Engine Controls - Theory & Operation - Gasoline & Ngv Ford Explorer Sport Trac I

INTRODUCTION

Note. Information for Escort applies to Escort ZX2 unless otherwise indicated. For Mercury Villager information, see THEORY & OPERATION - VILLAGER article.

This article covers basic description and operation of engine performance related systems and components. Read this article before diagnosing vehicles or systems with which you are not completely familiar. To identify vehicles and engines, see appropriate INTRODUCTION article.

Idle Air Control Valve Assembly

Idle Air Control (IAC) valve assembly is used to control idle speed and provide a dashpot function. IAC valve assembly meters inlet air around the throttle plate through a by-pass within the IAC valve assembly and throttle body. (Scheme 1)- (Scheme 3).

The Powertrain Control Module (PCM) determines desired idle speed or air by-pass and signals the IAC valve assembly through specified duty cycle. The IAC solenoid is built into IAC valve assembly. IAC solenoid responds by positioning the IAC valve to control amount of air by-passed. PCM monitors engine speed and adjusts IAC duty cycle to achieve desired RPM. IAC valve assembly is not adjustable and cannot be cleaned.

On applications with air assisted injectors, IAC valve supplies a small jet of air into path of fuel injectors, creating an increase in fuel atomization at low speed and light load conditions. (Scheme 2)

Scheme 1

Scheme 2

Scheme 3

Supercharger Assembly

Supercharger assembly is a positive displacement pump designed to supply an excess volume of intake air to engine by increasing air pressure and density in the intake manifold. Supercharger assembly incorporates a by-pass system to reduce air handling losses when boost is not required, resulting in better fuel economy. (Scheme 4) Supercharger can increase torque across entire engine operating range from 25-50 percent without compromising driveability or emissions.

Supercharger is matched to engine by its displacement and belt ratio, and can provide excess airflow at any engine speed. Drive gears for supercharger are pressed into place and are not serviceable. Supercharger must be replaced as a unit. Supercharger contains 2 belt driven 3-lobed helical cut rotors which are supported by ball bearings in front and needle bearings at the rear. The rotors helical shape and internal specialized porting provide a smooth discharge flow and low noise levels during operation.

Scheme 4

Supercharger By-Pass System

Supercharger By-Pass (SCB) system allows high pressure air at outlet of supercharger to vent back to inlet side of supercharger. This equalizes pressure and eliminates boost for times when supercharger function is not required. Descriptions of supercharger by-pass system components are as follows

1. Vacuum By-Pass Actuator During normal operation engine vacuum is applied to upper port of vacuum by-pass actuator. Lower port of vacuum by-pass actuator references air pressure in clean air tube, cancelling out any pressure difference in intake air system. Actuator opens during engine high vacuum conditions (by-passing supercharger). As throttle is opened and engine vacuum decreases, vacuum by-pass actuator closes to allow supercharger to pressurize air in intake manifold.
2. SCB Solenoid/Thermactor Air Control Solenoid SCB solenoid is used to control intake manifold vacuum to vacuum by-pass actuator. The SCB solenoid is de-energized during normal operating conditions. The Powertrain Control Module (PCM) will transmit an output signal to activate SCB solenoid to apply stored vacuum from vacuum reservoir assembly to vacuum by-pass actuator when an undesirable condition occurs in the engine. Once engine condition is corrected, SCB solenoid will be deactivated by PCM allowing engine intake manifold vacuum to control vacuum by-pass actuator.
3. Vacuum Reservoir Assembly Vacuum reservoir assembly stores vacuum that is applied to the vacuum actuator when a condition such as overheating or critical sensor failure is generated.

Supercharger Intercooler (Charge Air Cooler) System

Intercooler system is designed to cool induction air which has been heated by the supercharger. Removing heat from pressurized air through an intercooler increases air density, which results in increased combustion efficiency, engine horsepower and torque.

Intercooler system consists of the following components: an additional radiator and coolant reservoir (independent from engine cooling system), an intercooler (charge air cooler) located in lower intake manifold and a charge air cooler pump (electric water pump) located at right front side of engine compartment and intercooler coolant hoses. (Scheme 5)

Charge air cooler pump is controlled by PCM and charge air cooler pump relay to maintain a desirable intake air temperature signalled by a second intake air temperature sensor (IAT2) located in lower intake manifold.

Scheme 5

Intake Manifold Runner Control - 2.0L (VIN P), 2.5L (VIN L), Windstar 3.8L (VIN 4), & 4.2L (VIN 2)

On 2.5L, 3.8L & 4.2L engines, Intake Manifold Runner Control (IMRC) system consists of a remote mounted electric actuator with an attaching cable or linkage to operate the housing butterfly valve plate levers located between intake manifold and cylinder head(s). (Scheme 6)- (Scheme 10). On 2.0L, IMRC uses a motorized actuator mounted directly to a single housing, between intake manifold and cylinder head, without use of a cable or linkage. PCM uses a positive change in Throttle Position (TP) sensor along with the increase in engine RPM from Crankshaft Position (CKP) sensor to open butterfly valve plates.

IMRC housing is an aluminum casting with 2 intake air passages for each cylinder. One passage is always open and the other is opened and closed with a butterfly valve plate(s). IMRC housing uses a return spring to hold butterfly valve plate(s) in closed position. Electric actuator houses an internal switch or switches, dependent on application, to provide feedback to PCM indicating butterfly valve plate(s) position.

When engine speed is less than 3000 RPM, electric actuator will not be energized, allowing IMRC butterfly valve plate(s) to remain in closed position. When engine speed is approximately 3000 RPM or more, electric actuator is energized, causing butterfly valve plate(s) to the open position to improve high speed engine performance. Some applications will activate IMRC butterfly valve plate(s) when engine speed is about 1500 RPM.

Scheme 6

Scheme 7

Scheme 8

Scheme 9

Scheme 10

Intake Manifold Swirl Control Vacuum Actuated System - 2.3L (VIN D)

Intake Manifold Swirl Control (IMSC) vacuum actuated system consists of manifold mounted vacuum actuator and Powertrain Control Module (PCM) controlled electric solenoid. (Scheme 11)and (Scheme 12). PCM monitors Throttle Position (TP) sensor, cylinder head temperature sensor and crankshaft position sensor signals to determine activation of IMSC. A positive change in voltage from TP sensor along with increase in RPM at proper engine temperature must be present to open valve plates. When conditions are met to open valves, PCM energizes IMSC solenoid and vacuum is then applied to actuator to pull butterfly plates open.

Linkage from actuator attaches to manifold butterfly plate lever. IMSC actuator and manifold are a composite/plastic with a single intake air passage for each cylinder. The passage has a butterfly valve plate that blocks 60 percent of intake opening when actuated, leaving top of intake passage open to generate turbulence. A return spring is used to hold butterfly valve plates closed. Vacuum actuator provides feedback to PCM indicating butterfly valve plate position.

When engine speed is less than 3000 RPM, vacuum solenoid will be energized to allow manifold vacuum to be applied and butterfly valve plates will remain closed. When engine speed is 3000 RPM or more, vacuum solenoid is de-energized to allow vacuum to vent from actuator and butterfly valve plates will open.

Scheme 11

Scheme 12

Intake Manifold Tuning Valve - 3.0L (VIN S), Econoline & Pickup 4.6L (VIN W), & 5.4L 4V (VIN A)

Intake Manifold Tuning Valve (IMTV) is an electric actuator mounted directly to intake manifold. IMTV operates a shutter device attached to electric actuator shaft. When electric actuator is energized, it rotates shaft and opens shutter, allowing both sides of the manifold airflow to blend together. (Scheme 13)- (Scheme 16).

There is no monitor feedback to PCM from IMTV to indicate shutter position (open or closed). PCM uses a positive change in throttle position sensor along with the increase in engine RPM from crankshaft position sensor to open shutter.

When engine speed is below 2600 RPM, electric actuator will not be energized, allowing IMTV shutter to remain in closed position (no airflow blend occurs). When engine speed is 2600 RPM or more, electric actuator is initially energized at a 100 percent duty cycle, causing shutter to open position (airflow blend occurs). Duty cycle then falls to about 50 percent duty cycle to continue to hold shutter open.

Scheme 13

Scheme 14

Scheme 15

Scheme 16

POWERTRAIN CONTROL MODULE

Powertrain Control Module (PCM) monitors engine operating conditions by input received from engine sensors. PCM receives input from sensors and other electronic components, such as switches or relays. Based on information received and programmed into its memory, PCM generates output signals to control various components, such as relays, solenoids and actuators.

Note. Components are grouped into 2 categories. The first category covers INPUT DEVICES , which control or produce voltage signals monitored by PCM. The second category covers OUTPUT SIGNALS , covering components controlled by PCM.

There are 2 types of PCM used. A 150-pin PCM which has 3 separate electrical harness connectors (Explorer, LS, Mountaineer and Thunderbird), and a 104-pin PCM which has one electrical harness connector (all others). (Scheme 17)and (Scheme 18). For PCM location, see POWERTRAIN CONTROL MODULE LOCATION table.

PCM uses a memory integrated circuit chip which stores information for Keep Alive Random Access Memory (KAM). For additional KAM information, see KEEP ALIVE RANDOM ACCESS MEMORY under POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS. Flash Electrically Erasable Programmable Read Only Memory (EEPROM) is an Integrated Circuit (IC) within PCM. This IC contains software code required by PCM to control powertrain. For additional EEPROM information, see FLASH ELECTRICALLY ERASABLE PROGRAMMABLE READ ONLY MEMORY under POWERTRAIN CONTROL SOFTWARE.

In the event that one or more input sensors fail, PCM initiates an alternative operating procedure called Failure Mode Effects Management (FMEM) to allow the vehicle to maintain driveability. For additional information on FMEM, see FAILURE MODE EFFECTS MANAGEMENT under POWERTRAIN CONTROL SOFTWARE. If PCM detects an engine overheating condition, it activates a fail-safe cooling strategy. For additional information, see FAIL-SAFE COOLING STRATEGY under POWERTRAIN CONTROL SOFTWARE. In the event of PCM failure, Hardware Limited Operation Strategy (HLOS) will be activated. For additional information on HLOS, see HARDWARE LIMITED OPERATION STRATEGY under POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS.

POWERTRAIN CONTROL MODULE LOCATION

Scheme 17

Scheme 18

Hardware Limited Operation Strategy

HLOS is a system of alternate circuitry that provides minimal engine operation if the PCM or EEPROM fails. During HLOS, all self-test function will stop and system will be controlled by electronic hardware.

HLOS Allowable Output Functions

1. Spark Output Controlled Directly By CKP Signal
2. Fixed Fuel Pulse Width Synchronized With CKP Signal
3. Fuel Pump Relay Energized
4. Idle Speed Control Output Signal Functional

HLOS Disabled Outputs To Default State

1. EGR Solenoids
2. No Torque Converter Clutch Lock-Up

Integrated Electronic Ignition System

Integrated Electronic Ignition (EI) System consists of a Crankshaft Position (CKP) sensor, coil pack(s), connecting wiring, and PCM. Coil On Plug (COP) Integrated EI System uses a separate coil for each spark plug and each coil is mounted directly onto plug. COP Integrated EI System eliminates the need for spark plug wires but does require input from Camshaft Position (CMP) sensor. For additional EI system information, see INTEGRATED ELECTRONIC IGNITION SYSTEM under IGNITION SYSTEMS.

Keep Alive Random Access Memory

Keep Alive Random Access Memory (KAM) stores memory of vehicle operating conditions and then uses this information for adaptive learning. KAM remains powered with ignition off so that input and output information is not lost.

Vehicle Buffered Power

Vehicle Buffered Power (VBPWR) is a PCM supplied power source that supplies regulated voltage (10-14 volts) to Visctronic Drive Fan (VDF) Fan Speed Sensor (FANSS) under normal operating conditions. It regulates to VPWR minus 1.5 volts, and voltage output is limited to protect sensor. For additional VDF clutch information, see VISCTRONIC DRIVE FAN CLUTCH under OUTPUT SIGNALS.

Vehicle Power

When ignition switch is turned to START or RUN position, battery positive voltage (B+) is applied to coil of PCM power relay. Since other end of coil is wired to ground, this energizes coil and closes contacts of PCM power relay. Vehicle power (VPWR) is now sent to PCM and various OBD-II systems.

Vehicle Reference Voltage

Vehicle Reference Voltage (VREF) is a positive voltage (about 5 volts) that is output by PCM. This is a consistent voltage that is used by 3-wire sensors.

Mass Air Flow Return

Mass Air Flow Return (MAF RTN) is a dedicated analog signal return from Mass Air Flow (MAF) sensor. It serves as a ground offset for analog voltage differential input by MAF sensor to PCM.

Signal Return

Signal Return (SIG RTN) is a dedicated ground circuit used by most OBD-II sensors and some other inputs.

Power Ground

Power Ground (PWR GND) is an electric current path return for VPWR voltage circuit. The purpose of PWR GND is to maintain sufficient voltage at PCM.

Gold Plated Terminals

Note. Damaged gold terminals should only be replaced with NEW gold terminals.

Some engine control hardware has gold plated terminals on connectors and mating harness connectors to improve electrical stability for low current draw circuits and to enhance corrosion resistance. OBD-II components equipped with gold terminals will vary by vehicle application.

Engine RPM/Vehicle Speed Limiter

PCM will disable some or all fuel injectors whenever an engine RPM or vehicle overspeed condition is detected. This prevents damage to the powertrain. Excessive wheel slippage caused by sand, gravel, rain, mud, snow, ice, etc. or excessive and sudden increase in RPM while in NEUTRAL or while driving may cause engine RPM/vehicle speed limiter to be enabled. When engine RPM/vehicle speed limiter has been enabled, vehicle will exhibit a rough running engine condition, and PCM will store DTC P1270. After driver reduces excessive speed, engine will return to normal operating mode. No repairs are required. Technician should clear DTC from PCM and inform customer of the reason for DTC. Excessive wheel slippage may be caused by sand, gravel, rain, mud, snow, ice, etc. or excessive and sudden increase in RPM while in Neutral or while driving.

Fail-Safe Cooling Strategy

Fail-safe cooling strategy is activated by PCM only in the event that an overheating condition has been detected. This strategy provides engine temperature control when cylinder head temperature exceeds certain limits. Cylinder head temperature is measured by Cylinder Head Temperature (CHT) sensor. For additional CHT sensor information, see CYLINDER HEAD TEMPERATURE SENSOR under INPUT DEVICES.

Note. Not all vehicles equipped with a CHT sensor will have fail-safe cooling strategy.

A cooling system failure such as low coolant or coolant loss could cause an overheating condition. As a result, damage to major engine components could occur. Along with a CHT sensor, fail-safe cooling strategy is used to prevent damage by allowing air cooling of engine. This strategy allows the vehicle to be driven safely for a short time with some loss of performance when an overheating condition exists. Engine temperature is controlled by varying and alternating the number of disabled fuel injectors. This allows all cylinders to cool. When fuel injectors are disabled, their respective cylinders work as air pumps, and this air is used to cool the cylinders. The more fuel injectors that are disabled, the cooler the engine runs, but the engine has less power.

Note. A Wide Open Throttle (WOT) delay is incorporated if CHT temperature is exceeded during WOT operation. At WOT, injectors will function for a limited amount of time allowing customer to complete a passing maneuver.

Before injectors are disabled, fail-safe cooling strategy alerts customer to a cooling system problem by moving instrument cluster temperature gauge to HOT zone and a PCM DTC P1285 is set. Depending on the vehicle, other indicators, such as an audible chime or warning lamp, can be used to alert customer of fail-safe cooling. If overheating continues, fail-safe cooling strategy begins to disable fuel injectors, a DTC P1299 is stored in PCM memory and a Malfunction Indicator Light (MIL), either CHECK ENGINE or SERVICE ENGINE SOON will illuminate. If overheating condition continues and a critical temperature is reached, all fuel injectors are turned off and engine is disabled.

Failure Mode Effects Management

Failure Mode Effects Management (FMEM) is an alternate system strategy in PCM designed to maintain engine operation if one or more sensor inputs fail. When a sensor input is perceived to be out-of-limits by PCM, an alternative strategy is initiated. PCM substitutes a fixed value and continues to monitor incorrect sensor input. If suspect sensor operates within limits, PCM returns to normal engine operational strategy. All FMEM sensors display a sequence error message on scan tool. Message may or may not be followed by Key On Engine Off (KOEO) or Continuous Memory DTCs when attempting Key On Engine Running (KOER) self-test mode.

Flash Electrically Erasable Programmable Read Only Memory

Flash Electrically Erasable Programmable Read Only Memory (EEPROM) is an Integrated Circuit (IC) within PCM. This IC contains software code required by PCM to control powertrain. EEPROM can be electrically erased and then reprogrammed without removing PCM from vehicle. If a software change is required to PCM, PCM can be reprogrammed through Data Link Connector (DLC) using scan tool.

Fuel Trim

Fuel control system uses a fuel trim table to compensate for normal variability of fuel system components caused by wear or aging. During closed loop vehicle operation, if fuel system appears "biased" (lean or rich), the fuel trim table will shift fuel delivery calculations to remove bias. Fuel system monitor has 2 means of adapting Short Term Fuel Trim (FT) and Long Term Fuel Trim (FT). Short Term FT is referred to as LAMBSE and Long Term FT references the fuel trim table in Keep Alive Random Access Memory (RAM).

Short Term FT is displayed as SHRTFT1 and SHRTFT2 on scan tool and is a parameter that indicates short-term fuel adjustments. Short Term FT is commonly referred to as LAMBSE. LAMBSE is calculated by PCM from Heated Oxygen Sensor (HO2S) inputs and helps maintain a 14.7:1 air/fuel ratio during closed loop operation. This range is displayed in percentage (%). A negative percentage means HO2S is indicating RICH and PCM is attempting to lean the mixture. Ideally, Short Term FT may remain near zero percent but can adjust between -25 to +35 percent.

Long Term FT is displayed as LONGFT1 and LONGFT2 on scan tool and is the other parameter that indicates long-term fuel adjustments. Long Term FT is also referred to as Fuel Trim. Long Term FT is calculated by PCM using information from Short Term FT to maintain a 14.7:1 air/fuel ratio during closed loop operation. Fuel Trim strategy is expressed in percentages. The range of authority for Long Term FT is from -35 to +35 percent. Ideal value is near zero percent, but variations of plus or minus 20 percent are acceptable. Information gathered at different speed load points are stored in fuel trim cells in fuel trim tables, which can be used in fuel calculation.

Short Term FT and Long Term FT work together. If HO2S indicates engine is running rich, PCM will correct rich condition by moving Short Term FT in the negative range (less fuel to correct for a rich combustion). If after a certain amount of time Short Term FT is still compensating for a rich condition, PCM "learns" this and moves Long Term FT into negative range to compensate and allows Short Term FT to return to a value near zero percent.

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 - EEC-V - GASOLINE & NGV 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 - EEC-V - GASOLINE & NGV 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

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 a vehicle dictates a more efficient method of communication. Multiplexing is a process of communicating several messages over the same signal path. This process allows multiple modules to communicate with each other and to the PCM using Standard Corporate Protocol (SCP) BUS(+) and BUS(-) circuits, which determine the priority in which the signals are sent. For additional information, see STANDARD CORPORATE PROTOCOL . Multiplexing reduces the weight of the vehicle by reducing electrical wiring.

Standard Corporate Protocol

Standard Corporate Protocol (SCP) is a communication language, used to exchange bi-directional messages (signals) between stand-alone modules and devices. This allows 2 or more signals to be sent over one circuit. Included in these messages is diagnostic data that is output over BUS(+) and BUS(-) lines to the Data Link Connector (DLC). This information is accessible with a scan tool.

DIAGNOSTIC MONITORS

Starting with 2002 model year, all California passenger cars and trucks (up to 14,000 GVW) and all federal passenger cars and trucks (up to 8500 GVW) are required to comply with either CARB-OBD-II or EPA OBD requirements. Federal heavy-duty truck up to 10,000 lb. GVWR choosing to certify using Light Duty Truck provisions must comply with OBD-II requirements. Federal heavy-duty trucks over 8500 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 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.

Catalyst Efficiency Monitor Description

Catalyst Efficiency Monitor uses an oxygen sensor before and after catalyst to infer hydrocarbon efficiency based on oxygen storage capacity of catalyst. Under normal, closed-loop fuel conditions, high efficiency catalysts have significant oxygen storage. This makes switching frequency of rear Heated Oxygen Sensor (HO2S) very slow and reduces amplitude of those switches as compared to switching frequency and amplitude of front HO2S. As catalyst efficiency deteriorates due to thermal and/or chemical deterioration, its ability to store oxygen declines. Post-catalyst or downstream HO2S signal begins to switch more rapidly with increasing amplitude, approaching switching frequency and amplitude of pre-catalyst or upstream HO2S.

Note. The predominant failure mode for high mileage catalysts is chemical deterioration (phosphorus deposition on front brick of catalyst), not thermal deterioration.

All vehicles utilize a Federal Test Procedure (FTP) based catalyst monitor. Meaning catalyst monitor must run during a standard FTP emission test. This differs from a 20 second steady state catalyst monitor used in 1994-96 vehicles. Currently, 2 slightly different versions of catalyst monitor are utilized; Switch Ratio Method and Index Ratio Method. Beginning with 2001 model year, both versions will continue to be used. See CATALYST EFFICIENCY MONITOR - SWITCH RATIO METHOD (1996-2002) or CATALYST EFFICIENCY MONITOR - INDEX RATIO METHOD (SOME 2001-LATER) .

Catalyst Efficiency Monitor - Switch Ratio Method (1996-2002)

In order to assess catalyst oxygen storage, monitor counts front and rear HO2S switches during part-throttle, closed-loop fuel condition after engine is warmed-up and inferred catalyst temperature is within limits. Front switches are accumulated in up to 9 different air mass regions or cells although 3 air mass regions is typical. Rear switches are counted in a single cell for all air mass regions. When required number of front switches has accumulated in each cell, the total number of rear switches is divided by total number of front switches to compute a switch ratio. A switch ratio near zero indicates high oxygen storage capacity. Therefore, high HC efficiency. A switch ratio near one, indicates low oxygen storage capacity. Therefore, low HC efficiency. If actual switch ratio exceeds a calibrated threshold switch ratio, the catalyst is considered faulty. Inputs from ECT or CHT (warm engine), IAT (not extreme ambient temperatures), MAF (greater than minimum engine load), VSS (within vehicle speed window) and TP (at part-throttle) are required to enable Catalyst Efficiency Monitor.

The following are typical switch ratio monitor entry conditions

1. Part throttle with no rapid throttle transients.
2. Minimum 330 seconds since start-up at 70°F (21°C).
3. ECT or CHT is 170-230°F (76.6-110°C).
4. IAT is 20-180°F (-6°C to 82°C)
5. Engine load more than 10 percent.
6. Time since entering close loop is 30 seconds.
7. Vehicle speed is 5-70 MPH.
8. Mass air flow is 1-5 lbs/minute.
9. Fuel level more than 15 percent.
10. EGR is 1-12 percent.

DTCs associated with this test are DTC P0420 (Bank No. 1 or "Y" pipe system), and P0430 (Bank No. 2). Because an exponentially weighted moving average algorithm is used for malfunction determination, up to 6 driving cycles may be required to illuminate MIL during normal customer driving. If KAM is reset or battery is disconnected, a malfunction will illuminate MIL in 2 drive cycles.

Catalyst Efficiency Monitor - Index Ratio Method (Some 2001-Later)

In order to assess catalyst oxygen storage, catalyst monitor counts front HO2S switches during part-throttle, closed-loop fuel conditions after engine is warmed-up and inferred catalyst temperature is within limits. Front switches are accumulated in up to 3 different air mass regions or cells. While catalyst monitoring entry conditions are being met, front and rear HO2S signal lengths are continually being calculated. When required number of front switches has accumulated in each cell, total signal length of rear HO2S is divided by total signal length of front HO2S to compute a catalyst index ratio. An index ratio near zero, indicates high oxygen storage capacity. Therefore, high efficiency. A switch ratio near one, indicates low oxygen storage capacity. Therefore, low HC efficiency. If actual index ratio exceeds threshold index ratio, catalyst is considered faulty. Inputs from ECT or CHT (warm engine), IAT (not extreme ambient temperatures), MAF (greater than minimum engine load), VSS (within vehicle speed window) and TP (at part-throttle) are required to enable Catalyst Efficiency Monitor.

The following are typical switch ratio monitor entry conditions

1. Part throttle, maximum rate of change 0.2 volt/0.050 second.
2. Minimum 330 seconds since start-up at 70°F (21°C).
3. ECT or CHT is 170-230°F (76.6-110°C).
4. IAT is 20-180°F (-6 to 82°C).
5. Engine load 15-40 percent (depending on air mass cell).
6. Time since entering close loop is 30 seconds.
7. Vehicle speed is 5-70 MPH.
8. Fuel level more than 15 percent.
9. EGR is 1-12 percent.

DTCs associated with this test are DTC P0420 (Bank No. 1 or Y-pipe system), and P0430 (Bank No. 2). Because an exponentially weighted moving average algorithm is used for malfunction determination, up to 6 driving cycles may be required to illuminate MIL during normal customer driving. If KAM is reset or battery is disconnected, a malfunction will illuminate MIL in 2 drive cycles.

General Catalyst Monitor Operation

Monitor execution is once per drive cycle. In order for catalyst monitor to run, HO2S monitor must be complete and Secondary AIR and EVAP system functional with no stored DTCs. If catalyst monitor does not complete during a particular driving cycle, the already accumulated switch/signal data is retained in Keep Alive Memory (KAM) and is used during next driving cycle to allow catalyst monitor a better opportunity to complete. Rear HOS2 sensors can be located in various configurations to monitor different kinds of exhaust systems. In-line engines and many V-engines are monitored by their individual bank. A rear HO2S sensor is used along with the front fuel control HO2S sensor for each bank. These 2 sensors are used on an in-line engine; 4 sensors are used on a V-engine. Some V-engines have exhaust banks that combine into a single underbody catalyst. These systems are referred to as Y-pipe systems. They use only one rear HO2S sensor along with 2 front, fuel-control HO2S sensors. Y-pipe system uses 3 sensors in all. For "Y" piped systems, 2 front HO2S sensor signals are combined by PCM software to infer what HO2S signal would have been in front of monitored catalyst. Inferred front HO2S signal and the actual single rear HO2S signal is then used to calculate switch ratio.

Most vehicles that are part of Low Emission Vehicle (LEV) catalyst monitor phase-in will monitor less than 100 percent of catalyst volume. Often this is the first catalyst brick of catalyst system. Partial volume monitoring is done on LEV and Ultra Low Emission Vehicle (ULEV) vehicles in order to meet the 1.75 grams per mile emission standard for smog causing carbon monoxide (CO). Many applications that utilize partial-volume monitoring place rear HO2S sensor after first light-off catalyst can or, after second catalyst can in a 3-can per bank system. A few applications place HO2S in middle of catalyst can, between first and second bricks. Index ratios for Ethanol (Flex-fuel) vehicle vary based on the changing concentration of alcohol in fuel. The malfunction threshold typically increases as percentage of alcohol increases. For example, a malfunction threshold of 0.5 may be used at E10 (10 percent ethanol) and 0.9 may be used at E85 (85 percent ethanol). Malfunction thresholds are therefore adjusted based on percentage of alcohol in fuel.

Comprehensive Component Monitor

Comprehensive Component Monitor (CCM) monitors for malfunctions in any powertrain electronic component or circuit that provides input or output signals to PCM that can affect emissions and is not monitored by another OBD-II monitor. Inputs and outputs are, at a minimum, monitored for circuit continuity or proper range of values. Where feasible, inputs are also checked for rationality, outputs are also checked for proper functionality. CCM covers many components and circuits and tests them in various ways depending on hardware, function, and type of signal. For example, analog inputs such as Throttle Position (TP) or Engine Coolant Temperature (ECT) are typically checked for opens, shorts and out-of-range values. This type of monitoring is performed continuously. Some digital inputs like Vehicle Speed (VS) or Crankshaft Position (CKP) rely on rationality checks; checking to see if input value makes sense at current engine operating conditions. These types of tests may require monitoring several components and can only be performed under appropriate test conditions. Outputs such as Idle Air Control (IAC) solenoid are checked for opens and shorts by monitoring a feedback circuit or "smart driver" associated with the output. Other outputs, such as relays, require additional feedback circuits to monitor secondary side of relay. Some outputs are also monitored for proper function by observing reaction of control system to a given change in output command. An IAC solenoid can be functionally tested by monitoring idle RPM relative to target idle RPM. Some tests can only be performed under appropriate test conditions; for example, transmission shift solenoids can only be tested when PCM commands a shift.

The following is an example of some input and output components monitored by CCM. Components monitored may belong to engine, ignition, transmission, air conditioning, or any other PCM supported subsystem.

1. Inputs Mass Air Flow (MAF) sensor, Intake Air Temperature (IAT) sensor, Engine Coolant Temperature (ECT) sensor, Throttle Position (TP) sensor, Camshaft Position (CMP) sensor, Air Conditioning Pressure Sensor (ACPS) and Fuel Tank Pressure (FTP) sensor.
2. Outputs Fuel Pump (FP), Wide Open Throttle A/C Cutout (WAC), Idle Air Control (IAC), Shift Solenoid (SS), Torque Converter Clutch (TCC) solenoid, Intake Manifold Runner Control (IMRC), EVAP Canister Purge Valve, Canister Vent (CV) solenoid.

CCM is enabled after engine starts and is running. A DTC is stored in Keep Alive Memory (KAM) and MIL is illuminated after 2 driving cycles when a malfunction is detected. Many CCM tests are also performed during KOEO and KOER self-tests.

Evaporative Emission Leak Check Monitor

Evaporative Emission (EVAP) Leak Check Monitor is an on-board strategy designed to detect a leak from a hole (opening) equal to or more than 0.040" (1.016 mm) in enhanced EVAP system. Proper function of individual components of enhanced EVAP system as well as its ability to flow fuel vapor to engine is also examined. EVAP leak check monitor relies on individual components of enhanced EVAP system to apply vacuum to fuel tank and then seal entire enhanced EVAP system from atmosphere. Fuel tank pressure is then monitored to determine total vacuum lost (bleed-up) for a calibrated period of time. Inputs from Engine Coolant Temperature (ECT) or Cylinder Head Temperature (CHT) sensor, Intake Air Temperature (IAT) sensor, Mass Air Flow (MAF) sensor, vehicle speed, Fuel Level Input (FLI) and Fuel Tank Pressure (FTP) sensor are required to enable EVAP Leak Check Monitor.

Note. During EVAP Leak Check Monitor Repair Verification Drive Cycle, a PCM reset will bypass the minimum soak time required to complete monitor. See OBD-II DRIVE CYCLE DESCRIPTION under DRIVE CYCLE PROCEDURE under DIAGNOSTIC MONITORS in SELF-DIAGNOSTICS - EEC-V - GASOLINE & NGV article. EVAP Leak Check Monitor will not run if key is turned off after a PCM reset. EVAP Leak Check Monitor will not run if a MAF sensor failure is indicated. EVAP Leak Check Monitor will not initiate until Heated Oxygen Sensor (HO2S) Monitor has completed.

EVAP Leak Check Monitor is executed by individual components of enhanced EVAP system as follows

1. EVAP canister purge valve function is to create a vacuum in fuel tank. A minimum duty cycle on EVAP canister purge valve (75 percent) must be met before EVAP Leak Check Monitor can begin.
2. Canister Vent (CV) solenoid will close (100 percent duty cycle) with EVAP canister purge valve at its minimum duty cycle to seal enhanced EVAP system from atmosphere and obtain a target vacuum on fuel tank.
3. Fuel Tank Pressure (FTP) sensor will be used by EVAP Leak Check Monitor to determine if target vacuum on fuel tank is being reached to perform leak check. Some vehicle applications with EVAP Leak Check Monitor use a remote in-line FTP sensor. Once target vacuum on fuel tank is achieved, change in fuel tank vacuum for a calibrated period of time will determine if a leak exists. If initial target vacuum cannot be reached, DTC P0455 (gross leak detected) will be set. EVAP Leak Check Monitor will abort and not continue with leak check portion of test. For some vehicle applications; if initial target vacuum cannot be reached after a refueling event and purge vapor flow is excessive, DTC P0457 (fuel cap off) is set. If initial target vacuum cannot be reached and purge flow is too small, DTC P1443 (no purge flow condition) is set. If initial target vacuum is exceeded, a system flow fault exists and DTC P1450 (unable to bleed-up fuel tank vacuum) is set. EVAP Leak Check Monitor will abort and not continue with leak check portion of test. If target vacuum is obtained on fuel tank, change in fuel tank vacuum (bleed-up) will be calculated for a calibrated period of time. Calculated change in fuel tank vacuum will be compared to a calibrated threshold for a leak from a hole (opening) of 0.040" (1.016 mm) in enhanced EVAP system. If calculated bleed-up is less than calibrated threshold, enhanced EVAP system passes. If calibrated bleed-up exceeds calibrated threshold, test will abort and rerun test up to 3 times. If bleed-up threshold is still being exceeded after 3 tests, a vapor generation check must be performed before DTC P0442 (small leak detected) will be set. This is accomplished by returning enhanced EVAP system to atmospheric pressure by closing EVAP canister purge valve and opening CV solenoid. Once FTP sensor observes fuel tank is at atmospheric pressure, CV solenoid closes and seals enhanced EVAP system. The fuel tank pressure build-up for a calibrated period of time will be compared to a calibrated threshold for pressure build-up due to vapor generation. If fuel tank pressure build-up exceeds threshold, leak test results are invalid due to vapor generation. EVAP Leak Check Monitor will attempt to retest again. If fuel tank pressure build-up does not exceed threshold, leak test results are valid and DTC P0442 will be set. NOTE: If the vapor generation is high on some vehicle Enhanced EVAP Systems, where the monitor does not pass, the result is treated as a no test. Thereby, the test is complete for the day. If the 0.40" (1.016 mm) test passes, test time is extended to allow 0.020" (0.508 mm) test to run. Calculated change in fuel vacuum over extended time is compared to a calibrated threshold for a leak from a 0.020" (0.508 mm) hole (opening). If calculated bleed-up exceeds calibrated threshold, vapor generation is run. If vapor generation passes (no vapor generation), an internal flag is set in PCM to run a 0.020" (0.508 mm) test at idle (vehicle stopped). On the next start following a long engine off period, enhanced EVAP system will be sealed and evacuated for first 10 minutes of operation. If appropriate conditions are met, a 0.020" (0.508 mm) leak check is conducted at idle. If test at idles fails, a DTC P0456 will be set. There is no vapor generation test with idle test.
4. Malfunction Indicator Lamp (MIL) is activated for DTCs P0442, P0455, P0456, P0457, P1443 and P1450 (or P446) after two occurrences of the same fault. The MIL can also be activated for any Enhanced EVAP system component DTCs in the same manner. The Enhanced EVAP system component DTCs P0443, P0452, P0453 and P1451 are tested as part of Comprehensive Component Monitor (CCM). For additional information, see «COMPREHENSIVE COMPONENT MONITOR»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv__comprehensive-component-monitor) .

Exhaust Gas Recirculation System Monitor - Differential Pressure Feedback EGR

Differential Pressure Feedback EGR (DPFE) system monitor is an on-board strategy designed to test integrity and flow characteristics of EGR system. The monitor is activated during EGR system operation and after certain base engine conditions are satisfied. Input from ECT, CHT, IAT, TP and CKP sensors is required to activate EGR system monitor. Once activated, EGR system monitor will perform each test listed during engine modes and conditions indicated. Some EGR system monitor tests are also performed during KOEO or KOER self-test

1. DPFE sensor and circuit are continuously tested for opens and shorts. The monitor looks for DPFE circuit voltage to exceed maximum or minimum allowable limits. DTCs associated with this test are DTCs P1400 and P1401.
2. EGR vacuum regulator solenoid is continuously tested for opens and shorts. The monitor looks for an EGR Vacuum Regulator (EGRVR) circuit voltage that is inconsistent with EGRVR circuit commanded output state. DTC associated with this test is DTC P1409.
3. Test for a stuck open EGR valve or EGR flow at idle is continuously performed whenever at idle (TP sensor indicating closed throttle). The monitor compares DPFE circuit voltage at idle to DPFE circuit voltage stored during KOEO self-test to determine if EGR flow is present at idle. DTC associated with this test is DTC P0402.
4. DPFE sensor upstream hose is tested once per drive cycle for disconnect and plugging. The test is performed with EGR valve closed and during a period of acceleration. PCM will momentarily command EGR valve closed. The monitor looks for DPFE sensor voltage to be inconsistent for a no flow voltage. A voltage increase or decrease during acceleration while EGR valve is closed may indicate a fault with signal hose during this test. DTC associated with this test is DTC P1405.
5. EGR flow rate test is performed during a steady state when engine speed and load are moderate and EGR vacuum regulator duty cycle is high. The monitor compares DPFE circuit voltage to a desired EGR flow voltage for that state to determine if EGR flow rate is acceptable or insufficient. This is a system test and may trigger a DTC for any fault causing EGR system to fail. DTC associated with this test is DTC P0401. DTC P1408 is similar to P0401, but performed during KOER self-test conditions.
6. The MIL is activated after one of the above tests fails on 2 consecutive drive cycles.

Electric Exhaust Gas Recirculation System Monitor

Electric Exhaust Gas Recirculation (EEGR) system monitor is an on-board strategy designed to test integrity and flow characteristics of EEGR system. The monitor is activated during EEGR system operation and after certain base engine conditions are satisfied. Input from ECT or CHT, IAT, TP, CPS, MAF, and MAP sensors is required to activate EEGR System Monitor. Once activated, EEGR system monitor will perform each test listed during engine modes and conditions indicated. Some EEGR system monitor tests are also performed during KOEO and KOER self-tests.

1. The motor EGR monitor consists of an electrical and functional test that checks motor and EEGR system for proper flow. PCM controls EEGR valve by commanding from 0-52 discreet increments or "steps" to get valve from fully CLOSED to fully OPEN position. Motor electrical test is a continuous check of 4 electric motor coils and circuits to PCM. A malfunction is indicated if an open circuit, short to power, or short to ground has occurred in one or more motor coils/circuits for a calibrated period of time. If a malfunction has been detected, EEGR system will be disabled, setting KOER, and Continuous Memory DTC P0403. Additional monitoring will be suspended for remainder of driving cycle, or until next engine start-up. After the vehicle has warmed up and normal EEGR rates are being commanded by PCM, EEGR flow check is performed. Flow test is performed once per drive-cycle when a minimum amount of EEGR is requested and remaining entry conditions required to initiate test are satisfied. If a malfunction is detected, EEGR system as well as EEGR monitor is disabled until next engine start-up.
2. EEGR flow test is done by observing the behavior of 2 different values of MAP; analog MAP sensor reading, and inferred MAP reading (a MAP reading calculated from MAF sensor, TP sensor, RPM, etc.). During normal, steady-state operating conditions, EEGR is intrusively commanded ON to a specified percentage. Then, EEGR is commanded OFF. If EEGR system is working properly, there is a significant difference in both observed and calculated values of MAP, between EEGR ON and EEGR OFF states. When flow test entry conditions have been satisfied, EEGR is commanded to flow at a calibrated test rate (about 10 percent). At this time, value of MAP is recorded (EEGR ON MAP). Value of inferred MAP EEGR ON IMAP is also recorded. Next, EEGR is commanded OFF (zero percent). Again, value of MAP is recorded (EEGR OFF MAP). Value of EEGR OFF IMAP is also recorded. Typically, 7 such ON/OFF samples are taken. After all samples have been taken, the average EEGR ON MAP, EEGR ON IMAP, EEGR OFF MAP and EEGR OFF IMAP values are stored.
3. The differences between EEGR ON and EEGR OFF values are calculated. MAP-Delta = EEGR ON MAP - EEGR OFF MAP (Analog MAP) IMAP-Delta = EEGR ON IMAP - EEGR OFF IMAP (Inferred MAP) If the sum of MAP-Delta and IMAP-Delta exceeds a maximum threshold or falls below a minimum threshold, DTC P0400 (high or low flow malfunction) is stored.
4. As an additional check, if EEGR ON MAP exceeds a maximum threshold (BARO - a calibrated value), a DTC P0400 (low flow malfunction) is registered. This check is performed to detect reduced EEGR flow on systems where MAP pickup point is not located in intake manifold, but is located just upstream of EEGR valve in EEGR delivery tube. NOTE: BARO is inferred at engine start-up using KOEO MAP sensor reading. It is updated during high, part-throttle or high RPM engine operation.
5. If inferred ambient temperature is less than 20°F (-7°C), more than 130°F (54°C), or altitude is more than 8000 feet (BARO less than 22.5 In. Hg), EEGR flow test cannot be reliably done. In these conditions, EEGR flow test is suspended and a timer starts to accumulate the time in these conditions. If vehicle leaves these extreme conditions, timer starts and if conditions permit, will attempt to complete EEGR flow monitor. If timer reaches 500 seconds, EEGR flow test is disabled for remainder of current driving cycle and EEGR monitor I/M readiness bit will be set to a "ready" condition.

DTC P1408 is like DTC P0400. It will indicate an EEGR flow failure (outside minimum or maximum limits) but is only set during KOER self test. DTC P0400 and P0403 will illuminate MIL. DTC P1408 will not illuminate MIL.

Fuel System Monitor

Fuel System Monitor is an on-board strategy designed to monitor the fuel trim system. The fuel control system uses fuel trim tables stored in PCM Keep Alive Memory (KAM) to compensate for variability in fuel system components due to normal wear and aging. During closed-loop vehicle operation, fuel trim strategy learns corrections needed to correct a "biased" rich or lean fuel system. Correction is stored in fuel trim tables. Fuel trim has 2 means of adapting; a Long Term Fuel Trim (LONGFT) and a Short Term Fuel Trim (SHRTFT). Long term relies on fuel trim tables and short term refers to desired air/fuel ratio parameter "LAMBSE". For additional fuel trim information, see FUEL TRIM under POWERTRAIN CONTROL SOFTWARE in THEORY & OPERATION - EEC-V - GASOLINE & NGV. Input from ECT or CHT, IAT, and MAF sensors is required to activate fuel trim system, which in turn activates fuel system monitor. Once activated, fuel system monitor looks for fuel trim tables to reach adaptive clip and LAMBSE to exceed a calibrated limit. Fuel system monitor will store appropriate DTC when a fault is detected as follows.

1. Heated Oxygen Sensor (HO2S) detects presence of oxygen in exhaust and provides PCM with feedback indicating air/fuel ratio.
2. A correction factor is added to fuel injector pulse width calculation according to long and short term fuel trims as needed to compensate for variations in fuel system.
3. When deviation in the parameter LAMBSE increases, air/fuel control suffers and emissions increase. When LAMBSE exceeds a calibrated limit and the fuel trim table has clipped, the Fuel System Monitor sets a Diagnostic Trouble Code (DTC) as follows: DTCs P0171 and P0174 are associated with monitor detecting a lean shift in fuel system operation. DTCs P0172 and P0175 are associated with the monitor detecting a rich shift in fuel system operation.
4. MIL is activated after a fault is detected on 2 consecutive drive cycles.

Heated Oxygen Sensor Monitor

Heated Oxygen Sensor (HO2S) monitor is an on-board strategy designed to monitor HO2S sensors for a malfunction or deterioration which can affect emissions. The fuel control or upstream HO2S is checked for proper output voltage and response rate (time it takes to switch from lean to rich or rich to lean). Downstream HO2S sensors used for catalyst monitor are also monitored for proper output voltage. Input is required from ECT or CHT, IAT, MAF and CKP sensors to activate HO2S monitor. Fuel system monitor and misfire detection monitor must also have completed successfully before HO2S monitor is enabled.

1. HO2S sensor senses oxygen content in exhaust flow and outputs a voltage between zero and one volt. Lean of stoichiometric (air/fuel ratio of approximately 14.7:1); HO2S will generate a voltage between zero and 0.45 volt. Rich of stoichiometric; HO2S will generate a voltage between 0.45 and one volt. HO2S monitor evaluates both upstream HO2S (fuel control), and downstream HO2S (catalyst monitor) for proper function.
2. Once HO2S monitor is enabled, upstream HO2S signal voltage amplitude and response frequency are checked. Excessive voltage is determined by comparing HO2S signal voltage to a maximum calibratable threshold voltage. A fixed frequency closed-loop fuel control routine is executed and upstream HO2S voltage amplitude and output response frequency are observed. A sample of upstream HO2S signal is evaluated to determine if sensor is capable of switching or has a slow response rate. An HO2S heater circuit fault is determined by turning heater on and off and looking for a corresponding change in Output State Monitor (OSM) and by measuring current going through heater circuit. HO2S monitor DTCs can be categorized as follows: DTCs P1130, P1131, P1132, P1150, P1151 and P1152 are associated with HO2S lack of switching. DTCs P0133 and P0153 are associated with HO2S slow response rate. DTCs P0131, P0136, P0148, P0151 and P0156 are associated with HO2S signal circuit malfunction. DTCs P0135, P0141, P0155 and P0161 are associated with HO2S heater circuit malfunction. DTC P1127 is associated with downstream HO2S not running in KOER self-test. DTCs P1128 and P1129 are associated with swapped HO2S connectors.
3. MIL is activated after a fault is detected on 2 consecutive drive cycles.

Misfire Detection Monitoring

Misfire Detection Monitor is an on-board strategy designed to monitor engine misfire and identify a specific cylinder in which misfire has occurred. Misfire is defined as lack of combustion in a cylinder due to absence of spark, poor fuel metering, poor compression, or any other cause. Misfire Detection Monitor will be enabled only when certain base engine conditions are first satisfied. Input from ECT or CHT, MAF and CKP sensors is required to enable the monitor. Misfire Detection Monitor is also performed during KOEO and KOER self-test. The following occurs During Misfire Detection Monitor

1. PCM synchronized ignition spark is based on information received from CKP sensor. CKP signal generated is also main input used in determining cylinder misfire.
2. Input signal generated by CKP sensor is derived by sensing the passing of teeth from crankshaft position wheel mounted on end of crankshaft.
3. Input signal to PCM is then used to calculate time between CKP edges and also crankshaft rotational velocity and acceleration. By comparing accelerations of each cylinder event, power loss of each cylinder is determined. When power loss of a particular cylinder is smore than a calibrated value and other criteria is met, then suspect cylinder is determined to have misfired.
4. Misfire types are as follows: Misfire Type A Upon detection of a Misfire type A (200 revolutions) which would cause catalyst damage, MIL will blink once per second during actual misfire, and a DTC will be stored. Misfire Type B Upon detection of a Misfire type B (1000 revolutions) which will exceed emissions threshold or cause a vehicle to fail an inspection and maintenance tailpipe emissions test, MIL will illuminate and a DTC will be stored. The DTC associated with multiple cylinder misfire for a Type A or Type B misfire is DTC P0300. DTCs associated with an individual cylinder misfire for a Type A or Type B misfire are: DTCs P0301, P0302, P0303, P0304, P0305, P0306, P0307, P0308, P0309 and P0310.

Secondary Air Injection System Monitor - Electric Secondary Air Injection Pump System

Secondary Air Injection (AIR) system monitor is an on-board strategy designed to monitor proper function of secondary air injection system. AIR monitor for electric secondary air injection pump system consists of 2 monitor circuits: an AIR circuit to diagnose concerns with primary circuit side of Solid State Relay (SSR), and an AIR Monitor circuit to diagnose concerns with secondary circuit side of SSR. A functional check is also performed that tests ability of AIR system to inject air into exhaust. Functional check relies upon HO2S sensor feedback to determine presence of air flow. The monitor is enabled during AIR system operation and only after certain base engine conditions are first satisfied. Input is required from ECT, IAT, and CKP sensors and HO2S monitor test must also have passed without a fault detection to enable AIR monitor. AIR monitor is also activated during KOER self-test.

1. The AIR circuit is normally held high through AIR bypass solenoid and SSR when output driver is off. Therefore a low AIR circuit indicates a driver is always on and a high circuit indicates an open in PCM. DTC P0412 is associated with this test.
2. The AIR Monitor circuit is held low by resistance path through AIR pump when pump is off. If AIR monitor circuit is high, there is either an open circuit to PCM from pump, or there is power supplied to AIR Pump. If AIR monitor is low when pump is commanded ON, there is either an open circuit from SSR or SSR has failed to supply power to pump. DTCs P1413 and P1414 are associated with this test.
3. The functional check may be done in 2 parts: at start-up when AIR pump is normally commanded ON, or during a hot idle if start-up test was not able to be performed. The flow test relies upon HO2S to detect presence of additional air in exhaust when introduced by secondary air injection system. DTC P0411 is associated with this test.
4. MIL is activated after one of the above tests fail on 2 consecutive drive cycles.

Thermostat Monitor

Thermostat Monitor is designed to verify proper thermostat operation. This monitor only applies to certain applications beginning with the 2000 model year and replaces "Insufficient temperature for closed-loop test" (DTC P0125). This monitor will be executed once per drive cycle and has a monitor run duration of 300-800 seconds. If a malfunction is indicated by thermostat monitor a DTC P0125 will be set and MIL will be illuminated. The monitor checks Engine Coolant Temperature (ECT) or Cylinder Head Temperature (CHT) sensor to warm up in a predictable manner when engine is generating sufficient heat. A timer is started while engine is at moderate load and vehicle speed is above a calibrated limit. Target timer value is based on ambient air temperature at start-up. If timer exceeds the target time and ECT/CHT has not warmed up to target temperature, a malfunction is indicated. The test runs if start-up intake air temperature from IAT sensor is at, or below target temperature. A 2-hour engine off soak time is required to erase a pending or confirmed DTC. This soak time feature prevents false-passes of monitor when the engine coolant temperature rises after engine is turned off during a short engine off soak period. The target temperature will be calibrated to thermostat regulating temperature minus 20°F (11°C). For a typical 195°F (90°C) thermostat, warm-up temperature would be calibrated to 175°F (79°C).

Note. Vehicles not part of thermostat monitor phase-in, will utilize a 140°F (60°C) warm-up temperature.

1. Inputs ECT or CHT, IAT, engine LOAD (from MAF sensor) and vehicle speed input. Typical monitor entry conditions are as follows: Vehicle speed more than 15 MPH. Intake air temperature at start-up is between 20°F (-7°C) and target thermostat temperature. Engine load more than 30 percent. Engine off (soak) time to clear pending or confirmed DTC is more than 2 hours.
2. Output Malfunction Indicator Lamp (MIL)

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

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.

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 pump monitor circuit.

GENERIC ELECTRONIC MODULE

Automatic 4-Wheel Drive (A4WD) system is a full time 4-wheel drive system with an electronic shift 4x4 system that allows the operator to choose between three different 4x4 modes. The operator can switch between A4WD, and 4WD high mode at any speed, and 4WD low mode. In A4WD mode, Generic Electronic Module (GEM) varies torque split between front and rear driveline by controlling transfer case clutch. Transfer case clutch allows for slight speed differences between front and rear driveshaft which normally occurs when negotiating a corner on dry pavement. When rear wheels are overpowered, GEM detects this slip condition, and duty cycle to transfer case clutch is increased until speed difference between driveshafts is reduced.

NATURAL GAS VEHICLE MODULE

Note. F150 5.4L bi-fuel model uses an Alternative Fuel Control Module (AFCM) to allow communication between PCM and AFCM. AFCM is incorporated within compuvalve on F150 bi-fuel models. For additional information on bi-fuel system, see THEORY & OPERATION - EEC-V - BI-FUEL article.

Natural Gas Vehicle (NGV) module has 2 functions. The first function is to operate fuel injectors and is referred to as Injector Driver Module (IDM). The second function sends a fuel level indicator signal to drive the fuel gauge and is called Fuel Indicator Module (FIM). IDM vehicle fuel indicator driver signals are based on PCM fuel injector driver signals and are controlled directly by corresponding injector drivers in PCM. IDM must be used to provide NG fuel injectors with the required high current necessary for proper operation. The greater demand of fuel injector current warrants an increased size of injector driver and increased heat dissipation. Given these conditions, PCM would not be suitable for location of these drivers. IDM closely resembles 60-pin EEC-IV PCM module in appearance. See NATURAL GAS VEHICLE MODULE LOCATION table.

IDM injector drivers are capable of controlling amount of current flow to each NG fuel injector. Once fuel injector is open, IDM NG fuel injector driver will reduce current flow to a sufficient amount to continue to hold fuel injector open in an effort to reduce heat. If IDM driver does not detect required peak current to initially open NG fuel injector within a specified amount of time, IDM driver will drop current to fuel injector hold open current. The FIM is not part of the powertrain control subsystem.

NATURAL GAS VEHICLE MODULE LOCATION

INPUT DEVICES

Note. Transmission related PCM inputs are not listed here. For a complete listing of transmission related PCM inputs, see appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS.

Vehicles are equipped with different combinations of input devices. Not all devices are used on all models. To determine the input device used on a specific model, see appropriate wiring diagram in WIRING DIAGRAMS article. The available input devices include the following

A/C Cycling Switch

Note. Some applications do not have a dedicated (separate) input to PCM indicating that A/C is requested. This information is received by PCM through Standard Corporate Protocol (SCP) BUS (+) and BUS (-) circuits.

Air Conditioning (A/C) cycling switch may be wired to either the ACCS or ACPSW PCM input. When A/C cycling switch opens, PCM will turn off A/C clutch. A/C Cycling Switch (ACCS) circuit to PCM provides a voltage signal which indicates when A/C is requested. When A/C demand switch is turned on, and both A/C cycling switch and high pressure contacts of A/C high pressure switch (if equipped and in circuit) are closed, voltage is supplied to ACCS circuit at PCM. See appropriate wiring diagram in WIRING DIAGRAMS article. If ACCS signal is not received by PCM, PCM circuit will not allow A/C to operate. For additional information, see WIDE OPEN THROTTLE A/C CUT-OFF RELAY under PCM OUTPUTS.

A/C Pressure Sensor

The A/C pressure sensor is located in the high pressure (discharge) side of A/C system. A/C pressure sensor provides a voltage signal to the Powertrain Control Module (PCM) that is proportional to A/C pressure. PCM uses this information for A/C clutch control, fan control and idle speed control.

Air Conditioning Evaporator Temperature Sensor

Air Conditioning Evaporative Temperature (ACET) sensor senses evaporator air discharge temperature. ACET sensor is a thermistor device in which resistance changes with temperature. Electrical resistance of a thermistor decreases as temperature increases, and increases as temperature decreases. PCM sources a low current 5 volts on ACET circuit. With SIG RTN also connected to ACET sensor, varying resistance affects voltage drop across sensor terminals. As A/C evaporator air temperature changes, varying resistance of ACET sensor changes voltage PCM detects. ACET sensor is used to more accurately control A/C clutch cycling, improving defrost/demist performance, and reduce A/C clutch cycling.

Air Conditioning Pressure Sensor

Air Conditioning Pressure (A/C pressure) sensor is located in high pressure (discharge) side of A/C system. A/C pressure sensor provides a voltage signal to PCM that is proportional to A/C pressure. (Scheme 19) PCM uses this information for A/C clutch control, fan control and idle speed control.

Scheme 19

A/C High Pressure Switch

The A/C high pressure switch is used for additional A/C system pressure control. A/C high pressure switch is either dual function for 2-speed fan control applications or single function for all other applications. For refrigerant containment control, the normally closed high pressure contacts open at a predetermined A/C pressure. This will result in A/C turning off, preventing A/C pressure from rising to a level that would open A/C high pressure relief valve. For fan control, the normally open medium pressure contacts close at a predetermined A/C pressure. This grounds the ACPSW circuit input to Powertrain Control Module (PCM). The PCM will then turn on the high speed fan to help reduce A/C pressure.

Brake Pressure Applied/Brake Deactivator Switch

Brake Pressure Applied (BPA) switch is sometimes called Brake Deactivator switch for vehicle speed control deactivation, is a normally closed switch, which supplies battery positive voltage (B+) to PCM when brake pedal is not applied. When brake pedal is applied, the normally closed switch will open and power is removed from PCM. On some applications the normally closed BPA switch along with the normally open Brake Pedal Position (BPP) switch are used for a brake rationality test within PCM. PCM misfire monitor profile learn function can be disable if a brake switch failure occurs. If one or both brake pedal inputs to PCM did not change states when they were expected to, DTC P1572 may be set by PCM.

Brake Pedal Position Switch

Brake Pedal Position (BPP) switch is either hard wired to PCM and brakelight circuit, or broadcast over the Standard Corporate Protocol (SCP) network via another module to be received by PCM. The BPP input is used by PCM to disengage torque converter clutch and on some applications as an input for idle speed control for idle quality. If all brakelights are burned out (open circuit) on applications where BPP switch is hard wired to PCM, high voltage will be present at PCM due to a pull-up resistor in PCM, providing engine with fail-safe operation.

Camshaft Position Sensor

A 3-pin Hall Effect type Camshaft Position (CMP) sensor or a 2-pin variable reluctance sensor is used. (Scheme 20)and (Scheme 21). CMP sensor is used to determine camshaft position and to identify when piston No. 1 is on its compression stroke. CMP sensor signal is used by PCM for synchronizing the firing of sequential fuel injectors. Applications with Coil On Plug (COP) ignition also use CMP signal to select the proper ignition coil to fire. The input circuit to PCM is referred to as the CMP input or circuit.

Scheme 20

Scheme 21

Clutch Pedal Position Switch

Clutch Pedal Position (CPP) switch is mounted near clutch pedal. CPP switch is an input for Powertrain Control Module (PCM) indicating clutch pedal position and, in some manual transmission applications, both clutch pedal position and gearshift position. PCM provides a 5-volt reference (VREF) signal to CPP and/or Park/Neutral Position (PNP) switch (on CPP signal circuit). If CPP switch is closed (indicating clutch pedal applied) and shift lever is in Neutral position, output voltage from PCM is grounded through signal return circuit to PCM and one volt or less will be present. If CPP switch (or PNP switch, or both CPP and PNP switches) is open, meaning clutch pedal is released (all systems), or shift lever is not in Neutral position (PNP switch systems), CPP input signal to PCM will be about 5 volts, indicating a load on engine. PCM uses load information for mass airflow and fuel calculations.

Crankshaft Position Sensor

Crankshaft Position (CKP) sensor is a magnetic transducer mounted on engine block, next to crankshaft pulse wheel. On all engines except 6.8L, trigger wheel has a total of 35 teeth spaced 10 degrees apart with one empty space for a missing tooth. On 6.8L, trigger wheel has a total of 39 teeth spaced 9 degrees apart and one 9 degree empty space for a missing tooth. By monitoring pulse wheel, CKP sensor indicates crankshaft position and speed information to PCM. By monitoring missing tooth, CKP sensor is also able to identify piston travel to synchronize ignition system and provide a way of tracking angular position of crankshaft relative to a fixed reference.

Cylinder Head Temperature Sensor

Cylinder Head Temperature (CHT) sensor is mounted in an aluminum cylinder head and measures metal temperature. CHT sensor is a thermistor which changes resistance proportionate to temperature changes. Resistance increases as cylinder head temperature decreases and decreases as cylinder head temperature increases. Thermistor type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying resistance of passive sensor causes a variation in total current flow.

Voltage that is dropped across a fixed resistor in series with sensor resistor determines voltage signal at PCM. This voltage signal is equal to reference voltage minus the voltage drop across the fixed resistor. If CHT sensor signal indicates an overheating condition, PCM will initiate a fail-safe cooling strategy based on information from CHT sensor. For additional information, see FAIL-SAFE COOLING STRATEGY under POWERTRAIN CONTROL SOFTWARE. Using both CHT sensor and fail-safe cooling, PCM prevents damage by allowing air cooling of engine and limp home capability.

Differential Pressure Feedback EGR Sensor

See DIFFERENTIAL PRESSURE FEEDBACK EGR SYSTEM under EGR SYSTEMS.

Engine Coolant Temperature Sensor

Engine Coolant Temperature (ECT) sensor is a thermistor device in which resistance changes with temperature. Electrical resistance of a thermistor decreases as temperature increases, and increases as temperature decreases. Varying resistance affects voltage drop across sensor terminals and provides electrical signals to PCM corresponding to temperature. Thermistor type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying resistance of passive sensor causes a variation in total current flow. Voltage that is dropped across a fixed resistor in a series with sensor resistor determines voltage signal at PCM. This voltage signal is equal to reference voltage minus voltage drop across fixed resistor. ECT measures temperature of engine coolant and is threaded into an engine coolant passage. ECT sensor is similar in construction to IAT sensor.

Engine Fuel Temperature Sensor

Engine Fuel Temperature (EFT) sensor inputs fuel temperature of fuel near fuel injectors to the PCM. EFT sensor is a thermistor device which changes resistance proportionate to temperature changes. Resistance increases as fuel temperature decreases and decreases as fuel temperature increases. Signal is used by PCM to adjust fuel injector pulse width and meter fuel to each cylinder.

Engine Oil Temperature Sensor

Engine Oil Temperature (EOT) sensor is a thermistor device which changes resistance proportionate to temperature changes. Resistance increases as engine oil temperature decreases and decreases as engine oil temperature increases. EOT sensor provides engine oil temperature to PCM. On some applications, EOT sensor input to PCM is used to initiate a soft engine shutdown. This prevents engine damage from occurring as a result of high oil temperature.

Fan Speed Sensor

See VISCTRONIC DRIVE FAN CLUTCH under OUTPUT SIGNALS.

Fuel Level Input

Fuel Level Input (FLI) is a hard wire signal input to PCM from Fuel Pump (FP) module. See description of FLI under ENHANCED EVAPORATIVE EMISSION SYSTEM under EVAPORATIVE EMISSION SYSTEMS.

Fuel Pump Monitor (With Fuel Pump Driver Module)

Fuel Pump Driver Module (FPDM) communicates diagnostic information to PCM through Fuel Pump Monitor (FPM) circuit. This information is sent by FPDM as a duty cycle signal. The 3 duty cycle signals that may be sent are listed in FUEL PUMP DRIVER MODULE DUTY CYCLE SIGNALS table. PCM uses this signal to verify FPDM is powered and able to communicate on the FPM circuit.

FUEL PUMP DRIVER MODULE DUTY CYCLE SIGNALS

Fuel Pump Monitor (Without Fuel Pump Driver Module)

The Fuel Pump Monitor (FPM) circuit is spliced into Fuel Pump Power (FP PWR) circuit and is used by PCM for diagnostic purposes. PCM sources a low current voltage down FPM circuit. With fuel pump off, voltage is pulled low by path to ground through fuel pump. With fuel pump off and FPM circuit low, PCM can verify FPM and FP PWR circuits are complete from FPM splice through fuel pump to ground. This also confirms that FP PWR or FPM circuits are not shorted to power.

With fuel pump on, voltage is supplied from fuel pump relay to FP PWR and FPM circuits. With fuel pump on and FPM circuit high, PCM can verify FP PWR circuit from fuel pump relay to FPM splice is complete. It can also verify that fuel pump relay contacts are closed and battery voltage is supplied to fuel pump relay.

Fuel Tank Pressure Sensor

See ENHANCED EVAPORATIVE EMISSION SYSTEM under FUEL EVAPORATIVE SYSTEM under EVAPORATIVE EMISSION SYSTEMS.

Fuel Rail Pressure Sensor

On Crown Victoria 4.6L NGV, Fuel Rail Pressure (FRP) sensor is a diaphragm strain gauge device in which resistance changes with pressure. (Scheme 22) Electrical resistance of a strain gauge increases as pressure increases, and decreases as pressure decreases. Varying resistance affects voltage drop across sensor terminals and provides electrical signals to PCM corresponding to pressure. Strain gauge type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying resistance of passive sensor causes a variation in total current flow. Voltage that is dropped across a fixed resistor in series with sensor resistor determines voltage signal at PCM. This voltage signal is equal to reference voltage minus voltage drop across fixed resistor.

Scheme 22

On all others, FRP sensor measures pressure of fuel near fuel injectors. (Scheme 23) This signal is used by PCM to adjust fuel injector pulse width and meter fuel to each cylinder. FRP sensor senses pressure difference between fuel rail and intake manifold. Return fuel line to fuel tank has been deleted in this type of fuel system. Differential of fuel/intake manifold pressure together with measured fuel temperature provides an indication of fuel vapors in fuel rail. Both differential pressure and temperature feedback signals are used to control fuel pump speed. Fuel pump speed sustains fuel rail pressure which preserves fuel in its liquid state. Dynamic range of fuel injectors increases because of higher rail pressure, which allows injector pulse width to decrease.

Scheme 23

Generator Load

See GENERATOR LOAD INPUT under PCM CONTROLLED CHARGING SYSTEM under MISCELLANEOUS CONTROLS.

Generator Monitor

See GENERATOR MONITOR under PCM CONTROLLED CHARGING SYSTEM under MISCELLANEOUS CONTROLS.

Heated Oxygen Sensor

Heated Oxygen Sensors (HO2S) are mounted in or right after exhaust manifold before catalytic converter (upstream HO2S), and in exhaust pipe after catalytic converter (downstream HO2S). HO2S detects presence of oxygen in exhaust gases and produces a variable voltage according to amount of oxygen detected. A high concentration of oxygen (lean air/fuel ratio) in exhaust gases produces a low voltage signal less than 0.4 volt. A low concentration of oxygen (rich air/fuel ratio) produces a high voltage signal more than 0.6 volt. HO2S provides feedback to PCM indicating air/fuel ratio in order to achieve a near stoichiometric air/fuel ratio of 14.7:1 during closed loop engine operation. HO2S generates a voltage between 0.0 and 1.1 volts.

Embedded with the sensing element is the HO2S heater. The heating element heats sensor to 1400°F (800°C). At approximately 600°F (300°C), engine can enter closed loop operation. VPWR circuit supplies voltage to heater and PCM will complete the ground when the proper conditions occur. Starting in 1998, a new HO2S heater and heater control system are installed on some vehicles. The high power heater reaches closed loop fuel control temperatures. Use of this heater requires HO2S heater control be duty cycled, to prevent damage to heater. The 6-ohm design is not interchangeable with new style 3.3-ohm heater.

Intake Air Temperature Sensor

Intake Air Temperature (IAT) sensors and integrated MAF type, are thermistor devices in which resistance changes with temperature. (Scheme 24) Electrical resistance of a thermistor decreases as temperature increases, and increases as temperature decreases. Varying resistance affects voltage drop across sensor terminals and provides electrical signals to PCM corresponding to temperature. Thermistor type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying resistance of passive sensor causes a variation in total current flow.

Scheme 24

Voltage that is dropped across a fixed resistor in a series with sensor resistor determines voltage signal at PCM. This voltage signal is equal to reference voltage minus voltage drop across fixed resistor. IAT provides air temperature information to PCM. PCM uses air temperature information as a correction factor in calculation of fuel, spark and MAF. IAT sensor provides a quicker temperature change response time than ECT or CHT sensor.

Supercharged vehicles use 2 IAT sensors. Both sensors are thermistors. However, one is located before the supercharger at air cleaner for standard OBD-II cold weather input, while the second sensor (IAT2) is located after the supercharger in intake manifold. IAT2 sensor located after supercharger provides air temperature information to PCM to control border-line spark and to help determine intercooler (charge air cooler) efficiency.

Currently 2 types of IAT2 sensors are used on supercharged vehicles. A screw in type and an integrated type, which is part of Thermal Manifold Absolute Pressure (TMAP) sensor. (Scheme 24)and (Scheme 26). TMAP sensor consists of an IAT thermistor and a Manifold Absolute Pressure (MAP) sensor. The thermistor portion of TMAP is used for IAT2 function and operates in the same manner as a non-integrated IAT2. For additional information on the TMAP, see THERMAL MANIFOLD ABSOLUTE PRESSURE SENSOR.

Intake Manifold Runner Control

See VARIABLE INDUCTION SYSTEM under AIR INDUCTION SYSTEMS.

Intake Manifold Swirl Control

See VARIABLE INDUCTION SYSTEM under AIR INDUCTION SYSTEMS.

Intake Manifold Tuning Valve

See VARIABLE INDUCTION SYSTEM under AIR INDUCTION SYSTEMS.

Knock Sensor

The Knock Sensor (KS) is a tuned accelerometer located on the engine, which converts engine vibration to an electrical signal. PCM uses this signal to determine the presence of engine knock and retards spark timing accordingly.

Mass Airflow Sensor

Mass Airflow (MAF) sensor is located between air cleaner and throttle body, or inside air cleaner assembly. MAF sensors use a hot wire sensing element to measure amount of air entering the engine. Air passing over the hot wire causes it to cool. The hot wire is maintained at 392°F (200°C) greater than ambient temperature, as measured by a constant cold wire. (Scheme 25)

The current required to maintain hot wire operating temperature is proportional to the intake air mass flow. MAF sensor outputs an analog voltage signal to PCM proportional to intake air mass. PCM uses this signal to calculate fuel injector pulse width in order to provide the desired air/fuel ratio. On some applications, MAF sensor input is used in determining transmission Electronic Pressure Control (EPC), shift and Torque Converter Clutch (TCC) scheduling.

Cougar 2.0L, Escort 2.0L 4V, Econoline, Escape, Explorer, Focus, Mountaineer, Sable, Taurus and Windstar applications use MAF sensors that have Integrated By-Pass Technology (IBT) with an integrated Intake Air Temperature (IAT) sensor.

Scheme 25

Output Shaft Speed Sensor

Output Shaft Speed (OSS) sensor provides PCM with information about rotational speed of transmission output shaft. PCM uses information to control and diagnose powertrain behavior. In some applications, OSS sensor is also used as source of monitoring vehicle speed. OSS sensor may be physically located in different places on vehicle, depending upon the specific application. Design of each OSS sensor is unique and depends on which powertrain control feature uses the information generated.

Power Steering Pressure Sensor

Power Steering Pressure (PSP) sensor monitors power steering pressure. PSP sensor voltage input to PCM will change as hydraulic pressure changes. PCM uses PSP sensor input signal to compensate for additional loads on engine by adjusting idle speed RPM, and prevents engine stall during parking maneuvers. PCM also uses PSP signal to adjust transaxle/transmission Electronic Pressure Control (EPC) pressure during increased engine load.

Power Steering Pressure Switch

Power Steering Pressure (PSP) switch monitors power steering pressure. PSP switch is normally closed and opens as pressure increases. PCM uses PSP switch input signal to compensate for additional loads on engine by adjusting idle speed RPM, and prevents engine stall during parking maneuvers. PCM also uses PSP signal to adjust transaxle/transmission Electronic Pressure Control (EPC) pressure during increased engine load.

Power Take-Off Switch

Power Take-Off (PTO) circuit is used by PCM to disable some OBD-II monitors during PTO operation. PTO switch is normally open and circuit voltage is normally low. When PTO switch is closed, battery voltage is supplied to PTO circuit, indicating an additional load condition to PCM. If an additional load condition is not reported to PCM by PTO circuit, a false DTC may be stored.

Thermal Manifold Absolute Pressure Sensor

Thermal Manifold Absolute Pressure (TMAP) sensor consists of a Manifold Absolute Pressure (MAP) sensor and an integrated thermistor. Thermistor part of TMAP sensor is currently not being used. MAP part of TMAP sensor measures intake manifold air absolute pressure. PCM uses information from TMAP sensor, Throttle Position (TP) sensor, Mass Airflow (MAF) sensor, Engine Coolant Temperature (ECT) or Cylinder Head Temperature (CHT) sensor and Crankshaft Position (CKP) sensor to determine how much exhaust gas is introduced into intake manifold through EGR system.

Scheme 26

Throttle Position Sensor

Throttle Position (TP) sensor is a rotary potentiometer sensor that provides a signal to PCM that is linearly proportional to throttle plate/shaft position. TP sensor housing has a 3-blade electrical connector that may be gold plated. The gold plating increases corrosion resistance on terminals and increases connector durability. TP sensor is mounted on throttle body and has 4 operating conditions: closed throttle (idle or deceleration), part throttle (cruise or moderate acceleration), wide open throttle and throttle angle rate. TP sensor signal affects air/fuel ratio, injector timing, idle speed, EGR flow and ignition timing. On some applications, TP sensor input is used in determining transmission Electronic Pressure Control (EPC) pressure, shift and Torque Converter Clutch (TCC) scheduling.

Transmission Control Switch

Transmission Control Switch (TCS) may also be referred to as overdrive (O/D) cancel switch. TCS position is controlled by vehicle operator. If overdrive is disengaged, O/D OFF indicator located on instrument panel, or Transmission Control Indicator Light (TCIL) located on shift lever, will illuminate.

Vehicle Speed Sensor

Vehicle Speed Sensor (VSS) is a variable reluctance or Hall Effect type sensor that generates a waveform with a frequency that is proportional to vehicle speed. When vehicle is moving slowly, sensor produces a low frequency signal. As vehicle speed increases, sensor produces a higher frequency signal. PCM uses this signal to control fuel injection, ignition timing and transaxle/transmission shift and Torque Converter Clutch (TCC) scheduling.

4x4 Mode Switch

Generic Electronic Module (GEM) provides PCM with an indication of 4x4L. This input is used to adjust transmission shift scheduling. A 5-volt module pull-up indicates 4x4H or 2WD. (Scheme 27)

Scheme 27

OUTPUT DEVICES

Note. Transmission related PCM outputs are not listed here. For a complete listing of transmission related PCM inputs, see appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS.

Vehicles are equipped with different combinations of computer controlled components. Not all components listed are used on every vehicle. For theory and operation on each output component, refer to system indicated after component.

Canister Vent Solenoid

See FUEL EVAPORATIVE SYSTEM under EVAPORATIVE EMISSION SYSTEMS.

Coil Pack

A coil in a coil pack is turned on (coil charging) by PCM, and is turned off when 2 spark plugs are fired simultaneously. Spark plugs are paired so that one spark plug fires on the compression stroke and other spark plug fires on exhaust stroke. Next time coil is fired, order is reversed and next pair of spark plugs fire according to engine firing order.

Coil On Plug

Coil On Plug (COP) ignition operates similar to a standard coil pack ignition except each spark plug has one coil per spark plug. (Scheme 28) COP has 3 different modes of operation

1. Engine Cranking During engine cranking, PCM will fire 2 spark plugs simultaneously. One spark plug will fire on compression stroke and the other spark plug fires on exhaust stroke. Both spark plugs will fire until camshaft position is identified by a successful camshaft sensor signal.
2. Engine Running Once camshaft position is identified and engine is running, only spark plug with cylinder under compression will be fired.
3. CMP Failure Mode Effects Management (CMP FMEM) During CMP FMEM, COP ignition operates similar to engine cranking mode. This allows engine to operate without requiring PCM to know if cylinder is on compression or exhaust stroke.

Scheme 28

EGR Vacuum Regulator Solenoid

See EGR SYSTEMS under EVAPORATIVE EMISSION SYSTEMS.

Electric Secondary Air Injection Pump

See ELECTRIC SECONDARY AIR INJECTION SYSTEM under SECONDARY AIR INJECTION SYSTEM.

Evaporative Emission Canister Purge Valve

Note. Evaporative Emission Canister Purge (CANP) Valve may also be referred to as Vapor Management Valve (VMV).

See FUEL EVAPORATIVE SYSTEM under EVAPORATIVE EMISSION SYSTEMS.

Fan Control

PCM monitors certain parameters such as: engine coolant temperature, vehicle speed, A/C on/off status and A/C pressure to determine engine cooling fan needs. PCM controls fan operation through Fan Control (FC) on single speed fan applications, or Low Fan Control (LFC), Medium Fan Control (MFC) and/or High Fan Control (HFC) outputs on 3 speed fan applications. Although PCM output circuits for 3-speed fans are called low, medium and high fan control, cooling fan speed is controlled by a combination of these outputs. (Scheme 29)

Scheme 29

Fuel Cap Off Indicator Light

Note. Continental, Escape, LS, Mustang, Thunderbird, Town Car and Windstar do not have a dedicated output wire from PCM to instrument cluster. PCM commands Fuel Cap Off Indicator Light (FCIL) on and off through Standard Corporate Protocol (SCP) BUS (+) and BUS (-) circuits.

FCIL is an output signal controlled by PCM and will illuminate when it is determined there is a failure in vapor management system due to fuel filler cap not being sealed properly. This would be detected by inability to pull vacuum in fuel tank, after a fueling event.

Fuel Injectors

See FUEL INJECTORS under FUEL CONTROL under FUEL SYSTEM (GASOLINE), or NG FUEL INJECTORS under FUEL CONTROL under FUEL SYSTEM (NATURAL GAS).

Fuel Pump (Applications Using Fuel Pump Relay For Fuel Pump ON/OFF Control)

Fuel Pump (FP) is a PCM output signal that is used to control electric fuel pump. With PCM power relay contacts closed, Vehicle Power (VPWR) is sent to coil of fuel pump relay. For electric fuel pump operation, PCM grounds FP circuit, which is connected to coil of fuel pump relay. This energizes coil and closes contacts of relay, sending Battery Voltage (B+) through FP PWR circuit to electric fuel pump. When ignition switch is turned to ON position, electric fuel pump runs for about one second, but is then turned off by PCM if engine rotation is not detected. For applications with 2-speed fuel pumps, a normally closed low speed fuel pump relay is wired into fuel pump ground circuit. With low speed fuel pump relay contacts in normally closed position, there is no extra resistance in ground circuit, allowing high speed operation. For low speed fuel pump operation, PCM will ground Low Fuel Pump (LFP) circuit, which opens relay contacts, causing fuel pump ground circuit to pass through a resistor. (Scheme 30) For additional fuel pump information, see FUEL DELIVERY under FUEL SYSTEM (GASOLINE).

Scheme 30

Fuel Pump Driver Module Applications & Applications With Fuel Pump Functions Incorporated In Rear Electronic Module)

Note. On LS and Thunderbird, FPDM functions are incorporated in Rear Electronic Module (REM). Fuel pump operation is same as applications using stand-alone FPDM. REM will communicate diagnostic information through Standard Corporate Protocol (SCP) BUS (+) and BUS (-) circuits, instead of using a Fuel Pump Monitor (FPM) circuit.

Fuel Pump (FP) signal is a duty cycle command sent from PCM to Fuel Pump Driver Module (FPDM). (Scheme 31) FPDM uses FP command to operate fuel pump at speed requested by PCM or to turn pump off.

Scheme 31

Generator Communication

See GENERATOR COMMUNICATION under PCM CONTROLLED CHARGING SYSTEM under MISCELLANEOUS CONTROLS.

Hydraulic Cooling Fan Drive (LS & Thunderbird Only)

Hydraulic cooling fan drive system consists of an engine driven hydraulic cooling fan pump with integral solenoid (activated by PCM), oil reservoir, hydraulic lines and hydraulic cooling fan motor. (Scheme 32) Hydraulic cooling fan motor shaft drives the cooling fan by hydraulic pressure supplied from cooling fan pump through high pressure lines. Varying voltage from PCM to hydraulic pump solenoid, opens or closes pump solenoid to change amount of fluid flow and hydraulic pressure to hydraulic cooling fan motor. When PCM increases voltage to pump solenoid (opening solenoid), it increases hydraulic cooling fan speed by increasing fluid flow and hydraulic pressure to hydraulic cooling fan motor. Hydraulic cooling fan motor is able to turn at all times due to pump solenoid current leakage, even when engine is cold.

Scheme 32

Idle Air Control Valve

See IDLE AIR CONTROL VALVE ASSEMBLY under IDLE CONTROL SYSTEM under AIR INDUCTION SYSTEMS.

See VARIABLE INDUCTION SYSTEM under AIR INDUCTION SYSTEMS.

See VARIABLE INDUCTION SYSTEM under AIR INDUCTION SYSTEMS.

See VARIABLE INDUCTION SYSTEM under AIR INDUCTION SYSTEMS.

Malfunction Indicator Light

See MALFUNCTION INDICATOR LIGHT under SELF-DIAGNOSTIC SYSTEM.

Secondary Air Injection By-Pass Solenoid

See ELECTRIC SECONDARY AIR INJECTION SYSTEM under SECONDARY AIR INJECTION SYSTEM.

Solid State Relay

See ELECTRIC SECONDARY AIR INJECTION SYSTEM under SECONDARY AIR INJECTION SYSTEM.

Thermostat Heater Control

The primary objective for the thermostat heater control is for improvement in fuel economy and thermal efficiency. The system consists of a high temperature 208°F (98°C) instead of a 194°F (90°C) thermostat that has a resistive heater within a wax element. (Scheme 33) The heater is controlled by PCM dependent on engine speed, throttle position, engine load, vehicle speed, air charge temperature, transmission oil temperature and engine coolant temperature. During low speed, low load and low air charge temperature conditions, the thermostat heater is OFF and engine is allowed to operate at an elevated coolant temperature. This should result in lower internal friction and higher thermal efficiency, both leading to improved fuel economy.

Scheme 33

During high speed, high load, high temperature conditions (air charge, transmission oil or engine coolant), PCM output is energized with a duty cycle to thermostat heater. This heats the wax and forces thermostat to rapidly open wider allowing extra coolant to flow from radiator. This will reduce coolant temperature and improve with performance demand. The heater is only capable of supplying a small amount of additional heat to wax element. It is not capable of opening thermostat alone. The thermostat is 100 percent duty cycle for short calibrated time and than duty cycle is reduced to a maximum of 70 percent ON and 30 percent OFF. Unheated, thermostat will begin to open at a coolant temperature of about 208°F (98°C), and will be fully open at 239°F (115°C). Energizing heater will reduce opening temperature to about 176°F (80°C), and the fully open temperature to 230°F (110°C).

Transmission Control Indicator Light

Transmission Control Indicator Light (TCIL) is an output signal from PCM that controls indicator light on/off function depending on engagement or disengagement of overdrive. See TRANSMISSION CONTROL SWITCH under INPUT DEVICES.

Wide Open Throttle A/C Cut-Off Relay

Note. The Wide Open Throttle A/C Cut-Off (WAC) relay may also be referred to as the A/C clutch relay.

The WAC relay is normally open. There is no direct electrical connection between A/C switch or Electronic Air Temperature Control (EATC) module and A/C clutch. On some applications, A/C request signal will be sent to PCM through Standard Corporate Protocol (SCP) BUS (+) and BUS (-) circuits. When A/C is requested, PCM will ensure all other A/C related inputs and engine components are operating correctly before grounding WAC relay output, causing voltage to be sent to A/C clutch.

Vapor Management Valve

See FUEL EVAPORATIVE SYSTEM under EVAPORATIVE EMISSION SYSTEMS.

Vehicle Speed Output

Powertrain Control Module - Vehicle Speed Output (PCM-VSO) speed signal subsystem generates vehicle speed information for vehicle's electrical/electronic modules and subsystems that require vehicle speed data. This subsystem senses transmission output shaft speed using a sensor. See OUTPUT SHAFT SPEED SENSOR or VEHICLE SPEED SENSOR under INPUT DEVICES. Vehicle speed data is processed by PCM and distributed as a hard-wired signal or as a multiplexed data message.

Key features of PCM-VSO system are to

1. Infer Vehicle Movement From Output Shaft Sensor Signal
2. Convert Transmission Output Shaft Rotational Information To Vehicle Speed Information
3. Compensate For Tire Size & Axle Ratio With A Programmed Calibration Variable
4. Utilize Transfer Case Sensor For Four Wheel Drive Applications
5. Distribute Vehicle Speed Information As A Multiplexed Message &/Or An Analog Signal

The signal from a non-contact shaft sensor mounted on transmission (OSS) or transfer case (TCSS) is sensed directly by PCM. PCM converts OSS or TCSS information to 8000 pulses per mile, based on a tire and axle ratio conversion factor. This conversion factor is programmed into PCM at time of vehicle assembly and can be reprogrammed in the field for servicing changes in tire size and axle ratio. PCM transmits computed vehicle speed and distance traveled information to all vehicle speed signal users.

VSO information can be transmitted by a hard-wired interface between vehicle speed signal user and PCM, or by speed and odometer Standard Corporate Protocol (SCP) multiplexed data messages. VSO hard-wired signal wave form is a DC square wave with a voltage level of zero to battery voltage. Typical output operating range is 2.22Hz per MPH. Multiplexed data for speed and distance data are transmitted as separate SCP messages over SCP multiplex link.

Visctronic Drive Fan Clutch

The primary purpose for Visctronic Drive Fan (VDF) clutch is to optimize fan energy (i.e. improved fuel economy) while meeting cooling performance requirements. Successful optimization will also minimize objectionable fan noise. Operation is similar to existing viscous fan clutches, except viscous fluid flow is controlled by a Pulse Width Modulated (PWM) solenoid versus a bi-metal temperature sensor on the front of the clutch. VDF consists of 3 main elements; a working chamber, a reservoir chamber, and a Fan Speed Sensor (FANSS). A fluid port valve controls fluid flow from the reservoir into the working chamber. Once viscous fluid is in the working chamber, "shearing" of fan clutch fluid will result in fan rotation.

The valve is activated via a PWM output signal from PCM. By opening and closing the fluid port valve, PCM can control approximate fan speed. Fan speed is monitored via a Hall Effect sensor and is read by PCM for closed loop operation. PCM will optimize VDF fan speed based upon Cylinder Head Temperature (CHT), Transmission Fluid Temperature (TFT), or Intake Air Temperature (IAT) sensor cooling requirements. When either of these inputs is demanding increased fan speed for vehicle cooling, PCM will monitor FANSS, and output required PWM signal to fluid port valve to control fan speed.

FUEL DELIVERY

FUEL SYSTEM IDENTIFICATION

There are 3 different types of fuel systems that are used

Returnable Fuel System

Returnable fuel system consists of a fuel tank with a reservoir, fuel pump module, fuel supply lines, fuel filter(s), Schrader/pressure test port, fuel rail, fuel injectors, and fuel pressure regulator. The following list of components and their specific operation corresponds to numbers in illustration. (Scheme 34)

1. The fuel delivery system uses Crankshaft Position (CKP) sensor to signal PCM that engine is either cranking or running.
2. The fuel pump logic is defined in Fuel System control strategy and is executed in PCM. PCM will ground fuel pump relay for one second during Key On Engine Off. During cranking, fuel pump relay is grounded as long as PCM receives a CKP signal.
3. The fuel pump relay has a primary and a secondary circuit. Primary side is controlled by PCM and secondary side provides battery voltage (B+) to fuel pump circuit when relay is energized.
4. The Inertia Fuel Shutoff (IFS) switch is used to de-energize fuel delivery secondary circuit in the event of a collision. IFS switch is a safety device that should only be reset after a thorough inspection of the vehicle (following a collision). For additional IFS information, see «INERTIA FUEL SHUTOFF SWITCH (ALL FUEL SYSTEMS)»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv__inertia-fuel-shutoff-switch-all-fuel).
5. The fuel injector is a solenoid operated valve that meters fuel flow to each cylinder. Fuel injector is opened and closed a constant number of times per crankshaft revolution. Amount of fuel is controlled by length of time fuel injector is held open. Fuel injector is normally closed and is operated by a 12-volt VPWR signal from power relay. The ground signal is controlled by PCM. For additional fuel injector information, see «FUEL INJECTORS»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv) under FUEL CONTROL.
6. A pressure test point valve (Schrader valve) is located on fuel rail. This is used to measure fuel injector supply pressure for service and diagnostic procedures. On vehicles not equipped with a Schrader valve, use Rotunda Fuel Pressure Test Kit (134-R0087) or equivalent.
7. The fuel pressure regulator is attached to fuel rail downstream of fuel injectors. It regulates fuel pressure supplied to fuel injectors. Fuel pressure regulator is a diaphragm operated relief valve. (Scheme 35) One side of diaphragm senses fuel pressure and the other side is connected to intake manifold vacuum. Fuel pressure is established by a spring preload applied to diaphragm. Balancing one side of diaphragm with manifold vacuum maintains a constant fuel pressure drop across fuel injectors. Fuel pressure is high when engine vacuum is low. Excess fuel is by-passed through fuel pressure regulator and returned through a fuel return line to fuel tank.
8. There are 4 filtering or screening devices in fuel delivery system. Fuel intake sock or screen is a fine, nylon mesh mounted on intake side of fuel pump. (Scheme 36) There is a fuel filter screen located at fuel rail side of fuel injector. A fuel filter/screen is located in the inlet side of fuel pressure regulator. The fuel filter assembly is located between fuel pump and pressure test point/Schrader valve.
9. The Fuel Pump (FP) module is a device that contains both fuel pump and fuel sender assembly. The fuel pump is located inside reservoir and supplies fuel through fuel pump module manifold to engine and fuel pump module jet pump. (Scheme 37) The fuel pump also has a discharge check valve to maintain system pressure during shutdowns and to minimize starting problems. The reservoir prevents fuel flow interruptions during extreme vehicle maneuvers with low tank fill levels.

Scheme 34

Scheme 35

Scheme 36

Scheme 37

Mechanical Returnless Fuel System

Note. Fuel rail pulse damper used on mechanical returnless fuel systems should not be confused with a fuel pressure regulator. Both are visually similar, but the fuel rail pulse damper does not regulate fuel pressure. Damper is used to reduce fuel system noise. Vacuum port on fuel rail pulse damper is connected to manifold vacuum to avoid fuel spillage if damper diaphragm ruptures.

Electronic returnless fuel system consists of a fuel tank with reservoir, fuel pump, fuel pressure regulator, fuel filter, fuel supply line, fuel rail, fuel rail pulse damper, fuel injectors, and Schrader/pressure test port. The following list of components and their specific operation corresponds to numbers in illustration. (Scheme 38)

1. The fuel delivery system is enabled during crank or running mode once PCM receives a Crankshaft Position (CKP) sensor signal.
2. The fuel pump logic is defined in the fuel system control strategy and is executed by PCM.
3. The PCM grounds fuel pump relay, which provides Vehicle Power (VPWR) to fuel pump.
4. The Inertia Fuel Shutoff (IFS) switch is used to de-energize fuel delivery secondary circuit in the event of a collision. IFS switch is a safety device that should only be reset after a thorough inspection of the vehicle (following a collision). For additional IFS information, see «INERTIA FUEL SHUTOFF SWITCH (ALL FUEL SYSTEMS)»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv__inertia-fuel-shutoff-switch-all-fuel).
5. A pressure test point valve (Schrader valve) is located on fuel rail. This is used to measure fuel injector supply pressure for service and diagnostic procedures. On vehicles not equipped with a Schrader valve, use Rotunda Fuel Pressure Test Kit (134-R0087) or equivalent.
6. The fuel rail pulse damper is located on fuel rail to reduce fuel system noise caused by pulsing of fuel injectors. The vacuum port located on damper is connected to manifold vacuum to avoid fuel spillage in the event pulse damper diaphragm were to rupture. Pulse damper should not be confused with a fuel pressure regulator.
7. The fuel injector is a solenoid-operated valve that meters fuel flow to each cylinder. Fuel injector is opened and closed a constant number of times per crankshaft revolution. Amount of fuel is controlled by length of time fuel injector is held open. Fuel injector is normally closed and is operated by a 12-volt VPWR signal from power relay. The ground signal is controlled by PCM. For additional fuel injector information, see «FUEL INJECTORS»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv) under FUEL CONTROL.
8. There are 3 filtering or screening devices in fuel delivery system. The intake sock is a fine, nylon mesh screen mounted on intake side of fuel pump. (Scheme 39) There is a fuel filter screen located at fuel rail side of fuel injector, and the fuel filter assembly is located between fuel pump and pressure test point/Schrader valve.
9. The Fuel Pump (FP) module contains fuel pump, fuel pressure regulator and fuel sender assembly. The fuel pump has a discharge check valve to maintain system pressure during shutdowns and to minimize starting problems. Fuel pressure regulator is attached to fuel pump in fuel pump module located in fuel tank. It regulates fuel pressure supplied to fuel injectors. The fuel pressure regulator is a diaphragm operated relief valve, wherein fuel pressure is established by a spring preload applied to diaphragm. Excess fuel is by-passed through regulator and returned to fuel tank.

Scheme 38

Scheme 39

Electronic Returnless Fuel System

Electronic returnless fuel system consists of a fuel tank with reservoir, fuel pump, fuel rail pressure sensor, fuel filter, fuel supply line, engine fuel temperature sensor, fuel rail, fuel injectors, and Schrader/pressure test point. The following list of components and their specific operation corresponds to numbers in illustration. (Scheme 40)

1. The fuel delivery system is enabled during crank or running mode once PCM receives a Crankshaft Position (CKP) sensor signal.
2. The fuel pump logic is defined in fuel system control strategy and is executed by PCM.
3. The PCM commands a duty cycle to Fuel Pump Driver Module (FPDM).
4. The FPDM modulates voltage to Fuel Pump (FP) to achieve proper fuel pressure. Voltage for fuel pump is supplied by power relay or FPDM power supply relay. For additional FPDM information, see «FUEL PUMP DRIVER MODULE»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv__fuel-pump-driver-module) under COMPUTERIZED ENGINE CONTROLS.
5. The Fuel Rail Pressure (FRP) sensor provides PCM with current fuel rail pressure. PCM uses this information to vary duty cycle output to FPDM to compensate for varying loads.
6. The Engine Fuel Temperature (EFT) sensor measures current fuel temperatures in fuel rail. This information is used to vary fuel pressure and avoid fuel system vaporization.
7. The fuel injector is a solenoid-operated valve that meters fuel flow to each cylinder. Fuel injector is opened and closed a constant number of times per crankshaft revolution. Amount of fuel is controlled by length of time fuel injector is held open. Fuel injector is normally closed and is operated by a 12-volt VPWR signal from power relay. The ground signal is controlled by PCM. For additional fuel injector information, see «FUEL INJECTORS»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv) under FUEL CONTROL.
8. A pressure test point valve (Schrader valve) is located on fuel rail. This is used to measure fuel injector supply pressure for service and diagnostic procedures. On vehicles not equipped with a Schrader valve, use Rotunda Fuel Pressure Test Kit (134-R0087) or equivalent.
9. There are 3 filtering or screening devices in fuel delivery system. The intake sock is a fine, nylon mesh screen mounted on intake side of fuel pump. (Scheme 41) There is a fuel filter screen located at fuel rail side of fuel injector, and the fuel filter assembly is located between fuel pump and pressure test point/Schrader valve.
10. The Fuel Pump (FP) module is a device that contains fuel pump and fuel sender assembly. The fuel pump has a discharge check valve to maintain system pressure during shutdowns and to minimize starting problems. Fuel pump is located inside reservoir and supplies fuel through fuel pump module manifold to engine and fuel pump module jet pump. The reservoir prevents fuel flow interruptions during extreme vehicle maneuvers with low tank fill levels.
11. The Inertia Fuel Shutoff (IFS) switch is used to de-energize fuel delivery secondary circuit in the event of a collision. IFS switch is a safety device that should only be reset after a thorough inspection of the vehicle (following a collision). For additional IFS information, see «INERTIA FUEL SHUTOFF SWITCH (ALL FUEL SYSTEMS)»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv__inertia-fuel-shutoff-switch-all-fuel).

Scheme 40

Scheme 41

Inertia Fuel Shutoff Switch (All Fuel Systems)

In the event of a collision or vehicle rollover, electrical contacts within the Inertia Fuel Shutoff (IFS) switch are tripped open when the internal steel ball breaks loose of the switch magnet. (Scheme 42) Once loose, the steel ball rolls up a conical ramp and makes contact with the target plate which creates an open in the electrical circuit to electric fuel pump. If the electrical circuit is opened, it is not possible to restart the vehicle until the switch is reset. A reset button is located on top of IFS switch assembly.

Scheme 42

FUEL CONTROL

Note. Fuel injectors are deposit resistant and must not be cleaned.

The PCM controls fuel injector pulse width ("on" time) to meter fuel quantity into intake ports. PCM receives inputs from engine sensors to compute fuel flow necessary to maintain correct air/fuel ratio throughout entire engine operating range. Injector pulse width is the only controlled variable in fuel delivery system.

Each cylinder has a solenoid-operated injector that sprays fuel toward the back of each intake valve. Fuel injector nozzles are solenoid-operated valves, which meter and atomize fuel delivered to engine. Each injector receives battery voltage through an ignition switch circuit. The PCM controlled ground circuit is used to complete the circuit and energize the injector.

Injector bodies consist of solenoid actuated pintle and needle valve assembly. (Scheme 43) Injector flow orifice is fixed and fuel pressure at injector tip is constant. Fuel flow to engine is regulated according to length of time solenoid is energized. Atomized spray pattern is obtained by shape of pintle.

Scheme 43

Natural Gas (NG) fuel system consists of fuel tank(s), fuel shutoff valve assemblies, fuel supply lines, fuel filter, manual shutoff valve(s), service (Schrader) valve, fuel injection supply manifold and fuel pressure regulator. The following list of components and their specific operation corresponds to numbers in illustration. (Scheme 44)

1. The Crankshaft Position (CKP) sensor is used to signal PCM that engine is either cranking or running.
2. The fuel shutoff valve logic is defined in Fuel System control strategy and is executed in PCM. PCM will ground fuel pump relay for one second during Key On Engine Off (KOEO). During cranking, fuel pump relay is grounded as long as PCM receives a signal from CKP.
3. The fuel pump relay has a primary and a secondary circuit. The primary side is controlled by PCM and secondary side provides battery voltage (B+) to fuel shutoff valve circuit when relay is energized.
4. The Inertia Fuel Shutoff (IFS) switch is used to de-energize fuel delivery secondary circuit in the event of a collision. IFS switch is a safety device that should only be reset after a thorough inspection of the vehicle (following a collision). For additional IFS information, see «INERTIA FUEL SHUTOFF SWITCH (ALL FUEL SYSTEMS)»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv__inertia-fuel-shutoff-switch-all-fuel).
5. The fuel injector is used to meter natural gas to each combustion cylinder. Although NG fuel injector appears very similar to some gasoline fuel injectors, it is unique. Flow capacity of this fuel injector is 6-12 times as large as various gasoline fuel injectors. (Scheme 45) For additional NG fuel injector information, see «NG FUEL INJECTORS»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv__ng-fuel-injectors) under FUEL CONTROL.
6. The fuel tank shutoff solenoid valve is located in fuel tank. The solenoid valves are on the same circuit as fuel pump and utilize the same Inertia Fuel Shutoff (IFS) switch as gasoline models. For additional fuel tank shutoff solenoid valve information, see «FUEL TANK SHUTOFF VALVE»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv__fuel-tank-shutoff-valve).
7. The high pressure fuel filter is used to protect engine fuel system components. A natural gas coalescing and particulate filter is located on high pressure side of fuel system just prior to fuel pressure regulator. Filter is part of regulator assembly. Filter can be disassembled to service the element. Drain plug on bottom of filter housing can be removed to drain any accumulated water.
8. The fuel pressure regulator is located on frame rail. Fuel pressure regulator used on NG vehicles is a single-staged pressure reducing regulator which expands natural gas from storage pressures of 200-3,000 psi (1379-20,685 kPa) to engine fuel pressures of 105-125 psi (724-862 kPa). For additional NG fuel pressure regulator information, see «NG FUEL PRESSURE REGULATOR»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv__ng-fuel-pressure-regulator).
9. The fuel rail shutoff valve is a normally closed solenoid actuated valve that opens when terminal No. 80 is grounded by PCM. The valve isolates fuel injectors from fuel line pressure when engine is not operating. The fuel rail shutoff valve is wired in parallel with fuel tank shutoff solenoid valves. For additional fuel rail shutoff valve information, see «FUEL RAIL SHUTOFF VALVE»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv__fuel-rail-shutoff-valve).

Scheme 44

Scheme 45

Fueling Connector

The flange assembly is designed for 3000 psi (20,685 kPa) service pressure and is the refueling connection to fill vehicle. The assembly is mounted behind fuel filler door and attached to fuel filler housing, similar to a gasoline vehicle. This assembly consists of an NGVP1 type receptacle with a 150-micron filter (which can be serviced), a spring loaded check valve to allow filling of vehicle and a manually opened bypass to provide safe venting of fuel system. The vehicle is refueled by attaching fuel station fill nozzle to receptacle and locking into place.

Fuel Lines & Fittings

A fuel line assembly consists of flexible hose and/or stainless steel seamless tubing, end fittings and tube nuts. The hose is a conductive polytetrafluoroethylene (PTFE) liner reinforced with a stainless steel wire braided covering. The fittings are inserted into hose ends and crimped into place. The stainless steel tubing contains end fittings which are brazed to the tube. There are high pressure fuel lines that are identified by either 1/4-inch or 3/8-inch outer diameter, and a low pressure fuel line identified by a 1/2-inch outer diameter. The low pressure fuel line has a quick-connect at one end for connection to fuel rail. The other fittings used on natural gas vehicle to connect fuel components are SAE "O" ring face seal tube fittings. There are 2 end types: an "O" ring face seal end and a straight thread end. On tee and elbow fittings, a washer and a positionable nut are provided to aid in orientation of the fitting.

Fuel Rail

The fuel rail distributes low pressure fuel from chassis supply line to each fuel injector. Fuel pressure at top of each fuel injector is maintained within 1 percent of other fuel injectors at all times, done by nearly symmetric flow paths. The fuel rail is also designed to have minimal flow restriction by increasing cross-sectional flow area and reducing flow path length. The fuel rail contains several other components that perform crucial functions. (Scheme 45) These include

1. Injection Pressure Sensor Measures the pressure of fuel near fuel injectors. This signal is used by PCM to adjust fuel injector pulse width and meter fuel to each cylinder.
2. Engine Fuel Temperature Sensor Measures pressure of fuel near fuel injectors. This signal is used by PCM to adjust fuel injector pulse width and meter fuel to each cylinder.
3. Low Pressure Solenoid Shutoff Valve Isolates fuel rail from upstream fuel system when engine is OFF. This minimizes the amount of fuel available to flow through fuel injectors when engine is off or leak from a damaged fuel rail during and after a crash. The valve is controlled by PCM fuel shutoff valve circuit and contains an inertia switch. The valve is only on for one second after a key-on or whenever CKP signals are being received by PCM.
4. Schrader/Service Valve Provides a service port to low pressure fuel system. This valve is needed to relieve pressure in system before and during service. This valve could also be used to monitor pressure near injectors during diagnostic procedures.

Fuel Rail Shutoff Valve

The fuel rail shutoff valve is a normally closed valve that opens when terminal No. 80 is grounded by PCM. (Scheme 46) Resistance of the fuel rail shutoff valve coil is 11 ohms. When ignition switch is in ON position, power relay is turned on. Power relay provides power to PCM and control side of fuel shutoff valve relay. Relay provides voltage to fuel rail valve. If ignition switch is not in START position, PCM will close fuel rail shutoff valve after one second. PCM will open valve, along with the tank valve(s), to provide fuel while cranking. The valve will remain open when engine is running unless IFS switch is "tripped".

Scheme 46

Fuel Tank Shutoff Valve

The fuel tank shutoff valve is located in fuel tank(s). (Scheme 47) When ignition switch is in OFF position, fuel tank shutoff valves are closed and fuel in the tanks is isolated. During refueling, fuel tank shutoff valve acts as a check valve and allows flow due to pressure differential between fuel being added from fill station and fuel in the tank.

The fuel tank shutoff valve internal solenoid valves also have capability of being manually locked down. While servicing vehicle, if it becomes necessary to remove the fuel tank, lock down feature provides an added measure of safety.

The fuel tank shutoff valve has an internal Canadian Gas Association (CGA) type 9 fusible link pressure relief device that senses internal fuel tank gas temperature. Fuel tank is vented to the atmosphere when internal fuel tank gas temperature reaches 217°F (199°C) and melts fusible link. The escaping gas is vented through a vent line.

Scheme 47

Inertia Fuel Shutoff Switch

See INERTIA FUEL SHUTOFF SWITCH (ALL FUEL SYSTEMS) under FUEL SYSTEM (GASOLINE).

NG Fuel Pressure Regulator

Fuel pressure regulator contains a 275 psi (1896 kPa) check valve that protects the low pressure system. When natural gas expands, fuel temperature decreases. Causing an extreme drop in temperature; to as low as -160°F (-177°C) . To prevent damaging synthetic fuel system components or causing water vapor within fuel to condense, engine coolant is routed through pressure regulator to warm fuel before it expands. The regulator has an internal thermostat to control flow of engine coolant, preventing overheating and thinning of fuel which could cause lean combustion. When coolant temperature increases to about 100°F (82°C), regulator thermostat closes and outlet coolant flow is restricted.

See NATURAL GAS VEHICLE MODULE under COMPUTERIZED ENGINE CONTROLS.

NG Fuel Injectors

Powertrain Control Module (PCM) controls fuel injector pulse width ("on" time) to meter fuel quantity into intake ports. The PCM receives inputs from engine sensors to compute fuel flow necessary to maintain correct air/fuel ratio throughout entire engine operating range. Injector pulse width is the only controlled variable in fuel delivery system.

Each cylinder has a solenoid-operated injector that sprays fuel toward the back of each intake valve. Fuel injector nozzles are solenoid-operated valves which meter and atomize fuel delivered to engine. Each injector is normally closed and receives 12 volts VPWR from power relay. The PCM controlled ground circuit is used to complete the circuit and energize the injector.

Flow capacity of natural gas fuel injectors is 6-12 times greater than typical gasoline fuel injectors. Also, injector resistance (4.6 ohms) is less than gasoline fuel injectors (14.5 ohms). To accommodate the lower resistance, a Fuel Injector Driver Module (also referred to as Natural Gas (NG) module, is used to convert PCM fuel injector driver signal to the signal required by fuel injector.

Note. Ignition timing is controlled by the Powertrain Control Module (PCM) and is not adjustable. DO NOT attempt to check base timing as false readings will result.

Description

Integrated Electronic Ignition (EI) system consists of a Crankshaft Position (CKP) sensor, coil pack(s), wiring and PCM. Coil On Plug (COP) integrated EI system uses a separate coil for each spark plug and each coil is mounted directly onto spark plug. COP integrated EI system eliminates need for spark plug wires but does require input from Camshaft Position (CMP) sensor. The following list of components and their specific operation corresponds to numbers in illustration. (Scheme 48)

1. The CKP sensor is used to indicate crankshaft position and speed by sensing a missing tooth on a pulse wheel mounted to crankshaft. The CMP sensor is used by COP Integrated EI System to identify top dead center of compression of cylinder No. 1 to synchronize firing of individual coils. For additional CKP or CMP sensor information, see «CAMSHAFT POSITION SENSOR»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv__camshaft-position-sensor) or «CRANKSHAFT POSITION SENSOR»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv__crankshaft-position-sensor) under INPUT DEVICES under COMPUTERIZED ENGINE CONTROLS.
2. The PCM uses CKP signal to calculate a spark target and then fires coil pack(s) to that target shown. (Scheme 49) The PCM uses CMP sensor on COP Integrated EI Systems to identify top dead center of compression of cylinder No. 1 to synchronize firing of individual coils.
3. The coils and coil packs receive their signal from PCM to fire at a calculated spark target. Each coil within pack fires 2 spark plugs at the same time. The plugs are paired so that as one fires during compression stroke, the other fires during exhaust stroke. The next time the coil is fired, the situation is reversed. The COP system fires only one spark plug per coil and only on compression stroke. PCM acts as an electronic switch to ground in the coil primary circuit. When the switch is closed, battery positive voltage (B+) applied to coil primary circuit builds a magnetic field around primary coil. When the switch opens, power is interrupted and primary field collapses inducing high voltage in secondary coil windings and the spark plug is fired. A kickback voltage spike occurs when primary field collapses and the PCM uses this voltage spike to generate an Ignition Diagnostic Monitor (IDM) signal. IDM communicates information by pulse width modulation in PCM.
4. The PCM processes CKP signal and uses it to drive tachometer as Clean Tach Output (CTO) signal.

Scheme 48

Scheme 49

Coil Pack System

The EI system consists of a CKP sensor, coil pack(s), related wiring and PCM. The CKP sensor is used by PCM to indicate crankshaft position and speed by sensing a missing tooth on a pulse wheel mounted on front of crankshaft. The coil pack receives the signal from the PCM to fire at a calculated spark target. Each coil within the pack fires 2 spark plugs at the same time.

The plugs are paired so one plug is fired on the compression stroke, and the other plug fires the mating cylinder, which is on the exhaust stroke. On the next cycle, firing is reversed. On 6-tower coil pack applications the matched cylinder pairs are: No. 1 and 5, No. 2 and 6, and No. 3 and 4. (Scheme 50)and (Scheme 51).

On single 4-tower coil pack applications (4-cylinder), the matched cylinder pairs are No. 1 and 4, and No. 2 and 3. (Scheme 52)and (Scheme 53). On dual 4-tower coil pack applications (8-cylinder), the matched cylinder pairs are No. 1 and 6, No. 3 and 5, No. 4 and 7, and No. 2 and 8. (Scheme 53)

The PCM acts as an electronic switch to ground in the coil primary circuit. When the switch is closed, positive battery voltage applied to the coil primary circuit builds a magnetic field around the primary coil. When the switch opens, power is interrupted and the primary field collapses inducing high voltage in the secondary coil winding and the spark plug is fired.

Scheme 50

Scheme 51

Scheme 52

Scheme 53

Coil On Plug System

Individual COPs are mounted directly on spark plugs. (Scheme 28) CKP sensor is used by PCM to indicate crankshaft position and speed by sensing a missing tooth on a pulse wheel mounted on front of crankshaft. The CMP sensor is used by PCM to identify when piston No. 1 is at Top Dead Center (TDC) of compression stroke. This signal is used to synchronize firing of individual coils.

The individual coils receive their signal from PCM to fire at a calculated spark target. Only one coil is fired at a time and only on compression stroke. PCM acts as an electronic switch to ground individual coil primary circuit. When the switch is closed, battery voltage applied to coil primary circuit builds a magnetic field around primary coil. When the switch opens, power is interrupted and primary field collapses, inducing high voltage in secondary coil winding and spark plug is fired. For additional COP information, see COIL ON PLUG under OUTPUT SIGNALS under COMPUTERIZED ENGINE CONTROLS.

Variable Cam Timing (VCT) system allows exhaust cam to advance and retard at varying engine speeds. This is to reduce exhaust emissions and increase fuel economy. As exhaust cam retards in relation to crankshaft position, residual exhaust gases are left in combustion chamber. Residual gases cool combustion chamber and are inert when mixed with incoming fresh charge of fuel and air. This results in better fuel economy and lower Nitrogen Oxides (NOx) and Hydrocarbons (HC) emitted from the engine. VCT system eliminates the need for an Exhaust Gas Recirculation (EGR) system.

VCT system applies only to Escort and Focus 2.0L ZETEC (VIN 3) engines. VCT system consists of control solenoid, 5-tooth pulse ring (4+1) on exhaust camshaft, Intake Air Temperature (IAT) sensor, Engine Coolant Temperature (ECT) sensor, Camshaft Position (CMP) sensor, Mass Air Flow (MAF) sensor, Crankshaft Position (CKP) sensor and PCM. The following list of components and their specific operation corresponds to numbers in illustration. (Scheme 54)

1. PCM receives input signals from IAT sensor, ECT sensor, CMP sensor, MAF sensor and CKP sensor for determining operating conditions of the engine.
2. VCT system is enabled by PCM when the proper conditions are met. PCM disables VCT system if a fault is detected.
3. PCM calculates relative cam position using CMP sensor and data from (4+1) pulse ring mounted on exhaust camshaft. Relative cam position is calculated by measuring time between the rising edge of Profile Ignition Pickup (PIP) and the falling edge of VCT pulse.
4. PCM continually calculates a cam position error value based on the difference between desired and actual position and a duty cycle is commanded for VCT solenoid valve. Engine oil is allowed to flow to VCT unit. For additional VCT solenoid valve information, see «VARIABLE CAM TIMING SOLENOID VALVE»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv__variable-cam-timing-solenoid-valve) .
5. Oil flows to either side of the piston chamber changing a linear motion from piston to a rotation motion from the helical mechanism in VCT unit. During closed loop, PCM outputs a revised duty cycle to VCT solenoid valve to correct for cam position error. For additional VCT unit information, see «VARIABLE CAM TIMING UNIT ASSEMBLY»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv__variable-cam-timing-unit-assembly) .

Scheme 54

Variable Cam Timing Solenoid Valve

Variable Cam Timing (VCT) solenoid valve is an integral part of VCT system. (Scheme 55) VCT solenoid valve controls flow of engine oil to VCT unit assembly. As PCM duty cycles the solenoid valve, oil is allowed to flow to VCT unit assembly and advance or retard cam timing.

Scheme 55

Variable Cam Timing Unit Assembly

Variable Cam Timing (VCT) unit assembly is coupled to camshaft through a helical spline in the VCT unit chamber. When flow of oil is shifted from one side of the chamber to the other, differential change in oil pressure forces piston to move linearly along the axis of the camshaft. This linear motion is translated into rotational camshaft motion through the helical spline coupling. A spring installed in the chamber is designed to hold camshaft in minimum overlap position (5 degrees) when oil pressure is too low to maintain adequate position control. Camshaft is allowed to rotate up to 30 degrees.

CATALYST SYSTEM

The catalytic converter and exhaust systems work together to control the release of harmful engine exhaust emissions into the atmosphere. Engine exhaust gas consists mainly of Nitrogen (N), Carbon Dioxide (CO 2 ) and water vapor (H 2 O). However, it also contains Carbon Monoxide (CO), Oxides of Nitrogen (NO x ), Hydrogen (H), and various unburned Hydrocarbons (HCs). CO, NO x , and HCs are major air pollutants, and their emission into the atmosphere must be controlled. The exhaust system generally consists of an exhaust manifold, front exhaust pipe, upstream Heated Oxygen Sensor (HO2S), rear exhaust pipe, downstream HO2S, a muffler and an exhaust tailpipe. The catalytic converter is installed between front and rear exhaust pipes. Catalytic converter efficiency is monitored by the OBD-II system. For additional OBD-II Monitor information, see DIAGNOSTIC MONITORS under COMPUTERIZED ENGINE CONTROLS.

Catalytic Converter

A catalyst is a material that remains unchanged when it initiates and increases the speed of a chemical reaction. A catalyst will also enable a chemical reaction to occur at a lower temperature. The catalytic converter assists in controlling the concentration of exhaust gas products released to the atmosphere. It contains a catalyst in the form of a specially treated ceramic honeycomb structure saturated with catalytically active precious metals. As exhaust gases come in contact with the catalyst, they are changed into mostly harmless products. The catalyst initiates and speeds up heat producing chemical reactions of the exhaust gas components so they are used up as much as possible. For additional 3-Way Catalytic (TWC) converter information, see 3-WAY CATALYTIC CONVERTER .

Light Off Catalyst

As the catalyst heats up, converter efficiency rises rapidly. The point at which conversion efficiency exceeds 50 percent is called catalyst light off. For most catalysts this point occurs at 475-575°F (246-301°C). A fast light catalyst is a 3-Way Catalyst (TWC), that is located as close to exhaust manifold as possible. Because light off catalyst is located close to exhaust manifold it will light off faster and reduce emissions quicker than the catalyst located under vehicle. Once catalyst lights off, the catalyst will quickly reach maximum conversion efficiency.

3-Way Catalytic Converter

The 3-way Catalytic (TWC) converter contains either Platinum (Pt) and Rhodium (Rh), or Palladium (Pd) and Rhodium (Rh). TWC converter catalyzes oxidation reactions of unburned HCs and CO and reduction reaction of NOx. The 3-way conversion can be best accomplished by always operating engine air fuel/ratio at or close to stoichiometry (14.7:1). For additional stoichiometry information, see 3-WAY CATALYST CONVERSION EFFICIENCY .

3-Way Catalyst Conversion Efficiency

A TWC requires a stoichiometric fuel ratio, 14.7 pounds of air to one pound of fuel (14.7:1), for high conversion efficiency. In order to achieve these high efficiencies, air/fuel ratio must be tightly controlled with a narrow window of stoichiometry. Deviations outside of this window will greatly decrease conversion efficiency. (Scheme 56) For example, a RICH mixture will decrease HC and CO conversion efficiency, while a LEAN mixture will decrease NOx conversion efficiency.

Scheme 56

EXHAUST SYSTEM

The purpose of the exhaust system is to convey engine emissions from exhaust manifold to atmosphere. Engine exhaust emissions are directed from engine exhaust manifold to catalytic converter through front exhaust pipe. A Heated Oxygen Sensor (HO2S) is mounted on the front exhaust pipe before catalyst. Catalytic converter reduces concentration of Carbon Monoxide (CO), unburned Hydrocarbons (HCs) and Oxides of Nitrogen (NOx) in exhaust emissions to an acceptable level. Reduced exhaust emissions are directed from catalytic converter to a muffler through rear exhaust pipe. Another HO2S is mounted on rear exhaust pipe. Exhaust emissions are then directed to atmosphere through an exhaust tailpipe.

Hardware

The downstream HO2S may be located after light off catalyst or underbody catalyst. Underbody catalyst may be in-line with light off catalyst, or underbody catalyst may be common to 2 light off catalysts, forming a "Y" pipe configuration.

Exhaust Manifold & Runners

Exhaust manifold runners collect exhaust gases from engine cylinders. The number of exhaust manifolds and exhaust manifold runners depends on engine configuration and number of cylinders.

Exhaust Pipes

Exhaust pipes are usually treated during manufacturing with an anti-corrosive coating agent to increase the life of the product. The pipes serve as guides for flow of exhaust gases from engine exhaust manifold through catalytic converter and muffler.

Upstream & Downstream Heated Oxygen Sensors

Heated Oxygen Sensors (HO2S) provide PCM with voltage and frequency information related to oxygen content of exhaust gas. For additional HO2S information, see HEATED OXYGEN SENSOR under PCM INPUTS under COMPUTERIZED ENGINE CONTROLS. In addition to providing PCM with indications of how rich or lean the engine is operating, upstream HO2S signal serves as an input to HO2S monitor. Downstream HO2S signal is an input to Catalyst Efficiency Monitor. For additional Catalyst Efficiency Monitor information, see CATALYST EFFICIENCY MONITOR DESCRIPTION under DIAGNOSTIC MONITORS under COMPUTERIZED ENGINE CONTROLS.

Muffler

Mufflers are usually treated during manufacturing with an anti-corrosive coating agent to increase the life of the product. The muffler reduces noise levels produced by engine, and it also reduces noise produced by exhaust gases as they travel from catalytic converter to atmosphere.

FUEL EVAPORATIVE SYSTEMS

The Evaporative Emission (EVAP) system prevents fuel vapor build-up in the fuel tank. Fuel vapor trapped in fuel tank is vented through the vapor valve assembly on top of fuel tank. Fuel vapors leave the valve assembly through a single vapor line and continue on to the EVAP canister for storage until vapors are purged into the engine for burning. EVAP canister is located in engine compartment, in rear of vehicle near luggage compartment or underneath vehicle along the frame rail. There are 2 different types of EVAP systems that may be used

1. «ENHANCED EVAPORATIVE EMISSION SYSTEM»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv__enhanced-evaporative-emission-system)
2. «ON-BOARD REFUELING VAPOR RECOVERY EVAP SYSTEM»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv__on-board-refueling-vapor-recovery-evap-system)

ENHANCED EVAPORATIVE EMISSION SYSTEM

The enhanced Evaporative Emission (EVAP) running loss system consists of a fuel tank, fuel filler cap, fuel tank mounted or in-line fuel vapor control valve, fuel vapor vent valve, EVAP canister, fuel tank mounted or fuel pump mounted or in-line Fuel Tank Pressure (FTP) sensor, EVAP canister purge valve, intake manifold hose assembly, Canister Vent (CV) solenoid, PCM and connecting wires and fuel vapor hoses. The following list of components and their specific operation corresponds to numbers in illustration. (Scheme 57)

1. Enhanced EVAP running loss system uses inputs from Engine Coolant Temperature (ECT) sensor, Intake Air Temperature (IAT) sensor, Throttle Position (TP) sensor, Mass Airflow (MAF) sensor, Vehicle Speed Sensor (VSS) and Fuel Tank Pressure (FTP) sensor to provide information about engine operating conditions to PCM. The Fuel Level Input (FLI) and FTP sensor signals are used by PCM to determine activation of EVAP Monitor based on presence of fuel vapor or fuel sloshing.
2. PCM calculates a variable duty cycle based on desired amount of purge vapor flow to intake manifold for a given engine condition. PCM can then output the duty cycle to solenoid on EVAP canister purge valve. PCM uses Enhanced EVAP system inputs to evacuate system, using EVAP canister purge valve, CV solenoid to seal Enhanced EVAP system from atmosphere, and uses FTP sensor to observe total vacuum lost for a period of time.
3. Canister Vent (CV) solenoid seals EVAP canister from atmospheric pressure. (Scheme 58) This allows EVAP canister purge valve to obtain fuel tank target vacuum during EVAP Leak Check Monitor. For additional EVAP Leak Check Monitor information, see «EVAPORATIVE EMISSION LEAK CHECK MONITOR»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv__evaporative-emission-leak-check-monitor) under DIAGNOSTIC MONITORS under COMPUTERIZED ENGINE CONTROLS.
4. PCM outputs a variable duty cycle signal (between zero and 100 percent) to solenoid on EVAP canister purge valve. For additional EVAP canister purge valve information, see «EVAP CANISTER PURGE VALVE»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv__evap-canister-purge-valve).
5. Fuel Tank Pressure (FTP) sensor is used to measure fuel tank pressure during EVAP Monitor Running Monitor test. FTP sensor is also used to control excessive fuel tank pressure by forcing the system to purge. (Scheme 59)and (Scheme 60).
6. The fuel tank mounted fuel vapor vent valve assembly, fuel tank mounted fuel vapor control valve (or remote fuel vapor control valve) are used in Enhanced EVAP system to control flow of fuel vapor entering engine. All of these valves also prevent fuel tank overfilling during refueling operation and prevent liquid fuel from entering EVAP canister and EVAP canister purge valve under any vehicle altitude, handling or rollover condition. The liquid/vapor fuel discriminator is part of fuel vapor control valve assembly on Escort and Focus models.
7. The fuel filler cap is used to prevent fuel spill and close evaporative emission/fuel system to atmosphere. Some vehicles may have a Fuel Cap Off Indicator Light (FCIL) in instrument cluster which will illuminate when there is a failure in vapor management system that may be due to fuel filler cap not being sealed. For additional FCIL information, see «FUEL CAP OFF INDICATOR LIGHT»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv__fuel-cap-off-indicator-light) under OUTPUT SIGNALS under COMPUTERIZED ENGINE CONTROLS.

The Enhanced EVAP system, including all fuel vapor hoses, can be checked when a leak is detected by PCM. This can be done by pressurizing system using Rotunda Evaporative Emission Tester Kit (134-00056) or equivalent, and leak (frequency) detector included with kit.

Scheme 57

Scheme 58

Scheme 59

Scheme 60

EVAP Canister Purge Valve

EVAP canister purge valve is part of Enhanced EVAP system that is controlled by PCM. (Scheme 61)and (Scheme 62). This valve controls flow of vapors (purging) from EVAP canister to intake manifold during various engine operating modes. EVAP canister purge valve is a normally closed valve.

Scheme 61

Scheme 62

ON-BOARD REFUELING VAPOR RECOVERY EVAP SYSTEM

On-Board Refueling Vapor Recovery (ORVR) EVAP system components consist of fuel tank, fuel filler cap, fuel filler pipe check valve/flapper valve, Fuel Tank Pressure (FTP) sensor, fuel vapor vent valve(s), EVAP canister(s), EVAP canister purge valve, Canister Vent (CV) solenoid, related wiring and fuel vapor hoses. For component location and application, refer to illustrations. (Scheme 63)- (Scheme 70). Component descriptions are as follows

1. Fuel Filler Pipe Check Valve The fuel filler pipe check valve on Continental, Crown Victoria, Grand Marquis, LS, Mustang, Sable, Taurus and Town Car is located inside fuel filler pipe. Purpose of check valve is to prevent liquid fuel from re-entering the fuel filler pipe during refueling or during a vehicle rollover condition.
2. Fuel Filler Pipe Flapper Valve The fuel filler pipe flapper valve on Contour, Cougar, Escort, Focus and Mystique, is located inside fuel filler pipe. Purpose of flapper valve is to minimize fuel flow from backing up into fuel filler pipe. Flapper valve is not a positive seal to fuel tank.
3. Fill Limit Vent Valve Assembly The fill limit valve assembly on Contour, Cougar, Escort, Focus, LS and Mystique controls fuel tank volume and prevents fuel from entering the vent tube in a vehicle rollover condition. The fill limit valve consists of a vent tube, vapor seal (which has an "O" ring on both ends) and a check valve which consists of a float with a spring assembly.
4. Fuel Vapor Vent Valve Fuel vapor vent valve assembly is mounted on top of fuel tank and is used to control flow of fuel vapor entering the fuel tank vapor delivery line to the EVAP canister. The head valve portion of the fuel vapor vent valve prevents fuel tank from overfilling during refueling. The fuel vapor vent valve also has a spring supported float that prevents liquid fuel from entering fuel tank vapor delivery line under severe handling or a vehicle rollover condition.
5. Fuel Vapor Control Valve (Fuel Tank Mounted) The fuel vapor control valve on Continental, Crown Victoria, Grand Marquis, Mustang, Sable, Taurus and Town Car is used for preventing liquid fuel from entering the EVAP canister and EVAP canister purge valve.
6. EVAP Canister Vapors from fuel tank are stored in EVAP canister. With engine running at an RPM higher than idle, vapors are purged from EVAP canister back into the engine for combustion.

Scheme 63

Scheme 64

Scheme 65

Scheme 66

Scheme 67

Scheme 68

Scheme 69

Scheme 70

POSITIVE CRANKCASE VENTILATION

Positive Crankcase Ventilation (PCV) System cycles crankcase gases back through engine where they are burned. PCV valve regulates amount of ventilating air and blow-by gas to intake manifold and prevents backfire from traveling into crankcase. PCV valve should be mounted in a vertical position. On some applications, PCV system is connected to EVAP emission system. Refer to Vehicle Emission Control Information (VECI) underhood decal.

The Secondary Air Injection (AIR) system controls emissions during first 20-120 seconds of engine operation by forcing air downstream into exhaust manifolds to oxidize hydrocarbons and carbon monoxide created by running rich at start up.

ELECTRIC SECONDARY AIR INJECTION SYSTEM

Electric Secondary Air Injection (AIR) system consists of an Electric AIR Pump (EAP), single or dual combination check air injection diverter (AIR diverter) valve(s), an AIR by-pass solenoid, a solid state relay, PCM, wiring and vacuum hoses. The following list of components and their specific operation corresponds to numbers in illustration. (Scheme 71)

1. PCM requires Engine Coolant Temperature (ECT), Intake Air Temperature (IAT) and Crankshaft Position (CKP) inputs to initiate secondary air injection function.
2. When engine is started, strategy will determine when to enable Electric Air Pump (EAP). After a 5-10 second delay, PCM signals solid state relay and AIR by-pass solenoid to begin system operation. Once catalyst is lit-off, PCM then signals solid state relay to stop EAP operation and to close AIR by-pass solenoid from supplying vacuum to AIR diverter valve(s). For additional AIR by-pass solenoid or AIR diverter valve information, see «AIR BY-PASS SOLENOID»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv__air-by-pass-solenoid) or «AIR DIVERTER VALVE»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv__air-diverter-valve).
3. Solid state relay provides start-up signal and will switch high current required to operate EAP. Input control to solid state relay comes from PCM. (Scheme 72)
4. AIR by-pass solenoid applies a vacuum to AIR diverter valve(s) causing it to open and to allow air to flow into exhaust manifolds.
5. Vacuum check valve controls vacuum bleed-off to solenoid.
6. Function of splash cap, if equipped, is to provide EAP with a source of dry air.
7. EAP delivers required amount of air to control emissions during engine operation. Air is forced into exhaust manifolds to oxidize hydrocarbons and carbon monoxide created by running rich at start up. For additional EAP information, see «ELECTRIC AIR PUMP»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv__electric-air-pump).

Scheme 71

Scheme 72

Scheme 73

AIR By-Pass Solenoid

Secondary AIR by-pass solenoid is used by PCM to control vacuum to secondary AIR diverter valve. AIR by-pass solenoid is a normally closed solenoid. AIR by-pass solenoid also has a filtered vent feature to permit vacuum release. (Scheme 73)

AIR Diverter Valve

The secondary air injection diverter (AIR diverter) valve is used with Electric Air Pump (EAP) to provide on/off control of air to exhaust manifold and catalytic converter. (Scheme 73) When EAP is on and vacuum is supplied to AIR diverter valve, air passes integral check valve disk. When EAP is off, and vacuum is removed from AIR diverter valve, integral check valve disk is held on the seat and stops air from being drawn into exhaust system and prevents backflow of exhaust into secondary air injection system.

Electric AIR Pump

Electric AIR Pump (EAP) provides pressurized air to secondary air injection system. EAP functions independently of RPM and is controlled by PCM. EAP is used for short periods of time. Delivery of air is dependent on amount of system backpressure and system voltage. Inlet system of EAP incorporates a non-serviceable filter and splash cap which helps to guard against dirt and water. (Scheme 73)

EGR SYSTEMS

Note. The self-diagnostic system monitors EGR system performance and sets a Diagnostic Trouble Code (DTC) if self-test requirements are not obtained.

Exhaust Gas Recirculation (EGR) system controls oxides of nitrogen (NOx) emissions. Small amounts of exhaust gases are recirculated back into combustion chamber to be reburned with air/fuel charge. There are 2 different types of EGR systems that may be used

1. «DIFFERENTIAL PRESSURE FEEDBACK EGR SYSTEM»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv__differential-pressure-feedback-egr-system)
2. «ELECTRIC MOTOR EGR SYSTEM»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv__electric-egr-motor-system)

DIFFERENTIAL PRESSURE FEEDBACK EGR SYSTEM

Differential Pressure Feedback (DPFE) EGR system consists of a DPFE EGR sensor, EGR vacuum regulator solenoid, EGR valve, orifice tube assembly and Powertrain Control Module (PCM). The following list of components and their specific operation corresponds to numbers in illustration. (Scheme 74)

1. DPFE EGR system receives signals from Engine Coolant Temperature (ECT) sensor, Intake Air Temperature (IAT) sensor, Throttle Position (TP) sensor, Mass Airflow (MAF) sensor and Crankshaft Position (CKP) sensor to provide information on engine operating conditions to PCM. Engine must be warm, stable and running at a moderate load and engine speed (RPM) before EGR system is activated. PCM deactivates EGR during idle, extended Wide Open Throttle (WOT), or whenever a failure is detected in an EGR component or EGR required input.
2. PCM calculates desired amount of EGR flow for a given engine condition. It then determines desired pressure drop across metering orifice required to achieve that flow and outputs corresponding signal to EGR vacuum regulator solenoid.
3. EGR vacuum regulator solenoid receives a variable duty cycle signal between 0-100 percent. The higher the duty cycle, the more vacuum the solenoid diverts to EGR valve. For additional EGR vacuum regulator solenoid information, see «EGR VACUUM REGULATOR SOLENOID»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv).
4. The increase in vacuum acting on EGR valve diaphragm overcomes valve spring and begins to lift EGR valve pintle off its seat, causing exhaust gas to flow into intake manifold.
5. Exhaust gas flowing through EGR valve must first pass through EGR metering orifice (orifice tube). With one side of orifice exposed to exhaust backpressure and other to intake manifold, a pressure drop is created across orifice whenever there is EGR flow. When EGR valve closes, there is no longer flow across metering orifice and pressure on both sides of orifice is the same. PCM constantly targets a desired pressure drop across metering orifice to achieve desired EGR flow. For additional orifice tube assembly information, see «ORIFICE TUBE ASSEMBLY»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv__orifice-tube-assembly).
6. DPFE EGR sensor measures actual pressure drop across metering orifice and relays a proportional voltage signal between 0-5 volts to PCM. (Scheme 75) PCM uses this feedback signal to correct for any errors in achieving desired EGR flow. For additional DPFE EGR sensor information, see «REMOTE MOUNTED DIFFERENTIAL PRESSURE FEEDBACK EGR SENSOR»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv__differential-pressure-feedback-egr-sensor-remote) or «TUBE MOUNTED DIFFERENTIAL PRESSURE FEEDBACK EGR SENSOR»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv__differential-pressure-feedback-egr-sensor-tube).

Scheme 74

Scheme 75

Differential Pressure Feedback EGR Sensor (Remote Mounted)

Differential Pressure Feedback (DPFE) EGR sensor is a ceramic, capacitive type pressure transducer that monitors differential pressure across a metering orifice located in orifice tube assembly. DPFE EGR sensor receives this signal through 2 hoses referred to as downstream pressure hose (REF), and upstream pressure hose (HI). HI and REF hose connections are marked on aluminum DPFE EGR sensor housing for identification. Note that HI uses a larger diameter hose. DPFE EGR sensor outputs a voltage proportional to pressure drop across metering orifice and supplies it to PCM as EGR flow rate feedback. (Scheme 76)

Scheme 76

Differential Pressure Feedback EGR Sensor (Tube Mounted)

Tube mounted DPFE EGR sensor is identical in operation as remote mounted larger metal or plastic DPFE sensors and uses a one volt offset. HI and REF hose connections are marked on underside of sensor. (Scheme 77)

Scheme 77

Vacuum regulator solenoid is an electromagnetic device used to regulate vacuum supply to the EGR valve. EGR vacuum regulator solenoid contains a coil which magnetically controls the position of a disk to regulate the vacuum. As the duty cycle to coil increases, vacuum signal passed through the EGR vacuum regulator solenoid to the EGR valve also increases. Vacuum not directed to the EGR is vented to atmosphere. At zero percent duty cycle (no electrical signal applied), EGR vacuum regulator solenoid allows some vacuum to pass, but not enough to open EGR valve.

EGR Valve

EGR valve in the DPFE EGR system is a conventional, vacuum actuated EGR valve. The valve increases or decreases flow of exhaust gas recirculation. As vacuum applied to EGR valve diaphragm overcomes spring force, valve begins to open. As vacuum signal weakens, at 1.6 in. Hg (5.4 kPa) or less, spring force closes valve. EGR valve is fully open at about 4.5 in. Hg (15 kPa). Since EGR flow requirement varies greatly, providing service specifications on flow rate is impractical. The OBD-II system monitors EGR valve function and triggers a DTC if test criteria is not met. EGR valve flow rate is not measured directly as part of field diagnostic procedures.

Orifice Tube Assembly

Orifice tube assembly is the section of tubing connecting exhaust system to intake manifold. Orifice tube provides a flow path for exhaust gas to intake manifold. The orifice tube contains a metering orifice and 2 pressure pick-up tubes. (Scheme 78) The metering orifice creates a measurable pressure drop across it as EGR valve opens and closes. The pressure differential across the orifice is picked up by DPFE EGR sensor which provides feedback to PCM.

Scheme 78

ELECTRIC EGR MOTOR SYSTEM

Electric EGR (EEGR) motor/valve system uses exhaust gas recirculation to control Oxides of Nitrogen (NOx) emissions just like vacuum operated systems. The difference is the way in which exhaust gas is controlled. Advantages to this type of system are

1. EEGR valve is activated by an electric stepper motor not a vacuum motor. It is located at rear of engine block.
2. No vacuum diaphragm is used.
3. No DPFE sensor is used.
4. No Orifice Tube Assembly is used.
5. No EGR vacuum regulator solenoid is used.
6. A new MAP sensor is used. A TMAP is used, but temperature function is not used at this time. TMAP is located on top of valve cover.
7. Engine coolant is routed through the assembly, extending durability of electric motor.

EEGR system consists of an electric EGR motor/valve integrated assembly, a PCM, TMAP sensor and connecting wiring. The following list of components and their specific operation corresponds to numbers in illustration. (Scheme 79)

1. EEGR system receives signals from Engine Coolant Temperature (ECT) or Cylinder Head Temperature (CHT) sensor, Throttle Position (TP) sensor, Mass Airflow (MAF) sensor, Crankshaft Position (CKP) sensor and Thermal Manifold Absolute Pressure (TMAP) sensor to provide information on engine operating conditions to PCM. Engine must be warm, stable and running at a moderate load and engine speed (RPM) before EEGR system is activated. PCM will deactivate EGR during idle, extended Wide Open Throttle (WOT), or whenever a failure is detected in an EEGR component or EGR required input.
2. PCM calculates desired amount of EGR for a given set of engine operating conditions.
3. PCM in turn will output signals to EEGR motor to move (advance or retract) a certain number of discrete steps. Electric stepper motor will directly actuate EGR valve, independent of engine vacuum. EGR valve is commanded from 0-52 discrete increments or "steps" to move EGR valve from a fully closed to full or partially open position. The position of EGR valve determines EGR flow.
4. TMAP sensor is used to measure variations in manifold pressure as exhaust gas recirculation is introduced into intake manifold. Variations in EGR being used will correlate to TMAP signal. Increasing EGR will increase manifold pressure values.

EEGR valve is a water cooled motor/valve assembly. (Scheme 80)and (Scheme 81). The motor is commanded to move in 52 discrete steps as it acts directly on EGR valve. Position of valve determines rate of EGR flow. The built in spring works to close valve against motor opening force.

Scheme 79

Scheme 80

Scheme 81

SELF-DIAGNOSTIC SYSTEM

Note. All systems have self-diagnostic capabilities. For information on procedures for entering self-test modes and reading diagnostic trouble codes, see SELF-DIAGNOSTICS - EEC-V - CNG & GASOLINE article.

Malfunction Indicator Light (MIL) alerts the driver that PCM has detected an OBD-II emission related component or system fault. When this occurs, an OBD-II DTC will be set. MIL is located on instrument cluster and is labeled CHECK ENGINE, SERVICE ENGINE SOON or uses an ISO standard engine symbol. (Scheme 82) Power is supplied to MIL whenever ignition switch is in RUN or START position. MIL will remain ON in RUN or START mode as a bulb check during instrument cluster proveout for about 4 seconds. MIL will remain on after bulb check for the following reasons

1. PCM illuminates MIL for an emission related concern and a DTC will be present.
2. Instrument cluster will illuminate MIL if PCM does not send a control message to instrument cluster.
3. PCM is operating in Hardware Limited Operation Strategy (HLOS). See «HARDWARE LIMITED OPERATION STRATEGY»(/ford/explorer-sport-trac/i-2000-2005/remont/theory-operation/#engine-controls-theory-operation-gasoline-ngv__hardware-limited-operation-strategy) under POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS.
4. MIL circuit is shorted to ground.

If MIL remains off (during bulb check), possible causes are; bulb is damaged or MIL circuit is open. To turn off the MIL after a repair, a reset command from scan tool must be sent, or 3 consecutive drive cycles must be completed without a fault. For any MIL concern, go to appropriate TROUBLE SHOOTING - NO CODES article. If MIL blinks at a steady rate, a severe misfire condition could possibly exist. If MIL blinks erratically, an intermittent open in B+ circuit to bulb or an intermittent short to ground in MIL circuit may exist. Also, PCM can reset while cranking if battery voltage is low.

Scheme 82

PCM controlled charging system provides many additional benefits over integral generator regulator system. First benefit is improved battery life. In an integral generator regulator system, regulator set point is established by a temperature sensor in the regulator which estimates battery temperature. With PCM controlled generator, regulator voltage set points are determined by PCM and communicated to regulator via generator communication line. PCM uses a calibratable algorithm to estimate battery temperature. Improving battery temperature will reduce battery damage caused by over and undercharging.

Second benefit is improved engine performance. Whenever PCM senses a Wide Open Throttle (WOT), PCM will momentarily lower regulator voltage set point. This reduces torque load of the generator on engine and improves acceleration. PCM has a calibratable time limit on this reduced voltage feature. This prevents the generator output from being cut back for an extended WOT period, which could cause battery discharge.

Third benefit is improved idle stability. In response to PCM generator communication signal, regulator uses a generator monitor signal to provide feedback to PCM. Generator monitor signal provides PCM with charging system information. If the charging system receives a transient electrical load which would normally affect idle stability, the PCM is notified. Because PCM can anticipate additional loads, actions can be taken to minimize idle sag. PCM can choose to either reduce regulator set point or increase engine idle speed.

Fourth benefit is reduced cranking efforts. PCM can reduce mechanical load on starter by initially commanding a low voltage set point. This may improve start times.

If PCM detects a charging system error, charge indicator will illuminate. Charge indicator will illuminate if PCM fails to see a signal on generator monitor line for a time period greater than 500 milliseconds. This command will also be used to indicate over-voltage conditions detected by generator.

Each time ignition switch is turned to RUN position, cluster will perform a bulb check by illuminating charge indicator. PCM will send a low voltage command if charging system is functioning properly. This message should be sent 250-450 milliseconds after ignition switch is turned to RUN position. If a low voltage command is not received by cluster, cluster will continue to illuminate charge indicator indefinitely.

PCM controlled charging system provides improved battery life and improved engine performance. PCM controlled generator regulator voltage set point is determined by PCM and communicated to the regulator by the Generator Communication (GEN COM) circuit. PCM will use a calibratable algorithm to estimate battery temperature, reducing damage to battery by overcharging or undercharging. At Wide Open Throttle (WOT), PCM will momentarily lower the regulator voltage set point, reducing torque load on engine and improving acceleration. PCM has a calibratable time limit on the reduced voltage feature to prevent decreased generator output for an extended WOT period, which may cause battery discharge.

Generator Load Input (GLI) circuit is used by PCM to determine generator load on engine. As generator load increases, PCM will adjust idle speed accordingly. This helps reduce idle surges due to switching high current loads. GLI signal is sent to PCM from voltage regulator/generator. GLI signal is a variable frequency duty cycle. Normal operating frequency is 40-250 Hz. Normal signal DC voltage (referenced to ground) is between 1.5 volts (low generator load) and 10.5 volts (high generator load).

The regulator uses a Generator Monitor (GEN MON) signal to provide feedback to Powertrain Control Module (PCM) with charging system information. GEN MON signal lets PCM know when the charging system receives a transient electrical load which would normally affect idle stability. Because PCM can anticipate additional loads, PCM can choose to reduce regulator set point or increase engine idle speed, both of which are calibratable features. Charge indicator will be illuminated if PCM fails to see a signal on generator monitor line for a time period greater than 500 milliseconds. This telltale command will also be used to indicate over-voltage conditions detected by PCM controlled generator.

See also:
• INPUT DEVICES
• OUTPUT SIGNALS
• POWERTRAIN CONTROL MODULE LOCATION
• KEEP ALIVE RANDOM ACCESS MEMORY
• FLASH ELECTRICALLY ERASABLE PROGRAMMABLE READ ONLY MEMORY
• FAILURE MODE EFFECTS MANAGEMENT
• FAIL-SAFE COOLING STRATEGY
• HARDWARE LIMITED OPERATION STRATEGY
• VISCTRONIC DRIVE FAN CLUTCH
• CYLINDER HEAD TEMPERATURE SENSOR
• STANDARD CORPORATE PROTOCOL
• CATALYST EFFICIENCY MONITOR - SWITCH RATIO METHOD (1996-2002)
• CATALYST EFFICIENCY MONITOR - INDEX RATIO METHOD (SOME 2001-LATER)
• COMPREHENSIVE COMPONENT MONITOR
• WIDE OPEN THROTTLE A/C CUT-OFF RELAY
• DIFFERENTIAL PRESSURE FEEDBACK EGR SYSTEM
• ENHANCED EVAPORATIVE EMISSION SYSTEM
• FUEL PUMP
• THERMAL MANIFOLD ABSOLUTE PRESSURE SENSOR
• FUEL EVAPORATIVE SYSTEM
• EGR SYSTEMS
• ELECTRIC SECONDARY AIR INJECTION SYSTEM
• NG FUEL INJECTORS
• FUEL DELIVERY
• IDLE AIR CONTROL VALVE ASSEMBLY
• TRANSMISSION CONTROL SWITCH
• OUTPUT SHAFT SPEED SENSOR
• VEHICLE SPEED SENSOR
• RETURNABLE FUEL SYSTEM
• MECHANICAL RETURNLESS FUEL SYSTEM
• ELECTRONIC RETURNLESS FUEL SYSTEM
• INERTIA FUEL SHUTOFF SWITCH (ALL FUEL SYSTEMS)
• FUEL PUMP DRIVER MODULE
• FUEL TANK SHUTOFF VALVE
• NG FUEL PRESSURE REGULATOR
• FUEL RAIL SHUTOFF VALVE
• NATURAL GAS VEHICLE MODULE
• CAMSHAFT POSITION SENSOR
• CRANKSHAFT POSITION SENSOR
• COIL ON PLUG
• VARIABLE CAM TIMING SOLENOID VALVE
• VARIABLE CAM TIMING UNIT ASSEMBLY
• DIAGNOSTIC MONITORS
• 3-WAY CATALYTIC CONVERTER
• 3-WAY CATALYST CONVERSION EFFICIENCY
• HEATED OXYGEN SENSOR
• CATALYST EFFICIENCY MONITOR DESCRIPTION
• ON-BOARD REFUELING VAPOR RECOVERY EVAP SYSTEM
• EVAPORATIVE EMISSION LEAK CHECK MONITOR
• EVAP CANISTER PURGE VALVE
• FUEL CAP OFF INDICATOR LIGHT
• AIR BY-PASS SOLENOID
• AIR DIVERTER VALVE
• ELECTRIC AIR PUMP
• ELECTRIC MOTOR EGR SYSTEM
• ORIFICE TUBE ASSEMBLY
• REMOTE MOUNTED DIFFERENTIAL PRESSURE FEEDBACK EGR SENSOR
• TUBE MOUNTED DIFFERENTIAL PRESSURE FEEDBACK EGR SENSOR