500 lbs. GVW) are required to comply with either CARB-OBD-II or EPA 
OBD requirements. Federal heavy-duty truck up to 10,000 lbs. GVWR choosing to certify using Light Duty 
Truck provisions must comply with OBD-II requirements. Federal heavy-duty trucks over 8500 lbs. GVW are 
not required to comply with any OBD regulation, however in order to meet minimum serviceability 
requirements, must comply with OBD-I requirements. OBD-II requirements apply to gasoline vehicles, diesel 
vehicles, ethanol flexible fuel vehicles and bi-fuel CNG/LPG vehicles while running on gasoline. OBD-II 
requirements are being phased in on dedicated NGVs and bi-fuel CNG/LPG vehicles while running on gaseous 
fuels. Passenger cars and trucks sold in Canada and Mexico have Federal calibrations, unless unique 
calibrations are certified for Mexico at high altitude. 

OBD-II system monitors virtually all emission control systems and components that can affect tailpipe or 
evaporative emissions. In most cases, malfunctions must be detected before emissions exceed 1.5 times the 
applicable 50-100 k/mile emission standards. If a system or component exceeds emission thresholds or fails to 
operate within a manufacturer's specifications, a DTC will be stored and MIL will be illuminated within 2 
driving cycles. OBD-II system monitors for malfunctions either continuously, regardless of driving mode, or 
non-continuous, once per drive cycle during specific drive modes. A pending DTC is stored in PCM Keep Alive 

 

2003 Ford Pickup F150 

2003 ENGINE PERFORMANCE Theory & Operation - CNG, Flex-Fuel & Gasoline

  

Memory (KAM) when a malfunction is initially detected. This pending DTC may be erased on the third vehicle 
restart after 2 consecutive drives cycles with no malfunction. However, if malfunction is still present after 2 
consecutive drive cycles, MIL is illuminated. Once MIL is illuminated, 3 consecutive drive cycles without a 
malfunction detected are required to extinguish MIL. DTC is erased after 40 engine warm-up cycles once MIL 
is extinguished. 

In addition to specifying and standardizing much of the diagnostics and MIL operation, OBD-II requires the use 
of a standard Diagnostic Link Connector (DLC), standard communication links and messages, standardized 
DTCs and terminology. Examples of standard diagnostic information are freeze frame data and Inspection 
Maintenance (IM) readiness indicators. Freeze frame data describes data stored in KAM at the point the 
malfunction is initially detected. Freeze frame data consists of parameters such as engine RPM and load, state 
of fuel control, spark, and warm-up status. Freeze frame data is stored at the time the first malfunction is 
detected, however, previously stored conditions will be replaced if a fuel or misfire fault is detected. This data is 
accessible with scan tool to assist in repairing vehicle. OBD IM readiness indicators show whether all of the 
OBD monitors have been completed since last time KAM or PCM DTC(s) have been cleared. A DTC P1000 is 
also stored to indicate that some monitors have not completed. In some states, it may be necessary to perform an 
OBD check in order to renew a vehicle registration. The IM readiness indicators must show that all monitors 
have been completed prior to OBD check. DIAGNOSTIC MONITORING TESTS provides a general 
description of each OBD-II monitor. In these descriptions, monitor strategy, hardware, testing requirements and 
methods are presented to provide an overall understanding of monitor operation. For a description of diagnostic 
monitors, see DIAGNOSTIC MONITORS in SELF-DIAGNOSTICS - CNG, FLEX-FUEL & GASOLINE 
article. 

CONSTANT CONTROL RELAY MODULE 

Constant Control Relay Module (CCRM) provides vehicle power to powertrain control module and electronic 
system. CCRM controls cooling fan and A/C clutch. CCRM also contains Fuel Pump Driver Module (FPDM) 
power supply relay, which supplies power to FPDM. If any of the internal components of CCRM fail, entire 
unit must be replaced. For location of CCRM, see CONSTANT CONTROL RELAY MODULE 
LOCATION table. 

CONSTANT CONTROL RELAY MODULE LOCATION 

FUEL PUMP DRIVER MODULE 

FPDM receives a duty-cycle signal from PCM and controls fuel pump operation in relation to this duty cycle. 
This results in variable fuel pump operation speed. The FPDM sends diagnostic information to PCM on fuel 

Application

Location

Mustang

Mounted On Bracket, Behind Engine Coolant Reservoir

ZX2

In Left Front Of Engine Compartment

NOTE:

On LS and Thunderbird, Fuel Pump Driver Module (FPDM) functions are 
incorporated into Rear Electronic Module (REM). Fuel pump operation is same 
as applications using the stand-alone FPDM. REM will communicate diagnostic 
information through BUS (+) and BUS (-) circuits instead of using a fuel pump 
monitor circuit.

 

2003 Ford Pickup F150 

2003 ENGINE PERFORMANCE Theory & Operation - CNG, Flex-Fuel & Gasoline