Engine Controls - Theory & Operation - Cng, Flex-Fuel & Gasoline: Other Ford Econoline E250

VECI Decal

Each vehicle has a VECI decal (Scheme 198) containing emission control information that applies specifically to the vehicle and engine. The specifications on the decal are critical to servicing emissions systems.

Scheme 198

Engine/Evaporative Emission System Information

Manufacturers must use a standardized system for identifying their individual engine families. The system described below was developed by the Environmental Protection Agency (EPA) in 1991 to meet new regulatory requirements for 1994 and later model years.

The ENGINE FAMILY GROUP and EVAPORATIVE FAMILY name consists of 12 characters each.

Both the engine family group and the evaporative family name are listed in the box on the emission decal as indicated in (Scheme 199), in the area marked as engine evaporative family information. The first line contains engine size and the 12-character engine family group. The second line contains the 12-character evaporative family name information. Both the engine family group and the evaporative family name are specific to the vehicle. Please refer to the Engine Family Group and the Evaporative Family Name work sheet for decoding information.

Scheme 199

Scheme 200

Scheme 201

VECI Acronym Definitions

ALVW-Adjusted Loaded Vehicle Weight, (Curb Weight + GVWR) /2.

Averaging Bank/Trade-Used for Nox Credits on Heavy Duty Trucks Only.

BBL-Barrel.

CALIFORNIA ARB-California Air Resource Board.

CARB-California Air Resource Board.

CARB LEV-Low Emission Vehicle.

CARB TLEV-Transitional Low Emission Vehicle.

CARB ULEV-Ultra Low Emission Vehicle.

CARB ZEV-Zero Emission Vehicle.

CPI-Central Port Injection.

CI-Cylinder Injection.

CNG-Compressed Natural Gas.

EPA-Environmental.

EVAP-Evaporative Emissions.

GVW-Gross Vehicle Weight.

GVWR-Gross Vehicle Weight Rating, Curb weight plus payload.

HHDE-Heavy Heavy Duty Engine.

HHDDE-Heavy Heavy Duty Diesel Engine.

MHDE-Medium Heavy Duty Diesel Engine.

MPI-Multi Port Injection.

LDDT-Light Duty Diesel Truck categories.

LDT-Light Duty Truck (gasoline) categories based on weight as defined in the table.

LDV-Light Duty Vehicle, generally passenger cars and light trucks under 6000 pounds GVWR.

LHDE-Light Heavy Duty Engine (several weight categories).

LVW-Loaded Vehicle Weight, curb weight plus 300 pounds.

MDT-Medium Duty Truck categories based on weight as defined in the table.

MDV-Medium Duty Vehicle.

MHDE-Medium Heavy Duty Engine.

MY-Model Year.

NCP-Non Compliance Penalty.

OBD-On-Board Diagnostic.

ORVR-On-Board Refueling Vapor Recovery.

PC-Passenger Car.

SI-Sequential Injection.

SULEV-Super Ultra Low Emission Vehicle.

Tier 0-California and Federal regulations effective prior to Tier 1 phase in dates.

Tier 1-California regulations beginning in 1993 model year and Federal regulations beginning in 1994 model year.

TBI-Throttle Body Injection.

LEV-Low Emission Vehicle.

ZEV-Zero Emission Vehicle.

ULEV-Ultra Low Emission Vehicle.

ILEV-Inherently Low Emission Vehicle.

Catalyst Efficiency Monitor

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

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

All vehicles utilize an FTP-based (Federal Test Procedure) catalyst monitor. This simply means that the catalyst monitor must run during a standard FTP emission test. This differs from the 20-second steady state catalyst monitor used in 1994 through some 1996 vehicles. Currently, two slightly different versions of the catalyst monitor are utilized - the Switch Ratio method and the Index Ratio method. Beginning with the 2001 model year and beyond, both versions will continue to be used in subsequent model years.

Switch Ratio Method

1. In order to assess catalyst oxygen storage, the monitor counts front and rear HO2S switches during part throttle, close-loop fuel condition after the engine is warmed-up and inferred catalyst temperature is within limits. Front switches are accumulated in up to nine different air mass regions or cells although three air mass regions is typical. Rear switches are counted in a single cell for all air mass regions. When the required number of front switches has accumulated in each cell, the total number of rear switches is divided by the total number of front switches to compute a switch ratio. A switch ratio near 0.0 indicates high oxygen storage capacity; hence high HC efficiency. A switch ratio near 1.0 indicates low oxygen storage capacity; hence low HC efficiency. If the actual switch ratio exceeds a calibrated threshold switch ratio, the catalyst is considered failed. 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 the Catalyst Efficiency Monitor. Typical Switch Ratio Monitor Entry Conditions: Part throttle with no rapid throttle transients Minimum 330 seconds since start-up at 70° F (21°C) Engine coolant temperature is between 170° F (76.6°C) and 230°F (110°C) Intake air temperature is between 20°F (-6°C) and 180°F (82°C) Engine load greater than 10% Time since entering close loop is 30 seconds Vehicle speed is between 5 and 70 mph (8 and 112 km/h) Inferred Catalyst Mid-bed Temperature of 900° F (482° C) Mass air flow is between 1 and 5 lbs/min Fuel level greater than 15% EGR is between 1 and 12%
2. The DTCs associated with this test are DTC P0420 (Bank 1 or Y-pipe system) and P0430 (Bank 2). Because an Exponentially Weighted Moving Average algorithm is used for malfunction determination, up to six driving cycles may be required to illuminate the MIL during normal customer driving. If KAM is reset or the battery is disconnected, a malfunction will illuminate the MIL in 2 drive cycles.

Index Ratio Method

1. In order to assess catalyst oxygen storage, the catalyst monitor counts front HO2S switches during part throttle, closed-loop fuel conditions after the engine is warmed-up and inferred catalyst temperature is within limits. Front switches are accumulated in up to three different air mass regions or cells. While catalyst monitoring entry conditions are being met, the front and rear HO2S signal lengths are continually being calculated. When the required number of front switches has accumulated in each cell, the total signal length of the rear HO2S is divided by the total signal length of the front HO2S to compute a catalyst index ratio. An index ratio near 0.0 indicates high oxygen storage capacity; hence high HC efficiency. A switch ratio near 1.0 indicates low oxygen storage capacity; hence low HC efficiency. If the actual index ratio exceeds the threshold index ratio, the catalyst is considered failed. 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 the Catalyst Efficiency Monitor. Typical Index Ratio Monitor Entry Conditions: Minimum 330 seconds since start-up at 70° F (21°C) Engine coolant temperature is between 170° F (76.6°C) and 230°F (110°C) Intake air temperature is between 20°F (-6°C) and 180°F (82°C) Time since entering close loop is 30 seconds Inferred Rear HO2S sensor temperature of 900° F (482° C) EGR is between 1 and 12% Part throttle, maximum rate of change 0.2 volts/0.050 sec Vehicle speed is between 5 and 70 mph (8 and 112 km/h) Fuel level greater than 15% First Air Flow Cell Engine RPM 1,000 to 1,300 rpm. Engine load 15 to 35%. Inferred catalyst temp. 850° F (454° C) to 1,200° F (649° C). Number of front O2 switches: 50. Second Air Flow Cell Engine RPM 1,200 to 1,500 rpm. Engine load 20 to 35%. Inferred catalyst temp. 900° F (482° C) to 1,250° F (677° C). Number of front O2 switches: 70. Third Air Flow Cell Engine RPM 1,300 to 1,600 rpm. Engine load 20 to 40%. Inferred catalyst temp. 950° F (510° C) to 1,300° F (704° C). Number of front O2 switches: 30.
2. The DTCs associated with this test are DTC P0420 (Bank 1 or Y-pipe system) and P0430 (Bank 2). Because an Exponentially Weighted Moving Average algorithm is used for malfunction determination, up to six driving cycles may be required to illuminate the MIL during normal customer driving. If KAM is reset or the battery is disconnected, a malfunction will illuminate the MIL in 2 drive cycles.

Comprehensive Component Monitor

The Comprehensive Component Monitor (CCM) monitors for malfunctions in any powertrain electronic component or circuit that provides input or output signals to the 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 the hardware, function, and type of signal. For example, analog inputs such as Throttle Position or Engine Coolant Temperature are typically checked for opens, shorts and out-of-range values. This type of monitoring is performed continuously. Some digital inputs like Vehicle Speed or Crankshaft Position rely on rationality checks - checking to see if the input value makes sense at the 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 the Idle Air Control 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 the secondary side of the relay. Some outputs are also monitored for proper function by observing the reaction of the control system to a given change in the output command. An Idle Air Control solenoid can be functionally tested by monitoring idle rpm relative to the target idle rpm. Some tests can only be performed under appropriate test conditions; for example, transmission shift solenoids can only be tested when the PCM commands a shift.

The following is an example of some of the input and output components monitored by the CCM. The components monitor may belong to the engine, ignition, transmissions, 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), 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.
3. CCM is enabled after the engine starts and is running. A Diagnostic Trouble Code (DTC) is stored in Keep Alive Memory and the MIL is illuminated after two driving cycles when a malfunction is detected. Many of the CCM tests are also performed during on demand self-test.

Scheme 202

Evaporative Emission (EVAP) Leak Check Monitor

The Evaporative Emission (EVAP) Leak Check Monitor is an on-board strategy designed to detect a leak from a hole (opening) equal to or greater than 0.508 mm (0.020 inch) in the Enhanced EVAP system. The proper function of the individual components of the Enhanced EVAP system as well as its ability to flow fuel vapor to the engine is also examined. The EVAP Leak Check Monitor relies on the individual components of the Enhanced EVAP system to apply vacuum to the fuel tank and then seal the entire Enhanced EVAP system from atmosphere. The fuel tank pressure is then monitored to determine the total vacuum lost (bleed-up) for a calibrated period of time. Inputs from the 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 the EVAP Leak Check Monitor.

Note. During the EVAP Leak Check Monitor Repair Verification Drive Cycle, clearing the continuous diagnostic trouble codes (DTCs) and resetting the emission monitors information in the powertrain control module (PCM) will bypass the minimum soak time required to complete the monitor. The EVAP Leak Check Monitor will not run if the key is turned off after clearing the continuous DTCs and resetting the emission monitors information in the PCM. The EVAP Leak Check Monitor will not run if a MAF sensor failure is indicated. The EVAP Leak Check Monitor will not initiate until the heated oxygen sensor (HO2S) monitor has completed.

The EVAP Leak Check Monitor is executed by the individual components of the Enhanced EVAP system as follows

1. The EVAP canister purge valve is used to control the flow of vacuum from the engine and create a target vacuum on the fuel tank.
2. The Canister Vent (CV) solenoid is used to seal the EVAP system from atmosphere. It is closed by the PCM (100% duty cycle) which then allows the EVAP canister purge valve to obtain the target vacuum on the fuel tank.
3. The fuel tank pressure (FTP) sensor will be used by the EVAP Leak Check Monitor to determine if the target vacuum on the fuel tank is being reached to perform the leak check. Some vehicle applications with the EVAP Leak Check Monitor use a remote in-line FTP sensor. Once the target vacuum on the fuel tank is achieved, the change in fuel tank vacuum for a calibrated period of time will determine if a leak exists.
4. If the initial target vacuum cannot be reached, DTC P0455 (gross leak detected) will be set. The EVAP Leak Check Monitor will abort and not continue with the leak check portion of the test. For some vehicle applications: If the initial target vacuum cannot be reached after a refueling event and the purge vapor flow is excessive, DTC P0457 (fuel cap off) is set. If the initial target vacuum cannot be reached and the purge flow is too small, DTC P1443 (no purge flow condition) is set. If the initial target vacuum is exceeded, a system flow fault exists and DTC P1450 (unable to bleed-up fuel tank vacuum) is set. The EVAP Leak Check Monitor will abort and not continue with the leak check portion of the test. If the target vacuum is obtained on the fuel tank, the change in the fuel tank vacuum (bleed-up) will be calculated for a calibrated period of time. The calculated change in fuel tank vacuum will be compared to a calibrated threshold for a leak from a hole (opening) of 1.016 mm (0.040 inch) in the Enhanced EVAP system. If the calculated bleed-up is less than the calibrated threshold, the Enhanced EVAP system passes. If the calibrated bleed-up exceeds the calibrated threshold, the test will abort and rerun the test up to three times. If the bleed-up threshold is still being exceeded after three tests, a vapor generation check must be performed before DTC P0442 (small leak detected) will be set. This is accomplished by returning the Enhanced EVAP system to atmospheric pressure by closing the EVAP canister purge valve and opening the CV solenoid. Once the FTP sensor observes the fuel tank is at atmospheric pressure, the CV solenoid closes and seals the 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 the fuel tank pressure build-up exceeds the threshold, the leak test results are invalid due to vapor generation. The EVAP Leak Check Monitor will attempt to retest again. If the fuel tank pressure build-up does not exceed the threshold, the leak test results are valid and DTC P0442 will be set.
5. If the 1.016 mm (0.40 inch) test passes, the test time is extended to allow the 0.508 mm (0.020 inch) test to run. The calculated change in fuel vacuum over the extended time is compared to a calibrated threshold for a leak from a 0.508 mm (0.020 inch) hole (opening). If the calculated bleed-up exceeds the calibrated threshold, vapor generation is run. If vapor generation passes (no vapor generation), an internal flag is set in the PCM to run a 0.508 mm (0.020 inch) test at idle (vehicle stopped). On the next start following a long engine off period, the Enhanced EVAP system will be sealed and evacuated for the first 10 minutes of operation. If the appropriate conditions are met, a 0.508 mm (0.020 inch) leak check is conducted at idle. If the test at idles fails, a DTC P0456 will be set. There is no vapor generation test with the idle test. 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.
6. The 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 the Comprehensive Component Monitor (CCM).

Scheme 203

Exhaust Gas Recirculation (EGR) System Monitor - Delta Pressure Feedback (DPFE) EGR and EGR System Module (ESM) EGR

The EGR System Monitor is an on-board strategy designed to test the integrity and flow characteristics of the EGR system. The monitor is activated during EGR system operation and after certain base engine conditions are satisfied. Input from the ECT, CHT, IAT, TP and CKP sensors is required to activate the monitor. Once activated, the EGR System Monitor will perform each of the tests described below during the engine modes and conditions indicated. Some of the EGR System Monitor tests are also performed during on demand self-test.

Note. The Delta Pressure Feedback EGR (DPFE) sensor, EGR Vacuum Regulator (EVR) solenoid, Manifold Absolute Pressure (MAP) sensor and the EGR valve itself are integrated into one unit in the ESM EGR assembly. The ESM is not serviceable. If any one component fails within the ESM, the entire ESM assembly must be replaced.

1. The Delta Pressure Feedback EGR sensor and circuit are continuously tested for opens and shorts. The monitor looks for the DPFE circuit voltage to exceed the maximum or minimum allowable limits. The DTCs associated with this test are DTCs P0405 or P1400 and P0406 or P1401.
2. The EVR solenoid is continuously tested for opens and shorts. The monitor looks for an EVR circuit voltage that is inconsistent with the EVR circuit commanded output state. The DTC associated with this test is DTC P0403 or P1409.
3. The 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 the DPFE circuit voltage at idle to the DPFE circuit voltage stored during key on engine off to determine if EGR flow is present at idle. The DTC associated with this test is DTC P0402.
4. The DPFE sensor hoses are tested once per drive cycle for disconnect and plugging. The test is performed with EGR valve closed and during a period of acceleration. The PCM will momentarily command the EGR valve closed. The monitor looks for the DPFE sensor voltage to be inconsistent for a no flow voltage. A voltage increase or decrease during acceleration while the EGR valve is closed may indicate a fault with a signal hose during this test. The DTCs associated with this test are DTC P1405 and P1406.
5. The EGR flow rate test is performed during a steady state when engine speed and load are moderate and EVR duty cycle is high. The monitor compares the actual 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 the EGR system to fail. The 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 two consecutive drive cycles.

Scheme 204

Scheme 205

Electric Exhaust Gas Recirculation (EEGR) System Monitor

The Electric or "Stepper" Motor EGR System Monitor is an on-board strategy designed to test the integrity and flow characteristics of the EGR system. The monitor is activated during EGR system operation and after certain base engine conditions are satisfied. Input from the ECT or CHT, IAT, TP, CKP, MAF, and MAP sensors is required to activate the EGR System Monitor. Once activated, the EGR System Monitor will perform each of the tests described below during the engine modes and conditions indicated. Some of the EGR System Monitor tests are also performed during on demand self-test

The Electric EGR Monitor consists of an electrical and functional test that checks the stepper motor and the EEGR system for proper flow. The PCM controls the EEGR valve by commanding from 0 to 52 discreet increments or "steps" to get the valve from fully closed to fully open. The stepper motor electrical test is a continuous check of the four electric stepper motor coils and circuits to the PCM. A malfunction is indicated if an open circuit, short to power or short to ground has occurred in one or more of the stepper motor coils or circuits for a calibrated period of time. If a malfunction has been detected, the EEGR system will be disabled, setting the KOER, and Continuous P0403 DTC. Additional monitoring will be suspended for the remainder of the drive cycle, or until the next engine startup.

After the vehicle has warmed up and normal EEGR flow rates are being commanded by the PCM, the EEGR flow check is performed. The flow test is performed once per drive cycle when a minimum amount of exhaust gas is requested and the remaining entry conditions required to initiate the test are satisfied. If a malfunction is detected, the EEGR system as well as the EEGR monitor is disabled until the next engine startup.

The EEGR flow test is done by observing the behavior of two different values: MAP - the analog MAP sensor reading, and inferred MAP - calculated from the Mass Air Flow Sensor, throttle position, rpm, etc. During normal, steady-state operating conditions, EEGR is intrusively commanded ON to a specified percentage. Then, EEGR is commanded OFF. If the EEGR system is working properly, there is a significant difference in both the observed and the calculated values of MAP, between the EGR-ON and the EGR-OFF states.

When flow test entry conditions have been satisfied, EEGR is commanded to flow at a calibrated test rate (about 10%). At this time, the value of MAP is recorded (EGR-ON MAP). The value of inferred MAP EGR-ON IMAP is also recorded. Next the EEGR is commanded off (0%). Again, the value of MAP is recorded (EGR-OFF MAP). The value of EGR-OFF IMAP is also recorded. Typically, seven such ON/OFF samples are taken. After all the samples have been taken, the average EGR-ON MAP, EGR-ON IMAP, EGR-OFF MAP and EGR-OFF IMAP values are stored.

Next, the difference between the EGR-ON and EGR-OFF value is calculated

1. MAP-delta = EGR-ON MAP - EGR-OFF MAP (analog MAP)
2. IMAP-delta = EGR-ON IMAP - EGR-OFF IMAP (inferred MAP)

If the sum of MAP-delta and IMAP-delta exceeds a maximum threshold or falls below a minimum threshold, a P0400 (high or low flow malfunction) is registered.

As an additional check, if the EGR-ON MAP exceeds a maximum threshold (BARO, a calibrated value), DTC P0400 (low flow) is set. This check is performed to detect reduced EGR flow on systems where the MAP pickup point is not located in the intake manifold, but is located just upstream of the EEGR valve in the EEGR delivery tube.

Note. BARO is inferred at engine startup using the KOEO MAP sensor reading. It is updated during high, part-throttle or high rpm engine operation.

If the inferred ambient temperature is less than -7° C (20° F), greater than 54° C (130° F), or the altitude is greater than 8,000 feet (BARO < 22.5 " Hg), the EEGR flow test cannot be reliably done. In these conditions, the EEGR flow test is suspended and a timer starts to accumulate the time in these conditions. When the vehicle leaves these extreme conditions, the timer starts decrementing, and if conditions permit, will attempt to complete the EGR flow monitor. If the timer reaches 500 seconds, the EEGR flow test is disabled for the remainder of the current driving cycle and the EGR Monitor will be set to a "ready" condition.

A DTC of P1408, like the P0400, will indicate a EGR flow failure (outside the minimum or maximum limits) but is only set during the KOER self test. The P0400 and P0403 are MIL codes. P1408 is a non-MIL code.

Scheme 206

Fuel System Monitor

The 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 the PCM's Keep Alive Memory (KAM) to compensate for variability in fuel system components due to normal wear and aging. Fuel trim tables are based on engine rpm and engine load. During closed-loop fuel control, the fuel trim strategy learns the corrections needed to correct a "biased" rich or lean fuel system. The correction is stored in the fuel trim tables. The fuel trim has two means of adapting; Long Term Fuel Trim and a Short Term Fuel Trim. Both are described in greater detail under Powertrain Control Software, Fuel Trim. Long Term relies on the fuel trim tables and Short Term refers to the desired air/fuel ratio parameter called "LAMBSE". LAMBSE is calculated by the PCM from HO2S inputs and helps maintain a 14.7:1 air/fuel ratio during closed-loop operation. Short Term Fuel Trim and Long Term Fuel Trim work together. If the HO2S indicates the engine is running rich, the PCM will correct the rich condition by moving Short Term Fuel Trim in the negative range (less fuel to correct for a rich combustion). If after a certain amount of time the Short Term Fuel Trim is still compensating for a rich condition, the PCM "learns" this and moves the Long Term Fuel Trim into the negative range to compensate and allows Short Term Fuel Trim to return to a value near 0%. Input from the ECT or CHT, IAT, and MAF sensors is required to activate the fuel trim system, which in turn activates the Fuel System Monitor. Once activated, the Fuel System Monitor looks for the fuel trim tables to reach the adaptive clip (adaptive limit) and LAMBSE to exceed a calibrated limit. The Fuel System Monitor will store the appropriate DTC when a fault is detected as described below.

1. The heated oxygen sensor (HO2S) detects the presence of oxygen in the exhaust and provides the PCM with feedback indicating air/fuel ratio.
2. A correction factor is added to the fuel injector pulsewidth calculation and/or mass air flow calculation, according to the Long and Short Term Fuel Trims as needed to compensate for variations in the 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: The DTCs associated with the monitor detecting a lean shift in fuel system operation are DTCs P0171 (Bank 1) and P0174 (Bank 2). The DTCs associated with the monitor detecting a rich shift in fuel system operation are DTCs P0172 (Bank 1) and P0175 (Bank 2).
4. The MIL is activated after a fault is detected on two consecutive drive cycles.

Typical Fuel System Monitor Entry Conditions

1. RPM range between at Idle.
2. Air Mass Range greater than 0.75 lb/min.
3. Purge duty cycle of 0%.

Typical Fuel Monitor Malfunction Thresholds

1. Lean Malfunction: LONGFT > 25%, SHRTFT > 5%.
2. Rich Malfunction: LONGFT < 25%, SHRTFT < 10%

Scheme 207

Heated Oxygen Sensor (HO2S) Monitor

The HO2S Monitor is an on-board strategy designed to monitor the HO2S sensors for a malfunction or deterioration which can affect emissions. The fuel control or Stream 1 HO2S sensors are checked for proper output voltage and response rate (the time it takes to switch from lean to rich or rich to lean). Stream 2 HO2S sensors used for Catalyst Monitoring, and Stream 3 HO2S sensors used for FAOS (Fore-Aft Oxygen Sensor) control are also monitored for proper output voltage. Input is required from the ECT or CHT, IAT, MAF and CKP sensors to activate the HO2S Monitor. The Fuel System Monitor and Misfire Detection Monitor must also have completed successfully before the HO2S Monitor is enabled.

1. The HO2S sensor senses the oxygen content in the exhaust flow and outputs a voltage between zero and 1.0 volt. Lean of stoichiometric (air/fuel ratio of approximately 14.7:1), the HO2S will generate a voltage between zero and 0.45 volt. Rich of stoichiometric, the HO2S will generate a voltage between 0.45 and 1.0 volt. The HO2S Monitor evaluates the Stream 1 (Fuel Control) and Stream 2 (Catalyst Monitor) and the Stream 3 (FAOS Control) HO2Ss for proper function.
2. The time between HO2S switches is monitored after vehicle startup and during closed loop fuel conditions. Excessive time between switches or no switches since startup indicates a malfunction. Since lack of switching malfunctions can be caused by HO2S sensor malfunctions or by shifts in the fuel system, DTCs are stored that provide additional information for the lack of switching malfunction. Different DTCs indicate whether the sensor was always indicates lean/disconnected (P1131 or P2195, P1151 or P2197), or always indicates rich (P1132 or P2196, P1152 or P2198). 2004 MY vehicles will monitor the HO2S signal for high voltage, in excess of 1.1 volts and store a unique DTC. (P0132, P0152). An over voltage condition is caused by a HO2S heater or battery power short to the HO2S signal line. A functional test of the rear HO2S sensors is done during normal vehicle operation. The peak rich and lean voltages are continuously monitored. Voltages that exceed the calibratable rich and lean thresholds indicate a functional sensor. If the voltages have not exceeded the thresholds after a long period of vehicle operation, the air/fuel ratio may be forced rich or lean in an attempt to get the rear sensor to switch. This situation normally occurs only with a green catalyst (< 500 miles). If the sensor does not exceed the rich and lean peak thresholds, a malfunction is indicated. 2004 MY vehicles will monitor the rear HO2S signal for high voltage, in excess of 1.1 volts and store a unique DTC. (P0138, P0158). An over voltage condition is caused by a HO2S heater or battery power short to the HO2S signal line.
3. The MIL is activated after a fault is detected on two consecutive drive cycles.
4. Some 2004 Partial Zero Emission Vehicles (PZEV Focus) will utilize three sets of HO2S sensors. The front sensors (HO2S11/HO2S21) are the primary fuel control sensors. The next sensors downstream in the exhaust are utilized to monitor the light-off catalyst (HO2S12/HO2S22). The last sensors downstream in the exhaust (HO2S13/HO2S23) are utilized for very long term fuel trim in order to optimize catalyst efficiency (Fore Aft Oxygen Sensor Control). Ford's first PZEV vehicle uses a 4-cylinder engine so only the Bank 1 DTCs are utilized.

The HO2S Monitor DTCs can be categorized as follows

1. HO2S signal circuit malfunction - P0131, P0136, P0151, P0156.
2. HO2S slow response rate - P0133, P0153.
3. HO2S circuit high voltage - P0132, P0138, P0144, P0152, P0158, P0164.
4. HO2S heater circuit malfunction - P0135, P0141, P0155, P0161, P0147, P0167.
5. HO2S heater current malfunction - P0053, P0054, P0055, P0059, P0060, P0061.
6. Downstream HO2S not running in on-demand self test - P1127.
7. Swapped HO2S connectors - P0040, P0041, P1128, P1129, P2278.
8. HO2S lack of switching - P1131, P1132, P1151, P1152, P2195, P2196, P2197, P2198.
9. HO2S lack of switching (Sensor indicates lean) - P1137, P1157, P2270, P2272, P2274, P2276.
10. HO2S lack of switching (Sensor indicates rich) - P1138, P1158, P2271, P2273, P2275, P2277.

Scheme 208

Scheme 209

Misfire Detection Monitor

The Misfire Detection Monitor is an on-board strategy designed to monitor engine misfire and identify the specific cylinder in which the 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. The Misfire Detection Monitor will be enabled only when certain base engine conditions are first satisfied. Input from the ECT or CHT, MAF and CKP sensors is required to enable the monitor. The Misfire Detection Monitor is also performed during on demand self-test.

1. The PCM synchronized ignition spark is based on information received from the CKP sensor. The CKP signal generated is also the main input used in determining cylinder misfire.
2. The input signal generated by the CKP sensor is derived by sensing the passage of teeth from the crankshaft position wheel mounted on the end of the crankshaft.
3. The input signal to the PCM is then used to calculate the time between CKP edges and also crankshaft rotational velocity and acceleration. By comparing the accelerations of each cylinder event, the power loss of each cylinder is determined. When the power loss of a particular cylinder is sufficiently less than a calibrated value and other criteria is met, then the suspect cylinder is determined to have misfired.

Scheme 210

Low Data Rate System

The LDR Misfire Monitor uses a low-data -rate crankshaft position signal, (i.e. one position reference signal at 10 deg BTDC for each cylinder event). The PCM calculates crankshaft rotational velocity for each cylinder from this crankshaft position signal. The acceleration for each cylinder can then be calculated using successive velocity values. The changes in overall engine rpm are removed by subtracting the median engine acceleration over a complete engine cycle. The resulting deviant cylinder acceleration values are used in evaluating misfire in the GENERIC MISFIRE PROCESSING .

High Data Rate System

The HDR Misfire Monitor uses a high data rate crankshaft position signal, (i.e. 18 position references per crankshaft revolution [20 on a V-10]). This high-resolution signal is processed using two different algorithms. The first algorithm, called pattern cancellation, is optimized to detect low rates of misfire. The algorithm learns the normal pattern of cylinder accelerations from the mostly good firing events and is then able to accurately detect deviations from that pattern. The second algorithm is optimized to detect hard misfires, i.e. one or more continuously misfiring cylinders. This algorithm filters the high-resolution crankshaft velocity signal to remove some of the crankshaft torsional vibrations that degrade signal to noise. This significantly improves detection capability for continuous misfires. Both algorithms produce a deviant cylinder acceleration value, which is used in evaluating misfire in the Generic Misfire Processing. Due to the high data processing requirements, the HDR algorithms could not be implemented in the PCM microprocessor. They are implemented in a separate chip in the PCM called an AICE chip. The PCM microprocessor communicates with the AICE chip using a dedicated serial communication link. The output of the AICE chip (the cylinder acceleration values) is sent to the PCM microprocessor for additional processing as described below. Lack of serial communication between the AICE chip and the PCM microprocessor, or an inability to synchronize the crank or cam sensors inputs sets a P1309 DTC. For 2004 MY software, the P1309 DTC is being split into two separate DTCs. A P0606 will be set if there is a lack of serial communication between the AICE chip and the PCM microprocessor. A P1336 will be set if there is an inability to synchronize the crank or cam sensors inputs. This change was made to improve serviceability. A P0606 generally results in PCM replacement while a P1336 points to a cam sensor that is out of synchronization with the crank. Profile correction software is used to learn and correct for mechanical inaccuracies in crankshaft tooth spacing under de-fueled engine conditions (requires three 60 to 40 mph no-braking decels after Keep Alive Memory has been reset). If KAM has been reset, the PCM microprocessor initiates a special routine which computes correction factors for each of the 18 (or 20) position references and sends these correction factors back to the AICE chip to be used for subsequent misfire signal processing. These learned corrections improve the high rpm capability of the monitor. The misfire monitor is not active until a profile has been learned.

Generic Misfire Processing

The acceleration that a piston undergoes during a normal firing event is directly related to the amount of torque that cylinder produces. The calculated piston/cylinder acceleration value(s) are compared to a misfire threshold that is continuously adjusted based on inferred engine torque. Deviant accelerations exceeding the threshold are conditionally labeled as misfires. The calculated deviant acceleration value(s) are also evaluated for noise. Normally, misfire results in a nonsymmetrical loss of cylinder acceleration. Mechanical noise, such as rough roads or high rpm/light load conditions, will produce symmetrical acceleration variations. Cylinder events that indicate excessive deviant accelerations of this type are considered noise. Noise-free deviant acceleration exceeding a given threshold is labeled a misfire. The number of misfires are counted over a continuous 200 revolution and 1000 revolution period. (The revolution counters are not reset if the misfire monitor is temporarily disabled such as for negative torque mode, etc.) At the end of the evaluation period, the total misfire rate and the misfire rate for each individual cylinder is computed. The misfire rate evaluated every 200 revolution period (Type A) and compared to a threshold value obtained from an engine speed/load table. This misfire threshold is designed to prevent damage to the catalyst due to sustained excessive temperature (1600°F for Pt/Pd/Rh conventional washcoat, 1650°F for Pt/Pd/Rh advanced washcoat and 1800°F for Pd-only high tech washcoat). If the misfire threshold is exceeded and the catalyst temperature model calculates a catalyst mid-bed temperature that exceeds the catalyst damage threshold, the MIL blinks at a 1 Hz rate while the misfire is present. If the threshold is again exceeded on a subsequent driving cycle, the MIL is illuminated. If a single cylinder is indicated to be consistently misfiring in excess of the catalyst damage criteria, the fuel injector to that cylinder may be shut off for a period of time to prevent catalyst damage. Up to two cylinders may be disabled at the same time. This fuel shut-off feature is used on many 8 -cylinder engine and some 6- cylinder engines. It is never used on a 4 -cylinder engine. Next, the misfire rate is evaluated every 1000 rev period and compared to a single (Type B) threshold value to indicate an emission-threshold malfunction, which can be either a single 1000 rev exceedence from startup or four subsequent 1000 rev exceedences on a drive cycle after start-up. Many 2004 MY vehicles will set a P0316 DTC if the Type B malfunction threshold is exceeded during the first 1,000 revs after engine startup. This DTC is stored in addition to the normal P03xx DTC that indicates the misfiring cylinder(s).

Profile Correction

"Profile correction" software is used to "learn" and correct for mechanical inaccuracies in the crankshaft position wheel tooth spacing. Since the sum of all the angles between crankshaft teeth must equal 360°, a correction factor can be calculated for each misfire sample interval that makes all the angles between individual teeth equal. To prevent any fueling or combustion differences from affecting the correction factors, learning is done during decel fuel cutout. The correction factors are learned during closed-throttle, non-braking, de-fueled decelerations in the 60 to 40 mph range after exceeding 60 mph (likely to correspond to a freeway exit condition). In order to minimize the learning time for the correction factors, a more aggressive decel-fuel cutout strategy may be employed when the conditions for learning are present. The corrections are typically learned in a single deceleration, but can be learned during up to 3 such decelerations. The "mature" correction factors are the average of a selected number of samples. A low data rate misfire system will typically learn 4 such corrections in this interval, while a high data rate system will learn 36 or 40 in the same interval (data is actually processed in the AICE chip). In order to assure the accuracy of these corrections, a tolerance is placed on the incoming values such that an individual correction factor must be repeatable within the tolerance during learning This is to reduce the possibility of learning corrections on rough road conditions which could limit misfire detection capability. Since inaccuracies in the wheel tooth spacing can produce a false indication of misfire, the misfire monitor is not active until the corrections are learned. In the event of battery disconnection or loss of Keep Alive Memory the correction factors are lost and must be relearned. If the software is unable to learn a profile after three 60 to 40 mph decels, a P0315 DTC is set.

PCV System Monitor

The PCV Monitor consists of a modified PCV system design. The PCV valve is installed into the rocker cover using a quarter-turn cam-lock design to prevent accidental disconnection. High retention force molded plastic lines are used from the PCV valve to the intake manifold. The diameter of the lines and the intake manifold entry fitting are increased so that inadvertent disconnection of the lines after a vehicle is serviced will cause either an immediate engine stall or will not allow the engine to be restarted. In the event that the vehicle does not stall if the line between the intake manifold and PCV valve is inadvertently disconnected, the vehicle will have a large vacuum leak that will cause the vehicle to run lean at idle. This will illuminate the MIL after two consecutive driving cycles and will store one or more of the following DTCs: Lack of O2 sensor switches, Bank 1 (P1131 or P2195), Lack of O2 sensor switches Bank 2 (P1151 or P2197), Fuel system Lean, Bank 1 (P0171) or Fuel System Lean, Bank 2 (P0174).

For additional PCV information refer to POSITIVE CRANKCASE VENTILATION SYSTEM .

Secondary Air Injection (AIR) System Monitor-Electric Secondary Air Injection Pump System

The Secondary Air Injection (AIR) System Monitor is an on-board strategy designed to monitor the proper function of the secondary air injection system. The AIR Monitor for the Electric Secondary Air Injection Pump system consists of two monitor circuits: an AIR circuit to diagnose concerns with the primary circuit side of the AIR relay, and an AIR Monitor circuit to diagnose concerns with the secondary circuit side of the AIR relay. A functional check is also performed that tests the ability of the AIR system to inject air into the exhaust. The functional check relies upon HO2S sensor feedback to determine the 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 the CHT, IAT, and CKP sensors and the HO2S Monitor test must also have passed without a fault detection to enable the AIR Monitor. The AIR Monitor is also activated during on demand self-test.

1. On the primary side of the AIR relay, open and short circuit faults are detected during normal operation by the PCM output driver. The DTC associated with this test is DTC P0412.
2. On the secondary side of the AIR relay, the AIR Monitor circuit is held low by the resistance path through the AIR pump when the pump is off. If the AIR Monitor circuit is high there is either an open circuit to the PCM from the pump or there is power supplied to the AIR Pump. If the AIR Monitor is low when the pump is commanded on, there is either an open circuit from the AIR relay or the AIR relay has failed to supply power to the pump. The DTCs associated with this test are DTCs P2257 and P2258.
3. The functional check may be done in two parts: at startup when the AIR pump is normally commanded on, or during a hot idle if the startup test was not able to be performed. The flow test relies upon the HO2S to detect the presence of additional air in the exhaust when introduced by the Secondary Air Injection system. The DTC associated with this test is DTC P0411.
4. The MIL is activated after one of the above tests fail on two consecutive drive cycles.

Scheme 211

Thermostat Monitor

The Thermostat Monitor is designed to verify proper thermostat operation. This monitor will be executed once per drive cycle and has a monitor run duration of 300-800 seconds. If a malfunction occurs, a diagnostic trouble code P0125 or P0128 will be set and the malfunction indicator lamp will be illuminated.

The monitor checks the engine coolant temperature (ECT) or cylinder head temperature (CHT) sensor to warm up in a predictable manner when the engine is generating sufficient heat. A timer is incremented while the engine is at moderate load and the vehicle speed is above a calibrated limit. The target timer value is based on ambient air temperature at start-up. If the timer exceeds the target time and ECT/CHT has not warmed up to the target temperature, a malfunction is indicated. The test runs if the start-up intake air temperature from the IAT sensor is at, or below the target temperature. A two-hour engine off soak time is also required to enable the monitor and to prevent erasing of any pending DTC during a hot soak. This soak time feature will also prevents false-passes of the monitor when the engine coolant temperature rises after the engine is turned off during a short engine off soak period.

The target temperature will be calibrated to the thermostat regulating temperature minus 20°F (11°C). For a typical 195°F (90°C) thermostat, the warm-up temperature would be calibrated to 175°F (79°C). For the 2004 model year, some vehicle calibrations may lower the target temperature below 50 °F (10 °C) for vehicles that do not warm -up to thermostat regulating temperatures in the 20°F (-7 °C) to 50 °F (10 °C) ambient temperature range.

1. Inputs: ECT or CHT, IAT, engine LOAD (from MAF sensor) and vehicle speed input. Typical Monitor entry conditions: Vehicle speed greater than 15 mph (24 km/h) Intake Air temperature at start -up is between 20 °F (-7 °C) and target thermostat temperature Engine load greater than 30% Engine off (soak) time greater than a 2 hours
2. Output: MIL.

Scheme 212

Malfunction Indicator Lamp (MIL)

The malfunction indicator lamp (MIL) (Scheme 213) alerts the driver that the powertrain control module (PCM) has detected an OBD II emission-related component or system fault. When this occurs, an OBD II Diagnostic Trouble Code (DTC) will be set.

1. The MIL is located on the instrument cluster and is labeled CHECK ENGINE, SERVICE ENGINE SOON or ISO standard engine symbol (Scheme 214)
2. Power is supplied to the MIL whenever the ignition switch is in the RUN or START position.
3. The MIL will remain on in the RUN/START mode as a bulb check during the instrument cluster proveout for approximately 4 seconds.
4. If the MIL remains on after the bulb check: The PCM illuminates the MIL for an emission related concern and a DTC will be present. The instrument cluster will illuminate the MIL if the PCM does not send a control message to the instrument cluster. The PCM is operating in the Hardware Limited Operation Strategy (HLOS). The MIL circuit is shorted to ground.
5. If the MIL remains off (during the bulb check): Bulb is damaged. MIL circuit is open.
6. To turn off the MIL after a repair, a reset command from the Scan Tool must be sent, or three consecutive drive cycles must be completed without a fault.
7. For any MIL concern, go to «SYMPTOM CHARTS - CNG, FLEX-FUEL & GASOLINE»(ref-227201).
8. If the MIL blinks at a steady rate, a severe misfire condition could possibly exist.
9. If the MIL blinks erratically, an intermittent open B+ to the bulb or an intermittent short to ground in the MIL circuit exist. Also, the PCM can reset while cranking if battery voltage is low.

Scheme 213

Scheme 214

Modifications to OBD Vehicles

Modifications or additions to the vehicle may cause incorrect operation of the OBD system. Anti-theft systems, cellular telephones and CB radios must be carefully installed. Do not install these devices by tapping into or running wires close to powertrain control system wires or components .

Multiplexing

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

Multiplexing Implementation

Currently Ford Motor Company uses two different types of communication language protocols to communicate with the powertrain control module (PCM). These protocols are Standard Corporate Protocol (SCP) and Controller Area Network (CAN). For the 2004 model year the following vehicles will utilize the High Speed -CAN (HS-CAN) protocol for PCM communication

1. 2.3L Focus PZEV (partial zero emission vehicle)
2. LS6
3. LS8
4. Taurus/Sable
5. Thunderbird
6. Explorer/Mountaineer
7. 4.6L 2V and 5.4L 3V F150 (Non-Heritage)

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

All other vehicles for model year 2004 will continue to use SCP as its communication media for the PCM. For more information about the entire communication network refer to the appropriate MODULE COMMUNICATION NETWORK .

Standard Corporate Protocol (SCP)

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

Included in these messages is diagnostic data that is outputted over the BUS (+) and BUS (-) lines to the data link connector (DLC). PCM connection to the DLC is typically done with a two wire, twisted pair cable used for network interconnection. The diagnostic data such as Self-test or PIDs can be accessed with a scan tool. Information on scan tool equipment is described in DIAGNOSTIC METHODS - CNG, FLEX-FUEL & GASOLINE .

High Speed - Controller Area Network (HS-CAN)

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

Included in these messages is diagnostic data that is outputted over the CAN High (+) and CAN Low (-) lines to the data link connector (DLC). PCM connection to the DLC is typically done with a two wire, twisted pair cable used for the network interconnection. The diagnostic data such as Self-test or PIDs can be accessed with a scan tool. Information on scan tool equipment is described in DIAGNOSTIC METHODS - CNG, FLEX-FUEL & GASOLINE .

Flash Electrically Erasable Programmable Read Only Memory

The Flash Electrically Erasable Programmable Read Only Memory (EEPROM) is an Integrated Circuit (IC) within the PCM. This IC contains the software code required by the PCM to control the powertrain. One feature of the EEPROM is that it can be electrically erased and then reprogrammed without removing the PCM from the vehicle. If a software change is required to the PCM, the module no longer needs to be replaced, but can be reprogrammed at the dealership through the DLC.

Idle Air Trim

Idle air trim is designed to adjust the idle air control (IAC) calibration to correct for wear and aging of components. When the engine conditions meet the learning requirement, the strategy monitors the engine and determines the values required for ideal idle calibration. The idle air trim values are stored in a table for reference. This table is used by the PCM as a correction factor when controlling the idle speed. The table is stored in keep alive memory (KAM) and retains the learned values even after the engine is shut off. A diagnostic trouble code (DTC) is output if the idle air trim has reached its learning limits.

Whenever an IAC component is repaired or cleaned, or a repair affecting idle is carried out, it is recommended that the KAM be reset. This is necessary so the idle strategy does not use the previously learned idle air trim values.

To reset the KAM, refer to RESETTING THE KEEP ALIVE MEMORY (KAM) . It is important to note that erasing DTCs with a diagnostic tool does not reset the idle air trim table.

Once the KAM has been reset, the engine must idle for 15 minutes (actual time varies between strategies) to learn new idle air trim values. Idle quality will improve as the strategy adapts. Adaptation occurs in 4 separate modes. The modes are shown in the following table.

IDLE AIR TRIM LEARNING MODES

Short Term Fuel Trim

If the oxygen sensors are warmed up and the PCM determines that the engine can operate near stoichiometric air/fuel ratio (14.7 to 1 for gasoline), the PCM goes into closed loop fuel control mode. Since an oxygen sensor can only indicate rich or lean, the fuel control strategy must constantly adjust the desired air/fuel ratio rich and lean to get the oxygen sensor to "switch"around the stoichiometric point. If the time between switches are the same, then the system is actually operating at stoichiometry. The desired air/fuel control parameter is called short term fuel trim (SHRTFT1 and 2) where stoichiometry is represented by 0%. Richer (more fuel) is represented by a positive number and leaner (less fuel) is represented by a negative number. Normal operating range for short term fuel trim is +/- 25%. Some calibrations will have time between switches and short term fuel trim excursions that are not equal. These unequal excursions are used to run the system slightly lean or rich of stoichiometry. This practice is referred to as using "bias". For example, the fuel system can be biased slightly rich during closed loop fuel to help reduce NOx.

Values for SHRTFT1 and 2 may change a great deal on a scan tool when the engine is operated at different rpm and load points. This is because SHRTFT1 and 2 will react to fuel delivery variability that can change as a function of engine rpm and load. Short term fuel trim values are not retained after the engine is turned off.

Long Term Fuel Trim

While the engine is operating in closed loop fuel, the short term fuel trim corrections can be "learned" by the PCM as long term fuel trim (LONGFT1 and 2) corrections. These corrections are stored in Keep Alive Memory (KAM) in tables that are referenced by engine speed and load (and by bank for engines with two HO2S sensors forward of the catalyst). Learning the corrections in KAM improves both open loop and closed loop air/fuel ratio control. Advantages include

1. Short term fuel trim does not have to generate new corrections each time the engine goes into closed loop.
2. Long term fuel trim corrections can be used both while in open loop and closed loop modes.

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

Failure Mode Effects Management

Failure Mode Effects Management (FMEM) is an alternate system strategy in the 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 the PCM, an alternative strategy is initiated. The PCM substitutes a fixed value and continues to monitor the incorrect sensor input. If the suspect sensor operates within limits, the PCM returns to the normal engine operational strategy.

All FMEM sensors display a sequence error message on the scan tool. The message may or may not be followed by Key On Engine Off or Continuous Memory DTCs when attempting Key On Engine Running Self-Test Mode.

Engine RPM/Vehicle Speed Limiter

The powertrain control module (PCM) will disable some or all of the fuel injectors whenever an engine rpm or vehicle overspeed condition is detected. The purpose of the engine rpm or vehicle speed limiter is to prevent damage to the powertrain. The vehicle will exhibit a rough running engine condition, and the PCM will store one of the following Continuous Memory DTCs: P0219, P0297 or P1270. Once the driver reduces the excessive speed, the engine will return to the normal operating mode. No repair is required. However, the technician should clear the PCM and inform the customer of the reason for the 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.

Powertrain Control Module

The center of the Electronic EC system is a microprocessor called the powertrain control module (PCM). The PCM receives input from sensors and other electronic components (switches, relays). Based on information received and programmed into its memory, the PCM generates output signals to control various relays, solenoids and actuators. There are several different types of PCM's in use for this model year. Refer to the vehicle PCM application table below for PCM type and their applications.

VEHICLE PCM APPLICATION

Natural Gas (NG) Vehicle Module

The natural gas (NG) vehicle module (Scheme 215) provides two functions. The first function operates the fuel injectors and is referred to as the injector driver module (IDM). The second function sends a fuel level indicator signal to drive the fuel gauge and is called the fuel indicator module (FIM). IDM NG vehicle fuel indicator driver signals are based on powertrain control module (PCM) fuel injector driver signals and are controlled directly by the corresponding injector drivers in the PCM. The IDM must be used to provide the NG fuel injectors with the required high current necessary for proper operation. The greater demand of NG fuel injector current warrants an increased size of the injector driver and increased heat dissipation. Given these conditions, the PCM would not be suitable for placement of these drivers. The IDM closely resembles the Electronic Engine Control 60 Pin PCM module in appearance. This style of module is used on the NG F-Series and Crown Victoria, while a 90 pin Alternative Fuel Control Module (AFCM) (Scheme 216) is used on the E-Series.

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

The fuel indicator module (FIM) is not part of the powertrain control subsystem and will not be discussed here.

Scheme 215

Scheme 216

Constant Control Relay Module

The constant control relay module (CCRM) interfaces with the Electronic EC system to provide vehicle power (VPWR) to the powertrain control module (PCM) and the Electronic EC system, and for the control of the cooling fan and A/C clutch. The CCRM also contains the fuel pump driver module (FPDM) power supply relay, which supplies power to the FPDM. If any of the internal components of the CCRM fail, the entire unit must be replaced. The descriptions of the specific CCRM functions, as well as the Dual Function A/C high pressure switch are found under the individual hardware - PCM inputs and outputs in this article.

Fuel Pump Driver Module

Note. For the Thunderbird and LS6/LS8, the FPDM functions are incorporated in the Rear Electronic Module (REM). Fuel pump operation is the same as applications using the stand-alone FPDM. The REM will, however, communicate diagnostic information through the communication link instead of using a fuel pump monitor (FPM) circuit.

The fuel pump driver module (FPDM) receives a duty cycle signal from the PCM and controls the fuel pump operation in relation to this duty cycle. This results in variable speed fuel pump operation. The FPDM sends diagnostic information to the PCM on the fuel pump monitor circuit. For additional information, refer to PCM OUTPUTS , FUEL PUMP and PCM INPUTS , FUEL PUMP MONITOR .

Generic Electronic Module

For information on the generic electronic module, refer to the description of the Transfer Case 4x4 System in the appropriate MULTIFUNCTION ELECTRONIC MODULE article.

Keep Alive Memory (KAM)

The PCM stores information in KAM (a memory integrated circuit chip) about vehicle operating conditions and then uses this information to compensate for component variability. KAM remains powered when the ignition switch is off so that this information is not lost.

Integrated Electronic Ignition System

The Integrated Electronic Ignition (EI) System consists of a crankshaft position (CKP) sensor, coil pack(s), connecting wiring, and PCM. The Coil On Plug (COP) Integrated EI System uses a separate coil for each spark plug and each coil is mounted directly onto the plug. The COP Integrated EI System eliminates the need for spark plug wires but does require input from the camshaft position (CMP) sensor.

Vehicle Buffered Power (VBPWR)

Vehicle Buffered Power (VBPWR) is a PCM supplied power source that supplies regulated voltage (10 to 14 volts) to vehicle sensors that run off 12 volts but cannot withstand VPWR voltage variations. It is regulated to VPWR minus 1.5 volts and is voltage limited to protect the sensors.

Vehicle Power (VPWR)

When the ignition switch is turned to the START or RUN position, battery positive voltage (B+) is applied to the coil of the Electronic EC power relay. Since the other end of the coil is wired to ground, this energizes the coil and closes the contacts of the Electronic EC power relay. Vehicle power (VPWR) is now sent to the PCM and the Electronic EC System as VPWR.

Vehicle Reference Voltage (VREF)

The vehicle reference voltage (VREF) is a positive voltage (about 5.0 volts) that is output by the PCM. This is a consistent voltage that is used typically by the 3-wire sensors and some digital input signals.

Mass Air Flow Return

The mass air flow return (MAF RTN) is a dedicated analog signal return from the mass air flow (MAF) sensor. It serves as a ground offset for the analog voltage differential input by the MAF sensor to the PCM.

Signal Return

The signal return (SIG RTN) is a dedicated ground circuit used by most Electronic EC sensors and some other inputs.

Power Ground

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

Gold Plated Pins

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

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

PCM Inputs

Note. Transmission input, which are not described in this article are discussed in the respective AUTOMATIC TRANSMISSION article.

Air Conditioning Cycling Switch

The air conditioning (A/C) cycling switch may be wired to either the ACCS or ACPSW PCM input. When the A/C cycling switch opens, the PCM will turn off the A/C clutch. For information on the specific function of the A/C cycling switch, refer to the appropriate CLIMATE CONTROL SYSTEM article.

The A/C cycling switch (ACCS) circuit to the PCM provides a voltage signal which indicates when the A/C is requested. When the A/C demand switch is turned on, and both the A/C cycling switch and the high pressure contacts of the A/C high pressure switch (if equipped and in circuit) are closed, voltage is supplied to the ACCS circuit at the PCM. Refer to the appropriate SYSTEM WIRING DIAGRAMS article for vehicle specific wiring.

If the ACCS signal is not received by the PCM, the PCM circuit will not allow the A/C to operate. For additional information, refer to PCM OUTPUTS , wide open throttle air conditioning cutoff.

Note. Some applications do not have a dedicated (separate) input to the PCM indicating that A/C is requested. This information is received by the PCM through the communication link.

Air Conditioning Evaporator Temperature Sensor

The air conditioning evaporative temperature (ACET) sensor senses evaporator air discharge temperature. The ACET sensor is a thermistor device in which resistance changes with temperature. The electrical resistance of a thermistor decreases as the temperature increases, and increases as the temperature decreases. The PCM sources a low current 5 volts on the ACET circuit. With SIG RTN also connected to the ACET sensor, the varying resistance affects the voltage drop across the sensor terminals. As A/C evaporator air temperature changes, the varying resistance of the ACET sensor changes the voltage the PCM detects.

The ACET sensor is used to more accurately control A/C clutch cycling, improving defrost/demist performance, reduce A/C clutch cycling, etc.

A/C EVAPORATOR TEMPERATURE (ACET) SENSOR VOLTAGE AND RESISTANCE

Note. These values can vary 15 percent due to sensor and VREF variations. Voltage values were calculated for VREF = 5.0 volts.

Air Conditioning Pressure Sensor

The air conditioning pressure (A/C pressure) sensor (Scheme 218) is located in the high pressure (discharge) side of the air conditioning A/C system. The A/C pressure sensor provides a voltage signal to the powertrain control module (PCM) that is proportional to the A/C pressure. The PCM uses this information for A/C clutch control, fan control and idle speed control.

Scheme 217

Scheme 218

Air Conditioning High Pressure Switch

The A/C high pressure switch is used for additional A/C system pressure control. The A/C high pressure switch is either dual function for two-speed electric fan applications or single function for all others.

For refrigerant containment control, the normally closed high pressure contacts open at a predetermined A/C pressure. This will result in the A/C turning off, preventing the A/C pressure from rising to a level that would open the 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 the PCM. The PCM will then turn on the high speed fan to help reduce the pressure.

For additional information, refer to the appropriate CLIMATE CONTROL SYSTEM article or the appropriate SYSTEM WIRING DIAGRAMS article.

Brake Pedal Position Switch

The brake pedal position (BPP) switch (Scheme 219) is used by the PCM to disengage the transmission torque converter clutch and on some applications as an input to the idle speed control for idle quality and for vehicle speed control deactivation. Depending on the vehicle application the BPP switch can be connected to the PCM in the following manner

1. BPP switch is hard wired to the PCM supplying battery positive voltage (B+) when the vehicle brake is applied.
2. BPP switch is hard wired to a module (ABS, LCM or REM), BPP signal is than broadcasted over the data link to be received by the PCM.
3. BPP switch is hard wired to the anti-lock brake (ABS)- traction control / stability assist module. The stability module will interpret the BPP switch input along with other ABS inputs and generate an output called the Driver Brake Application (DBA) signal. The DBA signal is than sent to the PCM and to other BPP signal users.

Note on applications where the BPP switch is hard wired to the PCM and stoplamp circuit, if all stoplamp bulbs are burned out (open), high voltage is present at the PCM due to a pull-up resistor in the PCM. This provides fail-safe operation in the event the circuit to the stoplamp bulbs has failed.

Scheme 219

Brake Pressure Applied/Brake Deactivator Switch

The brake pressure applied (BPA) switch also sometimes called the brake deactivator switch for vehicle speed control deactivation. Is a normally closed switch, witch supplies battery positive voltage (B+) to the PCM when the brake pedal is NOT applied. When the brake pedal is depressed, the normally closed switch will open and power is removed from the 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 the PCM. The PCM misfire monitor profile learn function can be disable if a brake switch failure occurs. If one or both brake pedal inputs to the PCM did not change states when they were expected to a diagnostic trouble code P1572 can be set by the PCM strategy.

Camshaft Position Sensor

The camshaft position (CMP) sensor detects the position of the camshaft. The CMP sensor identifies when piston No. 1 is on its compression stroke. A signal is then sent to the powertrain control module (PCM) and used for synchronizing the sequential firing of the fuel injectors. The Coil On Plug (COP) ignition applications also use the CMP signal to select the proper ignition coil to fire. The input circuit to the PCM is referred to as the CMP input or circuit. DTC P0340 is associated with this sensor.

Vehicles with two CMP sensors are equipped with variable camshaft timing (VCT). They use the second sensor to identify the position of the camshaft on bank 2 as an input to the PCM. DTC P0345 is associated with this sensor and it is referred to as CMP2.

There are two types of CMP sensors: the three pin connector Hall-effect type sensor (Scheme 220) found on F-Series 4.2L applications, and the two pin connector variable reluctance sensor found on all other vehicles(Scheme 221)

Scheme 220

Scheme 221

Clutch Pedal Position Switch

The clutch pedal position (CPP) switch (Scheme 222) is an input to the PCM indicating the clutch pedal position. The PCM provides a 5-volt reference (VREF) signal to the CPP switch. If the CPP switch is closed, indicating the clutch pedal is engaged, the output voltage (5 volts) from the PCM is grounded through the signal return line to the PCM, and there is 1 volt or less. One volt or less indicates there is a reduced load on the engine. If the CPP switch is open, meaning the clutch pedal is disengaged, the input on the CPP signal to the PCM will be approximately 5 volts. Then, the 5-volt signal input at the PCM will indicate a load on the engine. The PCM uses the load information in mass air flow and fuel calculations.

Scheme 222

Crankshaft Position Sensor (Integrated Ignition Systems)

The crankshaft position (CKP) sensor is a magnetic transducer mounted on the engine block or timing cover and is adjacent to a pulse wheel located on the crankshaft. By monitoring the crankshaft mounted pulse wheel, the CKP is the primary sensor for ignition information to the powertrain control module (PCM). The trigger wheel has a total of 35 teeth spaced 10 degrees apart with one empty space for a missing tooth. The 6.8L ten cylinder pulse wheel has 39 teeth spaced 9 degrees apart and one 9 degree empty space for a missing tooth. By monitoring the trigger wheel, the CKP indicates crankshaft position and speed information to the PCM. By monitoring the missing tooth, the CKP is also able to identify piston travel in order to synchronize the ignition system and provide a way of tracking the angular position of the crankshaft relative to fixed reference (Scheme 223)

Scheme 223

Cylinder Head Temperature Sensor

The cylinder head temperature (CHT) sensor (Scheme 224) is a thermistor device in which resistance changes with temperature. The electrical resistance of a thermistor decreases as temperature increases, and increases as temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature.

Thermistor-type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying the resistance of the passive sensor causes a variation in total current flow.

Voltage that is dropped across a fixed resistor in series with the sensor resistor determines the voltage signal at the PCM. This voltage signal is equal to the reference voltage minus the voltage drop across the fixed resistor.

The cylinder head temperature (CHT) sensor is installed in the aluminum cylinder head and measures the metal temperature. The CHT sensor can provide complete engine temperature information and can be used to infer coolant temperature. If the CHT sensor conveys an overheating condition to the PCM, the PCM would then initiate a fail-safe cooling strategy based on information from the CHT sensor. 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. Using both the CHT sensor and fail-safe cooling strategy, the PCM prevents damage by allowing air cooling of the engine and limp home capability. For additional information, refer to POWERTRAIN CONTROL SOFTWARE for Fail-Safe Cooling Strategy details.

Scheme 224

Differential Pressure Feedback EGR Sensor

For information on the differential pressure feedback EGR sensor, refer to DIFFERENTIAL PRESSURE FEEDBACK EGR SYSTEM .

Engine Coolant Temperature Sensor

The engine coolant temperature (ECT) sensor (Scheme 225) is a thermistor device in which resistance changes with temperature. The electrical resistance of a thermistor decreases as the temperature increases, and increases as the temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature.

Thermistor-type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying the resistance of the passive sensor causes a variation in total current flow.

Voltage that is dropped across a fixed resistor in a series with the sensor resistor determines the voltage signal at the PCM. This voltage signal is equal to the reference voltage minus the voltage drop across the fixed resistor.

The ECT measures the temperature of the engine coolant. The sensor is threaded into an engine coolant passage. The ECT sensor is similar in construction to the IAT sensor.

Scheme 225

Engine Fuel Temperature Sensor

The engine fuel temperature (EFT) sensor (Scheme 226) is a thermistor device in which resistance changes with temperature. The electrical resistance of a thermistor decreases as temperature increases, and increases as temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature.

Thermistor-type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying the resistance of the passive sensor causes a variation in total current flow.

Voltage that is dropped across a fixed resistor in series with the sensor resistor determines the voltage signal at the PCM. This voltage signal is equal to the reference voltage minus the voltage drop across the fixed resistor.

The EFT sensor measures the temperature of the fuel near the fuel injectors. This signal is used by the PCM to adjust the fuel injector pulse width and meter fuel to each engine combustion cylinder.

Scheme 226

Engine Oil Temperature Sensor

The engine oil temperature (EOT) sensor (Scheme 227) is a thermistor device in which resistance changes with temperature. The electrical resistance of a thermistor decreases as the temperature increases and increases as the temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature.

Thermistor-type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying the resistance of the passive sensor causes a variation in total current flow.

Voltage that is dropped across a fixed resistor in a series with the sensor resistor determines the voltage signal at the PCM. This voltage signal is equal to the reference voltage minus the voltage drop across the fixed resistor.

The EOT sensor measures the temperature of the engine oil. The sensor is typically threaded into the engine oil lubrication system near the oil filter or screwed into the oil pan. The PCM can use the EOT sensor input to determine the following

1. On Variable Cam Timing (VCT) applications the EOT input is used to adjust the VCT control gains and logic for camshaft timing.
2. The PCM can use EOT sensor input in conjunction with other PCM inputs to determine oil degradation.
3. The PCM can use EOT sensor input to initiate a soft engine shutdown. To prevent engine damage from occurring as a result of high oil temperatures, the PCM has the ability to initiate a soft engine shutdown. Whenever engine RPM exceeds a calibrated level for a certain period of time, the PCM will begin reducing power by disabling engine cylinders.

Scheme 227

Fuel Level Input

The fuel level input (FLI) is a hard wire signal input to the PCM from the fuel pump (FP) module. Refer to the description of the FLI in the ON BOARD DIAGNOSTICS MONITORS .

Fuel Tank Pressure Sensor

For information on the fuel tank pressure (FTP) sensor, refer to the description of the EVAPORATIVE EMISSION SYSTEMS .

Fuel Rail Pressure Sensor

The fuel rail pressure (FRP) sensor (Scheme 228) is a diaphragm strain gauge device in which resistance changes with pressure. The electrical resistance of a strain gauge increases as pressure increases, and decreases as pressure decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the 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 the resistance of the passive sensor causes a variation in total current flow.

Voltage that is dropped across a fixed resistor in series with the sensor resistor determines the voltage signal at the PCM. This voltage signal is equal to the reference voltage minus the voltage drop across the fixed resistor.

The FRP sensor measures the pressure of the fuel near the fuel injectors. This signal is used by the PCM to adjust the fuel injector pulse width and meter fuel to each engine combustion cylinder.

Scheme 228

The fuel rail pressure (FRP) sensor (Scheme 229) senses the pressure difference between the fuel rail and the intake manifold. The return fuel line to the fuel tank has been deleted in this type of fuel system. The differential fuel/intake manifold pressure together with measured fuel temperature provides an indication of the fuel vapors in the fuel rail. Both differential pressure and temperature feedback signals are used to control the speed of the fuel pump. The speed of the fuel pump sustains fuel rail pressure which preserve fuel in its liquid state. The dynamic range of the fuel injectors increase because of the higher rail pressure, which allows the injector pulse width to decrease.

Scheme 229

Generator Monitor (Gen Mon)

For information on the generator monitor, refer to the description of the PCM/CONTROLLED CHARGING SYSTEM .

Heated Oxygen Sensor

The heated oxygen sensor (HO2S) (Scheme 230) detects the presence of oxygen in the exhaust and produces a variable voltage according to the amount of oxygen detected. A high concentration of oxygen (lean air/fuel ratio) in the exhaust produces a voltage signal less than 0.4 volt. A low concentration of oxygen (rich air/fuel ratio) produces a voltage signal greater than 0.6 volt. The HO2S provides feedback to the PCM indicating air/fuel ratio in order to achieve a near stoichiometric air/fuel ratio of 14.7:1 during closed loop engine operation. The HO2S generates a voltage between 0.0 and 1.1 volts.

Embedded with the sensing element is the HO2S heater. The heating element heats the sensor to temperatures of 800°C (1400°F). At approximately 300°C (600 °F) the engine can enter closed loop operation. The VPWR circuit supplies voltage to the heater and the PCM will turn on the heater by providing the ground when the proper conditions occur. Since model year 1998 a high power HO2S heater and heater control system have been installed on the Stream 1 HO2S sensors of most vehicles. The high power heater reaches closed loop fuel control temperatures faster, which allows closed lop engine operation sooner. The use of this heater requires that the HO2S heater control be duty cycled, to prevent damage to the heater. The 6 ohm design is not interchangeable with new style 3.3 ohm heater. Use the appropriate service part number.

Scheme 230

Intake Air Temperature Sensor

The intake air temperature (IAT) sensor is a thermistor device in which resistance changes with temperature. The electrical resistance of a thermistor decreases as the temperature increases, and increases as the temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature.

Thermistor-type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying the resistance of the passive sensor causes a variation in total current flow.

Voltage that is dropped across a fixed resistor in a series with the sensor resistor determines the voltage signal at the PCM. This voltage signal is equal to the reference voltage minus the voltage drop across the fixed resistor.

The IAT provides air temperature information to the PCM. The PCM uses the air temperature information as a correction factor in the calculation of fuel, spark and air flow.

The IAT sensor provides a quicker temperature change response time than the ECT or CHT sensor.

Currently there are two design types of IAT sensors used, a stand alone\non-integrated type (Scheme 231) and a integrated (Scheme 232) type. Both types function the same, however the integrated type is incorporated into the Mass Air Flow (MAF) sensor instead of being a stand alone sensor.

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

Currently two types of IAT2 sensors are used. A non-integrated screw in type (Scheme 231) and an integrated type, which is part of the Thermal Manifold Absolute Pressure (TMAP) sensor (Scheme 240) The TMAP sensor consists of a IAT thermistor and a manifold absolute pressure (MAP) sensor. The thermistor portion of the TMAP is used for IAT2 function and operates in the same manner as a non-integrated IAT2. For additional information on the MAP portion of the TMAP, refer to the THERMAL MANIFOLD ABSOLUTE PRESSURE SENSOR description and operation.

Scheme 231

Scheme 232

Intake Manifold Runner Control

For information on the intake manifold runner control (IMRC), refer to the description of the INTAKE AIR SYSTEMS .

Intake Manifold Swirl Control

For information on the intake manifold swirl control (IMSC), refer to the description of the INTAKE AIR SYSTEMS .

Intake Manifold Tuning Valve

For information on the intake manifold tuning valve(IMTV), refer to the description of the INTAKE AIR SYSTEMS .

Knock Sensor

The knock sensor (KS) (Scheme 233) is a tuned accelerometer on the engine which converts engine vibration to an electrical signal. The PCM uses this signal to determine the presence of engine knock and to retard spark timing.

Scheme 233

Mass Air Flow Sensor

The mass air flow (MAF) sensor uses a hot wire sensing element to measure the amount of air entering the engine. Air passing over the hot wire causes it to cool. This hot wire is maintained at 200°C (392°F) above ambient temperature as measured by a constant cold wire (Scheme 234) If the hot wire electronic sensing element must be replaced, then the entire assembly must be replaced. Replacing only the element may change the air flow calibration.

Scheme 234

The current required to maintain the temperature of the hot wire is proportional to the air mass flow. The MAF sensor then outputs an analog voltage signal to the PCM proportional to the intake air mass. The PCM calculates the required fuel injector pulse width in order to provide the desired air/fuel ratio. This input is also used in determining transmission electronic pressure control (EPC), shift and torque converter clutch scheduling.

Most MAF sensors have integrated bypass technology (IBT) with an integrated intake air temperature (IAT) sensor.

The MAF sensor is located between the air cleaner and the throttle body or inside the air cleaner assembly.

Scheme 235

Scheme 236

Output Shaft Speed Sensor

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

Power Steering Pressure Switch

The power steering pressure (PSP) switch (Scheme 237) monitors the hydraulic pressure within the power steering system. The PSP switch is a normally closed switch that opens as the hydraulic pressure increases. The PCM uses the input signal from the PSP switch to compensate for additional loads on the engine by adjusting the idle rpm and preventing engine stall during parking maneuvers. Also, the PSP switch signals the PCM to adjust transmission electronic pressure control (EPC) pressure during the increased engine load, for example during parking maneuvers.

Scheme 237

Power Steering Pressure Sensor

The power steering pressure (PSP) sensor (Scheme 238) monitors the hydraulic pressure within the power steering system. The PSP sensor voltage input to the PCM will change as the hydraulic pressure changes. The PCM uses the input signal from the PSP sensor to compensate for additional loads on the engine by adjusting the idle rpm and preventing engine stall during parking maneuvers. Also, the PSP sensor signals the PCM to adjust transmission electronic pressure control (EPC) pressure during the increased engine load, for example during parking maneuvers.

Scheme 238

Power Take-Off Switch and Circuit

The Power Take-Off (PTO) circuit (Scheme 239) is used by the PCM to disable some of the OBD II Monitors during PTO operation. The PTO switch is normally open. When the PTO unit is activated the PTO switch is closed and battery voltage is supplied to the PTO input circuit. This indicates to the PCM that an additional load is being applied to the engine.

When the PTO unit is activated, the PCM disables some OBD-II monitors, which may not function reliably during PTO operation. Without the PTO circuit information to the PCM, false Diagnostic Trouble Codes (DTCs) may be set during PTO operation. Prior to an Inspection/Maintenance test, the vehicle will have to be operated with the PTO disengaged long enough to successfully complete the OBD-II Monitors.

Scheme 239

Thermal Manifold Absolute Pressure Sensor

The Thermal Manifold Absolute Pressure Sensor (TMAP) (Scheme 240) consists of a manifold absolute pressure (MAP) sensor and an integrated thermistor. The MAP portion of the sensor uses a piezo-resistive silicon sensing element to provide a voltage proportional to the absolute pressure in the intake manifold. The thermistor portion of the sensor operates in the same manner as an intake air temperature (IAT) sensor. For additional information on how the IAT sensor operates, refer to the INTAKE AIR TEMPERATURE SENSOR description and operation.

For the 2.3L Ranger and 2.3L PZEV Focus, the TMAP sensor is part of the Exhaust Gas Recirculation (EGR) system. The PCM uses information from the MAP portion of the TMAP sensor, throttle position (TP) sensor, mass air flow (MAF) sensor, engine coolant temperature (ECT) sensor or cylinder head temperature (CHT) sensor and crankshaft position (CKP) sensor to determine how much exhaust gas is introduced into the intake manifold. The thermistor portion of the TMAP sensor is currently not being used on this application.

For the 4.6L SC Mustang, the PCM uses manifold absolute pressure information from the MAP portion of the TMAP sensor along with other sensor inputs to determine the proper amount of fuel needed for combustion under varying engine load conditions. The thermistor portion of the TMAP sensor is used as a second IAT sensor. This second IAT sensor, located after the supercharger, provides manifold air temperature information to the PCM.

Scheme 240

Throttle Position Sensor

The throttle position (TP) sensor (Scheme 241) is a rotary potentiometer sensor that provides a signal to the PCM that is linearly proportional to the throttle plate/shaft position. The sensor housing has a three-blade electrical connector that may be gold plated. The gold plating increases corrosion resistance on terminals and increases connector durability. The TP sensor is mounted on the throttle body. As the TP sensor is rotated by the throttle shaft, four operating conditions are determined by the PCM from the TP. Those conditions are closed throttle (includes idle or deceleration), part throttle (includes cruise or moderate acceleration), wide open throttle (includes maximum acceleration or de-choke on crank), and throttle angle rate.

Scheme 241

Transmission Control Switch

The transmission control switch (TCS) (Scheme 242) and (Scheme 243) signals the PCM with key power whenever the TCS is pressed. On vehicles with this feature, the transmission control indicator lamp (TCIL) lights when the TCS is cycled to disengage overdrive. The operator of the vehicle controls the position of the TCS.

Scheme 242

Scheme 243

Vehicle Speed Sensor

The vehicle speed sensor (VSS) (Scheme 244) is a variable reluctance or Hall-effect sensor that generates a waveform with a frequency that is proportional to the speed of the vehicle. If the vehicle is moving at a relatively low velocity, the sensor produces a signal with a low frequency. As the vehicle velocity increases, the sensor generates a signal with a higher frequency. The PCM uses the frequency signal generated by the VSS (and other inputs) to control such parameters as fuel injection, ignition control, transmission/transaxle shift scheduling and torque converter clutch scheduling.

Scheme 244

4x4 Mode Switch

The generic electronic module (GEM) or the 4x4 module (4x4M) provides the PCM with an indication of 4x4L. This input is used to adjust the shift schedule. A 5.0 volt module pull-up indicates 4x4H or 2WD (Scheme 245)

Scheme 245

PCM Outputs

Note. Transmission outputs which are not described in this article are discussed in the appropriate AUTOMATIC TRANSMISSION article.

Canister Vent Solenoid

For information on the canister vent solenoid, refer to the description of the EVAPORATIVE EMISSION SYSTEM .

Coil Pack

A coil in a coil pack (Scheme 246) is turned on (for example is coil charging) by the PCM, and is turned off when firing two spark plugs at once. The spark plugs are paired so that as one spark plug fires on the compression stroke, the other spark plug fires on the exhaust stroke. The next time the coil is fired the order is reversed. The next pair of spark plugs fire according to the engine firing order.

Coil On Plug

The coil on plug (COP) (Scheme 247) ignition operates similar to standard coil pack ignition except each plug has one coil per plug. COP has three different modes of operation: engine crank, engine running, and CMP Failure Mode Effects Management (FMEM).

Engine Crank/Engine Running

During engine crank the PCM will fire two spark plugs simultaneously. Of the two plugs simultaneously fired one will be under compression the other will be on the exhaust stroke. Both plugs will fire until camshaft position is identified by a successful camshaft position sensor signal. Once camshaft position is identified, only the cylinder under compression will be fired.

CMP FMEM

During CMP FMEM the COP ignition works the same as during engine crank. This allows the engine to operate without the PCM knowing if cylinder one is under compression or exhaust.

Scheme 246

Scheme 247

Electric EGR System (EEGR)

For information on the EEGR system, refer to EXHAUST GAS RECIRCULATION SYSTEMS , Electric EGR System (EEGR).

EGR System Module (ESM)

For information on the ESM system, refer to EXHAUST GAS RECIRCULATION SYSTEMS , EGR System Module (ESM).

EGR Vacuum Regulator Solenoid

For information on the EGR vacuum regulator (EVR) solenoid, refer to EXHAUST GAS RECIRCULATION SYSTEMS , Differential Pressure Feedback EGR System.

Electric Secondary Air Injection Pump

For information on the electric secondary air injection pump, refer to the description of the SECONDARY AIR INJECTION SYSTEMS .

Evaporative Emission Canister Purge Valve

For information on the Evaporative Emission (EVAP) canister purge valve, refer to the description of the EVAPORATIVE EMISSION SYSTEMS .

Fan Control

The PCM monitors certain parameters (such as engine coolant temperature, vehicle speed, A/C on/off status, A/C pressure, etc) to determine engine cooling fan needs.

For Variable Speed Electric Fan(s)

The PCM controls the fan speed and operation using a duty cycle output on the Fan Control - Variable (FCV) circuit. The fan controller (located at or integral to the engine cooling fan assembly) receives the FCV command and operates the cooling fan at the speed requested (by varying the power applied to the fan motor).

CROWN VICTORIA/GRAND MARQUIS, TOWN CAR: FCV DUTY CYCLE OUTPUT FROM PCM (NEGATIVE DUTY CYCLE)

LS6/LS8, THUNDERBIRD: FCV DUTY CYCLE OUTPUT FROM PCM

For Relay Controlled Fans

The PCM controls the fan operation through the Fan Control (FC) (single speed fan applications), Low Fan Control (LFC), Medium Fan Control (MFC) and/or High Fan Control (HFC) outputs.

For three speed fans, although the PCM output circuits are called low, medium and high fan control (FC), cooling fan speed is controlled by a combination of these outputs. Refer to the 2.0L FOCUS (with A/C) and TAURUS/SABLE: PCM FC OUTPUT STATE FOR COOLING FAN SPEEDS table.

2.0L FOCUS (with A/C) and TAURUS/SABLE: PCM FC OUTPUT STATE FOR COOLING FAN SPEEDS

2.0L FOCUS (with A/C) and TAURUS/SABLE: PCM FC OUTPUT STATE FOR COOLING FAN SPEEDS

FREESTAR, MONTEREY: PCM FC OUTPUT STATE FOR COOLING FAN SPEEDS

Fuel Cap Off Indicator Lamp

The Fuel Cap Off Indicator Lamp (FCIL) is an output signal that is controlled by the PCM and will illuminate when the strategy determines that there is a failure in the vapor management system due to the fuel filler cap not being sealed properly. This would be detected by the inability to pull vacuum in the fuel tank, after a fueling event.

Note. The Escape, Freestar/Monterey, Mustang, Thunderbird, Town Car, Lincoln LS6/LS8, Expedition and Navigator do not have a dedicated (separate) output wire from the PCM to the instrument cluster. The PCM commands the FCIL on and off through the BUS +/- circuits (SCP).

Fuel Injectors

For information on the fuel injectors, refer to the description of the FUEL SYSTEMS .

Fuel Pressure Regulator Control Solenoid

For information on the fuel pressure regulator control (FPRC) solenoid, refer to the description of the FUEL SYSTEMS .

Generator Communication (Gen Com)

For information on the generator (Gen Com), refer to the description of PCM/CONTROLLED CHARGING SYSTEM .

High Fan Control

For information on high fan control, refer to FAN CONTROL .

Idle Air Control Solenoid

For information on the idle air control solenoid, refer to the description of the INTAKE AIR SYSTEMS .

For information on the intake manifold runner control, refer to the description of the INTAKE AIR SYSTEMS .

For information on the intake manifold swirl control, refer to the description of the INTAKE AIR SYSTEMS .

For information on the intake manifold tuning valve, refer to the description of the INTAKE AIR SYSTEMS .

Low Fan Control

For information on low fan control, refer to FAN CONTROL .

Medium Fan Control

For information on medium fan control, refer to FAN CONTROL .

Secondary Air Injection Bypass Solenoid

For information on the secondary air injection bypass solenoid, refer to the description of the SECONDARY AIR INJECTION SYSTEMS .

Transmission Control Indicator Lamp

The transmission control indicator lamp (TCIL) is an output signal from the PCM that controls the lamp on/off function depending on the engagement or disengagement of overdrive. Refer to TRANSMISSION CONTROL SWITCH in Hardware PCM Inputs.

Wide Open Throttle A/C Cut-Off (WAC)

The wide open throttle A/C cutoff relay (may be referred to as the A/C clutch relay) is wired normally open (normally closed for Aviator). There is no direct electrical connection between the A/C switch or EATC Module and the A/C clutch. The PCM will receive a signal indicating that A/C is requested (for some applications, this message is sent through the BUS + and BUS - circuits). When A/C is requested, the PCM will check other A/C related inputs that are available (such as ACP (SW), ACCS). If these inputs indicate A/C operation is OK, and the engine conditions are OK (such as coolant temperature, engine rpm, throttle position), the PCM will ground the WAC output (unground for Aviator), closing the relay contacts and sending voltage to the A/C clutch.

Vapor Management Valve (VMV)

For information on the vapor management valve (EVAP canister purge valve), refer to the description of the EVAPORATIVE EMISSION SYSTEMS .

Powertrain Control Module - Vehicle Speed Output (VSO)

The PCM-VSO (Powertrain Control Module - Vehicle Speed Output) speed signal subsystem generates vehicle speed information for distribution to the vehicle's electrical/electronic modules and subsystems that require vehicle speed data. This subsystem senses the transmission output shaft speed with a sensor. The data is processed by the PCM, and distributed as a hard-wired signal or as a message on the vehicle communication network (SCP or HSCAN).

The key features of the PCM-VSO system are to

1. Infer vehicle movement from the output shaft sensor signal
2. Convert transmission output shaft rotational information to vehicle speed information
3. Compensate for tire size and axle ratio with a programmed calibration variable
4. Utilize a transfer case sensor for four wheel drive applications
5. Distribute vehicle speed information as a multiplexed message and/or an analog signal

The signal from a non-contact shaft sensor (Output Shaft Sensor-OSS or Transfer Case Shaft Sensor-TCSS) mounted on the transmission (automatics, manuals, or 4X4 transfer cases) is sensed directly by the PCM. The PCM converts the OSS or TCSS information to 8000 pulses per mile, based on a tire and axle ratio conversion factor. This conversion factor is programmed into the PCM at the time the vehicle is assembled and can be reprogrammed in the field for servicing changes in the tire size and axle ratio. The PCM transmits the computed vehicle speed and distance traveled information to all the vehicle speed signal users on the vehicle. VSO information can be transmitted by a hard-wired interface between the vehicle speed signal user and the PCM, or by Speed and Odometer data message via the vehicle communication network data link.

The VSO hard -wired signal wave form is a DC square wave with a voltage level of 0 to VBAT. Typical output operating range is 2.22 Hz per MPH (1.3808 Hz pr 1 Km/h).

The Integrated Electronic Ignition (EI) system consists of a crankshaft position (CKP) sensor, coil pack(s), connecting wiring, and PCM. The Coil On Plug (COP) Integrated EI System uses a separate coil per spark plug and each coil is mounted directly onto the plug. The COP Integrated EI System eliminates the need for spark plug wires but does require input from the camshaft position (CMP) sensor. Operation of the components are as follows (Scheme 248)

Scheme 248

Scheme 249

1. The CKP sensor is used to indicate crankshaft position and speed by sensing a missing tooth on a pulse wheel mounted to the crankshaft. The CMP sensor is used by the COP Integrated EI System to identify top dead center of compression of cylinder 1 to synchronize the firing of the individual coils.
2. The PCM uses the CKP signal to calculate a spark target and then fires the coil pack(s) to that target shown (Scheme 249) The PCM uses the CMP sensor not (Scheme 249)on COP Integrated EI Systems to identify top dead center of compression of cylinder 1 to synchronize the firing of the individual coils.
3. The coils and coil packs receive their signal from the PCM to fire at a calculated spark target. Each coil within the pack fires two spark plugs at the same time. The plugs are paired so that as one fires during the compression stroke the other fires during the 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 the compression stroke. The PCM acts as an electronic switch to ground in the coil primary circuit. When the switch is closed, battery positive voltage (B+) applied to the coil primary circuit builds a magnetic field around the primary coil. When the switch opens, the power is interrupted and the primary field collapses inducing the high voltage in the secondary coil windings and the spark plug is fired. A kickback voltage spike occurs when the primary field collapses. The PCM uses this voltage spike to generate an Ignition Diagnostic Monitor (IDM) signal. IDM communicates information by pulsewidth modulation in the PCM.
4. The PCM processes the CKP signal and uses it to drive the tachometer as the Clean Tach Out (CTO) signal.

Crankshaft Position Sensor

The crankshaft position (CKP) sensor (Scheme 250) is a magnetic transducer mounted on the engine block adjacent to a pulse wheel located on the crankshaft. By monitoring the crankshaft mounted pulse wheel, the CKP is the primary sensor for ignition information to the PCM. The pulse wheel has a total of 35 teeth spaced 10 degrees apart with one empty space for a missing tooth. The 6.8L ten cylinder pulse wheel has 39 teeth spaced 9 degrees apart and one 9 degree empty space for a missing tooth. By monitoring the pulse wheel, the CKP sensor signal indicates crankshaft position and speed information to the PCM. By monitoring the missing tooth, the CKP sensor is also able to identify piston travel in order to synchronize the ignition system and provide a way of tracking the angular position of the crankshaft relative to a fixed reference (Scheme 248) for the CKP sensor configuration. The PCM also uses the CKP signal to determine if a misfire has occurred by measuring rapid decelerations between teeth.

Scheme 250

The camshaft position sensor (Scheme 251) used by COP Integrated EI system is a magnetic transducer mounted on the engine front cover adjacent to the camshaft. By monitoring a target on the camshaft sprocket, the CMP sensor identifies cylinder one to the PCM. The COP Integrated EI system uses this information to synchronize the firing of the individual coils.

Scheme 251

Coil packs come in four tower, Series 5 four tower, six-tower horizontal connector and Series 5 Six tower models. Two adjacent coil towers share a common coil and are called a matched pair. For six-tower coil pack (six cylinder) applications the matched pairs are 1 and 5, 2 and 6, and 3 and 4 (Scheme 252) and (Scheme 253) For four-tower coil pack (four cylinder) applications the matched pairs are 1 and 4, and 2 and 3 (Scheme 254) and (Scheme 255)

When the coil is fired by the PCM, spark is delivered through the matched pair towers to their respective spark plugs. The spark plugs are fired simultaneously and are paired so that as one fires on the compression stroke, the other spark plug fires on the exhaust stroke. The next time the coil is fired the situation is reversed. The next pair of spark plugs fire according to the engine firing order.

Scheme 252

Scheme 253

Scheme 254

Scheme 255

The coil on plug (COP) (Scheme 256) ignition operates similar to standard coil pack ignition except each plug has one coil per plug. COP has three different modes of operation: engine crank, engine running, and CMP Failure Mode Effects Management (FMEM).

Scheme 256

During engine crank the PCM will fire two spark plugs simultaneously. Of the two plugs simultaneously fired one will be under compression the other will be on the exhaust stroke. Both plugs will fire until camshaft position is identified by a successful camshaft position sensor signal. Once camshaft position is identified only the cylinder under compression will be fired.

During CMP FMEM the COP ignition works the same as during engine crank. This allows the engine to operate without the PCM knowing if cylinder one is under compression or exhaust.

Returnable Fuel System

The fuel system consists of a fuel tank with a reservoir, fuel pump module, fuel supply lines, fuel filter(s), Schrader/pressure test point, fuel rail, fuel injectors, and fuel pressure regulator. Operation of the system is as follows (refer to (Scheme 257) for all others)

1. The fuel delivery system uses the crankshaft position (CKP) sensor to signal the PCM that the engine is either cranking or running.
2. The fuel pump logic is defined in the Fuel System control strategy and is executed in the PCM. The PCM will ground the fuel pump relay for one second during key on and engine off. During crank the fuel pump relay is grounded as long as the PCM receives a CKP signal.
3. The fuel pump relay has a primary and a secondary circuit. The primary side is controlled by the PCM and the secondary side provides B+ to the fuel pump circuit when the relay is energized.
4. The inertia fuel shut-off (IFS) switch is used to de-energize the fuel delivery secondary circuit in the event of a collision. The IFS Switch is a safety device that should only be reset after a thorough inspection of the vehicle (following a collision).
5. The fuel injector is a solenoid-operated valve that meters fuel flow to each combustion cylinder. The fuel injector is opened and closed a constant number of times per crankshaft revolution. The amount of fuel is controlled by length of time the fuel injector is held open. The injector is normally closed and is operated by 12 volt VPWR from the power relay. The ground signal is controlled by the PCM.
6. A pressure test point valve (Schrader valve) is located on the 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 the fuel rail downstream of the fuel injectors. It regulates fuel pressure supplied to the fuel injectors. The fuel pressure regulator is a diaphragm-operated relief valve. One side of the diaphragm senses fuel pressure and the other side is connected to the intake manifold vacuum. Fuel pressure is established by a spring preload applied to the diaphragm. Balancing one side of the diaphragm with manifold vacuum maintains a constant fuel pressure drop across the fuel injectors. Fuel pressure is high when engine vacuum is low. Excess fuel is bypassed through the fuel pressure regulator and returned through the fuel return line to the fuel tank.
8. There are four filtering or screening devices in the fuel delivery system. The fuel intake sock or screen is a fine, nylon mesh mounted on the intake side of the fuel pump. There is a fuel filter screen located at the fuel rail side of the fuel injector. A fuel filter/screen is located in the inlet side of the fuel pressure regulator. The fuel filter assembly is located between the fuel pump and the 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 the reservoir and supplies fuel through the fuel pump module manifold to the engine and the fuel pump module jet pump.

Note. Some vehicles have the relay located in the Power Distribution Box.

Scheme 257

Mechanical Returnless Fuel System

The 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 (if equipped), fuel injectors, and Schrader/pressure test point. Operation of the system is as follows (Scheme 258)

1. The fuel delivery system is enabled during crank or running mode once the 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 the PCM.
3. The PCM grounds the fuel pump relay, which provides VPWR to the fuel pump.
4. The inertia fuel shut-off (IFS) switch is used to de-energize the fuel delivery secondary circuit in the event of collision. The IFS switch is a safety device that should only be reset after a thorough inspection of the vehicle (following a collision).
5. A pressure test point valve (Schrader valve) is located on the fuel rail. This is used to measure fuel injector supply pressure for diagnostic procedures and repairs. ON VEHICLES NOT EQUIPPED WITH A SCHRADER VALVE, USE ROTUNDA FUEL PRESSURE TEST KIT #134-R0087 OR EQUIVALENT.
6. Located on the fuel rail is a pulse damper (if equipped). The pulse damper reduces fuel system noise caused by the pulsing of the fuel injectors. The vacuum port located on the damper is connected to manifold vacuum to avoid fuel spillage in the event the pulse damper diaphragm were to rupture (the pulse damper should not be confused with a fuel pressure regulator).
7. The fuel injector is a solenoid-operated valve that meters the fuel flow to each combustion cylinder. The fuel injector is opened and closed a constant number of times per crankshaft revolution. The amount of fuel is controlled by the length of time the fuel injector is held open. The injector is normally closed and is operated by 12 volt VPWR from the power relay. The ground signal is controlled by the PCM.
8. There are three filtering or screening devices in the fuel delivery system. The intake sock is a fine, nylon mesh screen mounted on the intake side of the fuel pump. There is a fuel filter screen located at the fuel rail side of the fuel injector. The fuel filter assembly is located between the fuel pump and the pressure test point/Schrader valve.
9. The fuel pump (FP) module contains the fuel pump, fuel pressure regulator and the fuel sender assembly. The fuel pressure regulator is attached to the fuel pump in the fuel pump module located in the fuel tank. It regulates fuel pressure supplied to the fuel injectors. The fuel pressure regulator is a diaphragm-operated relief valve. Fuel pressure is established by a spring preload applied to the diaphragm. Excess fuel is bypassed through the regulator and returned to the fuel tank.

Scheme 258

Electronic Returnless Fuel System

The 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. Operation of the system is as follows (Scheme 259) and (Scheme 260)

1. The fuel delivery system is enabled during crank or running mode once the 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 the PCM.
3. The PCM commands a duty cycle to the fuel pump driver module (FPDM).
4. The fuel pump driver module modulates the voltage to the fuel pump (FP) to achieve the proper fuel pressure. Voltage for the fuel pump is supplied by the power relay or FPDM power supply relay. (For additional information on FPDM operation, refer to «PCM OUTPUTS»(ref-227199-S02373774962006033000000) - «FUEL PUMP»(ref-227199-S27915475242006033000000) and «PCM INPUTS»(ref-227199-S19237715052006033000000) -FPM.)
5. The fuel rail pressure (FRP) sensor provides the PCM with the current fuel rail pressure. The PCM uses this information to vary the duty cycle output to the FPDM to compensate for varying loads.
6. The engine fuel temperature (EFT) sensor measures current fuel temperatures in the fuel rail. This information is used to vary the fuel pressure and avoid fuel system vaporization.
7. The fuel injector is a solenoid-operated valve that meters the fuel flow to each combustion cylinder. The fuel injector is opened and closed a constant number of times per crankshaft revolution. The amount of fuel is controlled by the length of time the fuel injector is held open. The injector is normally closed and is operated by 12 volt VPWR from the power relay. The ground signal is controlled by the PCM.
8. A pressure test point valve (Schrader valve) is located on the fuel rail. This is used to measure fuel injector supply pressure for diagnostic procedures and repairs. ON VEHICLES NOT EQUIPPED WITH A SCHRADER VALVE, USE ROTUNDA FUEL PRESSURE TEST KIT #134-R0087 OR EQUIVALENT.
9. There are three filtering or screening devices in the fuel delivery system. The intake sock is a fine, nylon mesh screen mounted on the intake side of the fuel pump. There is a fuel filter screen located at the fuel rail side of the fuel injector. The fuel filter assembly is located between the fuel pump and the pressure test point/Schrader valve.
10. The fuel pump (FP) module is a device that contains the fuel pump and the fuel sender assembly. The fuel pump is located inside the reservoir and supplies fuel through the fuel pump module manifold to the engine and the fuel pump module jet pump.
11. The inertia fuel shut-off (IFS) switch is used to de-energize the fuel delivery secondary circuit in the event of a collision. The IFS switch is a safety device that should only be reset after a thorough inspection of the vehicle (following a collision).

Scheme 259

Scheme 260

Fuel Pump and Reservoir

The fuel pump module (Scheme 261) is mounted inside the fuel tank in a reservoir. The pump has a discharge check valve that maintains system pressure after the ignition key has been turned off to minimize starting concerns. The reservoir prevents fuel flow interruptions during extreme vehicle maneuvers with low tank fill levels.

Scheme 261

Fuel Pump Module

The fuel pump (FP) module ( (Scheme 262), (Scheme 263) and (Scheme 264) ) is a device that contains the fuel pump and sender assembly. The fuel pump is located inside the FP module reservoir and supplies fuel through the FP module manifold to the engine and FP module jet pump. The jet pump continuously refills the reservoir with fuel, and a check valve located in the manifold outlet maintains system pressure when the fuel pump is not energized. A flapper valve located in the bottom of the reservoir allows fuel to enter the reservoir and prime the fuel pump during the initial fill.

Scheme 262

Scheme 263

Scheme 264

Fuel Filters

The system contains four filtering or screening devices. Refer to the individual component pictorial for location.

1. The fuel intake sock or screen is a fine nylon mesh sock mounted on the intake side of the fuel pump. It is part of the assembly and cannot be serviced separately.
2. The filter/screen at the fuel rail port of the Injectors is part of the fuel injector assembly and cannot be serviced separately.
3. The filter/screen at fuel inlet side of the fuel pressure regulator is part of the regulator assembly and cannot be serviced separately.
4. The fuel filter assembly is located between the fuel pump (tank) and the pressure test point (Schrader valve) or Injectors. This filter may be serviced.

Fuel Injector

The fuel injector (Scheme 265) is a solenoid-operated valve that meters fuel flow to the engine. The fuel injector is opened and closed a constant number of times per crankshaft revolution. The amount of fuel is controlled by the length of time the fuel injector is held open.

The fuel injector is normally closed and is operated by 12 volt VPWR from the electronic engine control power relay. The ground signal is controlled by the PCM.

The injector is the deposit resistant injection (DRI) type and does not have to be cleaned. However, it can be flow checked and, if found outside of specification, the fuel injector should be replaced.

Scheme 265

Fuel Pressure Regulator

The fuel pressure regulator, also referred to as the pulse damper, is mounted to the fuel pump bracket within the fuel tank. It regulates fuel pressure supplied to fuel injectors. (Scheme 266)

Scheme 266

Fuel Rail Pulse Damper

The fuel rail pulse damper located on the fuel rail reduces fuel system noise caused by the pulsing of the fuel injectors. The vacuum port located on the damper is connected to manifold vacuum to avoid fuel spillage in the event the pulse damper diaphragm were to rupture. (The pulse damper should not be confused with a fuel pressure regulator, it does not regulate fuel rail pressure.)

Inertia Fuel Shutoff (IFS) Switch

The inertia fuel shutoff (IFS) switch (Scheme 267) is used in conjunction with the electric fuel pump. The purpose of the IFS switch is to shut off the fuel pump if a collision occurs. It consists of a steel ball held in place by a magnet. When a sharp impact occurs, the ball breaks loose from the magnet, rolls up a conical ramp and strikes a target plate which opens the electrical contacts of the switch and shuts off the electric fuel pump. Once the switch is open, it must be manually reset before restarting the vehicle. Refer to the Owner Guide for the location of the IFS.

Scheme 267

Natural Gas Fuel System

The fuel system consists of a fuel tank, fuel shut-off valve assemblies, fuel supply lines, fuel filter, Schrader/service valve, manual fuel shut-off valve, fuel rail, and fuel pressure regulator. Operation of the system is as follows ( (Scheme 268), (Scheme 269) and (Scheme 270) )

1. The fuel delivery system uses the crankshaft position (CKP) sensor to signal the PCM that the engine is either cranking or running.
2. The fuel shut-off valve logic is defined in the Fuel System control strategy and is executed in the PCM. The PCM will ground the fuel pump relay for one second during key on and engine off. During crank the fuel pump relay is grounded as long as the PCM receives a signal from the CKP.
3. The fuel pump relay has a primary and a secondary circuit. The primary side is controlled by the PCM and the secondary side provides B+ to the fuel shut-off valve circuit when the relay is energized.
4. The inertia fuel shut-off (IFS) switch is used to de-energize the fuel delivery circuit in the event of a collision. The IFS switch is a safety device that should only be reset after a thorough inspection of the vehicle (following a collision).
5. The fuel injector is used to meter natural gas to each combustion cylinder. Although the NG fuel injector appears very similar to some gasoline fuel injectors, it is unique. Flow capacity of this fuel injector is 6 to 12 times as large as various gasoline fuel injectors.
6. The fuel tank shut-off solenoid valve is located in the fuel tank. The solenoid valves are on the same circuit as the fuel pump and utilize the same inertia fuel shut-off (IFS) switch as gasoline.
7. The high pressure fuel filter is used to protect the engine fuel system components. A natural gas coalescing and particulate filter is positioned on the high pressure side of the fuel system just prior to the fuel pressure regulator.
8. The fuel pressure regulator used on the NG vehicle is a single-staged pressure reducing regulator which expands natural gas from storage pressures of 1,379 to 20,685 kPa (200 to 3,000 psig) to engine fuel pressures of 724 to 862 kPa (105 to 125 psig).
9. The fuel rail shut-off valve is a normally closed solenoid actuated valve that opens when grounded by the PCM. The valve isolates the fuel injectors from fuel line pressure when the engine is not operating. The fuel rail shut-off valve is wired in parallel with the fuel tank shut-off solenoid valves.

Scheme 268

Scheme 269

Scheme 270

Fuel Rail

The fuel rail (Scheme 271) distributes low pressure fuel from the chassis supply line to each fuel injector. Fuel pressure at the top of each fuel injector is maintained within 1% of the other fuel injectors at all times; this is done with nearly symmetric flow paths. The fuel rail is also designed to have minimal flow restriction by increasing the cross-sectional flow area and reducing the flow path length. The fuel rail contains several other parts in assembly (PIA) components that perform crucial functions. These include

1. Injection pressure sensor which measures the pressure of the fuel near the fuel injectors. This signal is used by the PCM to adjust the fuel injector pulsewidth and meter fuel to each engine combustion cylinder.
2. Engine fuel temperature sensor which measures the pressure of the fuel near the fuel injectors. This signal is used by the PCM to adjust the fuel injector pulsewidth and meter fuel to each engine combustion cylinder.
3. Low pressure solenoid shut-off valve which isolates the fuel rail from the upstream fuel system when the engine is OFF. This minimizes the amount of fuel available to flow through the fuel injectors when the engine is off or leak from a damaged fuel rail during and after a crash. The valve is controlled by the 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 the PCM.
4. Schrader/service valve (if equipped) provides a service port to the low pressure fuel system. This valve is needed to relieve the pressure in the system before and during service. This valve could also be used to monitor the pressure near the injectors during diagnostic procedures.

Scheme 271

Fuel Injector(s)

The fuel injector (Scheme 272) is a solenoid-operated valve that meters fuel flow to the engine. The fuel injector is opened and closed every other crankshaft revolution. The amount of fuel is controlled by the length of time the fuel injector is held open.

The fuel injector is normally closed and is operated by 12 volt VPWR from the power relay. The ground signal is controlled by the PCM.

The fuel injectors are used to meter natural gas to each combustion cylinder. Although the natural gas fuel injectors appear very similar to some gasoline fuel injectors, they are unique. Flow capacity of these fuel injectors is 6 to 12 times as large as various gasoline fuel injectors. Electrical resistance is much lower than typical gasoline fuel injectors (4.6 ohms as opposed to 14.5 ohms). To accommodate this lower resistance, a fuel injector driver module is used to convert the PCM fuel injector driver signal to the signal required by the fuel injector.

Scheme 272

The fuel pressure regulator (Scheme 273) used in the Natural Gas fuel system is a single-stage pressure reducing regulator which expands natural gas from storage pressures of 1,379 to 20,685 kPa (200 to 3,000 psig) to engine fuel injector pressures of 724 to 862 kPa (105 to 125 psig).

The regulator contains a pressure relief device, a 1,896 kPa (275 psig) check valve, which protects the low pressure fuel system. The low pressure fuel system no longer must fulfill the design requirements of the high pressure fuel system, therefore reducing cost, weight and complexity.

When gas expands, the fuel temperature drops significantly causing extreme cold temperatures (-177°C or -160°F) that may damage synthetic fuel system components as well as cause water vapor within the fuel to condense, freeze and plug the lines, valve and injectors. To prevent this, engine coolant is routed through the fuel pressure regulator to warm the fuel before it expands.

The regulator has an internal thermostat in its coolant bowl to control the flow of engine coolant. This prevents overheating and subsequent thinning of the fuel which may cause lean combustion. Outlet coolant flow is restricted by the thermostat when it rises above approximately 82°C (100°F). If service of the coolant bowl and/or thermostat is required, the coolant bowl and thermostat are serviced separately (9G735)

Scheme 273

High Pressure Fuel Filter

The high pressure fuel filter (Scheme 274) is used to protect the engine fuel system components. A natural gas coalescing and particulate filter is positioned on the high pressure side of the fuel system just prior to the pressure regulator. The filter is part of the regulator assembly. The filter can be disassembled to service the element. The drain plug on the bottom of the housing can be removed to drain any water that accumulates.

Scheme 274

Fuel Lines and Fittings

A fuel line assembly (Scheme 275) 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 the 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 the fuel rail. The other fittings used on the natural gas vehicle to connect fuel components are SAE O-ring face seal tube fittings. There are two 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.

Scheme 275

Fuel Tank Shutoff Valve

The fuel tank shutoff solenoid valve (Scheme 276) is located in the fuel tank. The solenoid valves are on the same circuit as the gasoline fuel pump and utilize the same Inertia fuel shutoff (IFS) switch as gasoline. When the key is in the off position, the shutoff valves are closed and fuel in the tanks is isolated. During refueling, the shutoff valve acts as a check valve and allows flow due to pressure differential between the fuel being added from the fill station and the fuel in the tank.

The internal solenoid valves also have the capability of being "manually locked down." If, while servicing the vehicle, it becomes necessary to remove the fuel tank, the lock down feature provides an added measure of safety. In addition, the valve has an internal Canadian Gas Association (CGA) type 9 fusible link pressure relief device (PRD) that senses the internal fuel tank gas temperature. The contents in the tank are vented when the internal fuel tank gas temperature reaches 103°C (217°F) and melts the fusible link. The escaping gas is vented through a vent line to the atmosphere.

Scheme 276

The inertia fuel shutoff (IFS) switch (Scheme 277) is used in conjunction with electric fuel close valves. The purpose of the IFS switch is to close the fuel shut-off valves if a crash occurs. It consists of a steel ball held in place by a magnet. When a sharp impact occurs, the ball breaks loose from the magnet, rolls up a conical ramp and strikes a target plate which opens the electrical contacts of the switch and closes the electric fuel shut-off valve. Once the switch is open, it must be manually reset before restarting the vehicle. On some vehicles a fuel reset light illuminates. Refer to the Owner Guide for the location of the IFS.

Scheme 277

Fuel Rail Shut-Off Valve

The fuel rail shut-off valve see scheme 92 is a normally closed solenoid actuated valve that opens when (along with all of the tank valves) Pin 80 is grounded by the PCM. The valve isolates the fuel injectors from fuel line pressure when the engine is off. Nominal resistance of the coil is 11 ohms. The fuel rail shut-off valve is wired in parallel with the four tank valves.

Differential Pressure Feedback EGR System

The Differential Pressure Feedback EGR system consists of a differential pressure feedback EGR sensor, EGR vacuum regulator solenoid, EGR valve, orifice tube assembly, powertrain control module (PCM) and connecting wires and vacuum hoses. Operation of the system is as follows (Scheme 278)

1. Signals from the engine coolant temperature (ECT) sensor or cylinder head temperature (CHT) sensor, intake air temperature (IAT) sensor, throttle position (TP) sensor, mass air flow (MAF) sensor and crankshaft position (CKP) sensor provide information on engine operating conditions to the PCM. The engine must be warm, stable and running at a moderate load and rpm before the EGR system is activated. The PCM deactivates EGR during idle, extended wide open throttle or whenever a failure is detected in an EGR component or EGR required input.
2. The PCM calculates the desired amount of EGR flow for a given engine condition. It then determines the desired pressure drop across the metering orifice required to achieve that flow and outputs the corresponding signal to the EGR vacuum regulator solenoid.
3. The EGR vacuum regulator solenoid receives a variable duty cycle signal (0 to 100%). The higher the duty cycle the more vacuum the solenoid diverts to the EGR valve.
4. The increase in vacuum acting on the EGR valve diaphragm overcomes the valve spring and begins to lift the EGR valve pintle off its seat, causing exhaust gas to flow into the intake manifold.
5. Exhaust gas flowing through the EGR valve must first pass through the EGR metering orifice. With one side of the orifice exposed to exhaust backpressure and the other to the intake manifold, a pressure drop is created across the orifice whenever there is EGR flow. When the EGR valve closes, there is no longer flow across the metering orifice and pressure on both sides of the orifice is the same. The PCM constantly targets a desired pressure drop across the metering orifice to achieve the desired EGR flow.
6. The differential pressure feedback EGR sensor measures the actual pressure drop across the metering orifice and relays a proportional voltage signal (0 to 5 volts) to the PCM. The PCM uses this feedback signal to correct for any errors in achieving the desired EGR flow.

Scheme 278

The differential pressure feedback EGR sensor (Scheme 279) is a ceramic, capacitive-type pressure transducer that monitors the differential pressure across a metering orifice located in the orifice tube assembly. The differential pressure feedback sensor receives this signal through two hoses referred to as the downstream pressure hose (REF SIGNAL) and upstream pressure hose (HI SIGNAL). The HI and REF hose connections are marked on the differential pressure feedback EGR sensor housing for identification (note that the HI signal uses a larger diameter hose). The differential pressure feedback EGR sensor outputs a voltage proportional to the pressure drop across the metering orifice and supplies it to the PCM as EGR flow rate feedback.

Scheme 279

Tube Mounted Differential Pressure Feedback EGR Sensor

The tube mounted differential pressure feedback EGR sensor (Scheme 280) is identical in operation as the larger metal or plastic DPFE sensors and uses a 1.0 volt offset. The HI and REF hose connections are marked on the underside of the sensor.

Scheme 280

The EGR vacuum regulator solenoid (EVR), (Scheme 281) is an electromagnetic device which is used to regulate the vacuum supply to the EGR valve. The solenoid contains a coil which magnetically controls the position of a disc to regulate the vacuum. As the duty cycle to the coil increases, the vacuum signal passed through the solenoid to the EGR valve also increases. Vacuum not directed to the EGR valve is vented through the solenoid vent to atmosphere. Note that at 0% duty cycle (no electrical signal applied), the EGR vacuum regulator solenoid allows some vacuum to pass, but not enough to open the EGR valve.

Scheme 281

Scheme 282

EGR VACUUM REGULATOR SOLENOID DATA

Exhaust Gas Recirculation Valve

The EGR valve (Scheme 283) in the Differential Pressure Feedback EGR system is a conventional, vacuum-actuated EGR valve. The valve increases or decreases the flow of exhaust gas recirculation. As vacuum applied to the EGR valve diaphragm overcomes the spring force, the valve begins to open. As the vacuum signal weakens, at 5.4 kPa (1.6 in-Hg) or less, the spring force closes the valve. The EGR valve is fully open at about 15 kPa (4.5 in-Hg).

Since EGR flow requirement varies greatly, providing service specifications on flow rate is impractical. The on-board diagnostic system monitors the EGR valve function and triggers a Diagnostic Trouble Code if the test criteria is not met. The EGR valve flow rate is not measured directly as part of the field diagnostic procedures.

Scheme 283

Scheme 284

Highlights of the Electric System

1. EEGR valve is activated by an electric stepper motor and does not use vacuum to control the physical movement of the valve.
2. No vacuum diaphragm is used.
3. No DPFE sensor is used.
4. No Orifice Tube/Assembly is used.
5. No EGR EVR solenoid is used.
6. A new MAP sensor called a TMAP is used, where the temperature function is used as a second IAT in certain applications.
7. Engine coolant is routed through the assembly extending durability of the electric motor.

Hardware

The EEGR valve (Scheme 285) and (Scheme 286) is a water cooled motor/valve assembly. The motor is commanded to move in 52 discrete steps as it acts directly on the EEGR valve. The position of the valve determines the rate of EGR. The built in spring works to close the valve (against the motor opening force).

Scheme 285

Scheme 286

Enhanced Evaporative Emission (EVAP) System

The Enhanced EVAP system (Scheme 287) 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, powertrain control module (PCM) and connecting wires and fuel vapor hoses.

1. The Enhanced EVAP system uses inputs from the engine coolant temperature (ECT) sensor or cylinder head temperature (CHT) sensor, the intake air temperature (IAT) sensor, the mass air flow (MAF) sensor, the vehicle speed sensor (VSS) and the fuel tank pressure (FTP) sensor to provide information about engine operating conditions to the PCM. The fuel level input (FLI) and FTP sensor signals to the PCM are used by the PCM to determine activation of the EVAP leak check Monitor based on presence of vapor generation or fuel sloshing.
2. The PCM determines the desired amount of purge vapor flow to the intake manifold for a given engine condition. The PCM can then output the required signal to the EVAP canister purge valve. The PCM uses the Enhanced EVAP system inputs to evacuate the system using the EVAP canister purge valve, seals the Enhanced EVAP system from atmosphere using the CV solenoid, and uses the FTP sensor to observe total vacuum lost for a period of time.
3. The canister vent (CV) solenoid seals the Enhanced EVAP system to atmosphere during the EVAP leak check Monitor.
4. The PCM outputs a variable duty cycle signal (between 0% and 100%) to the solenoid on the EVAP canister purge valve. On applications with Electronic EVAP Canister Purge Valve, the PCM outputs a variable current (between 0 mA and 1000 mA).
5. The fuel tank pressure (FTP) sensor monitors the fuel tank pressure during engine operation and continuously transmits an input signal to the PCM. During the EVAP monitor testing, the FTP sensor monitors the fuel tank pressure or vacuum bleed-up.
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 the Enhanced EVAP system to control the flow of fuel vapor entering the engine. All of these valves also prevent fuel tank overfilling during refueling operation and prevent liquid fuel from entering the EVAP canister and the EVAP canister purge valve under any vehicle altitude, handling or rollover condition.
7. The Enhanced EVAP system, including all the fuel vapor hoses, can be checked when a leak is detected by the PCM. Refer to the appropriate EVAPORATIVE EMISSIONS article for information on leak detection tools and procedures.

Scheme 287

EVAP Canister Purge Valve

The EVAP canister purge valve (Scheme 288) is part of the Enhanced EVAP system that is controlled by the PCM. This valve controls the flow of vapors (purging) from the EVAP canister to the intake manifold during various engine operating modes. The EVAP canister purge valve is normally closed valve. The electronic EVAP canister purge valve (Scheme 289) controls the flow of vapors electronically by way of a solenoid thereby, eliminating the need for an electronic vacuum regulator and vacuum diaphragm. The PCM outputs a signal between 0% and 100% duty cycle to control the EVAP canister purge valve. On applications with Electronic EVAP canister purge valve, the PCM outputs a signal between 0 mA and 1000 mA to control the solenoid.

Scheme 288

Scheme 289

The fuel tank pressure (FTP) sensor (Scheme 290) or inline fuel tank pressure (FTP) sensor (Scheme 291) is used to measure the fuel tank pressure during the EVAP Leak Check Monitor.

Scheme 290

Scheme 291

During the EVAP Leak Check Monitor, the canister vent (CV) solenoid (Scheme 292) seals the EVAP canister from atmospheric pressure. This allows the EVAP canister purge valve to obtain the target vacuum in the fuel tank during the EVAP Leak Check Monitor.

Scheme 292

Intake Manifold Runner Control (IMRC) Electric Actuated System

The Intake Manifold Runner Control (IMRC) Electric Actuated system (Scheme 293) consists of a remote mounted motorized actuator with an attaching cable for each housing on each bank. Some applications will use one cable for both banks. The cable or linkage attaches to the housing butterfly plate levers. The 2.0L (2V) Focus IMRC uses a motorized actuator mounted directly to a single housing without the use of a cable. Each IMRC housing is an aluminum casting with two intake air passages for each cylinder. One passage is always open and the other is opened and closed with a butterfly valve plate. The housing uses a return spring to hold the butterfly valve plates closed. The motorized actuator houses an internal switch or switches, depending on the application, to provide feedback to the PCM indicating cable and butterfly valve plate position.

Below approximately 3000 rpm, the motorized actuator will not be energized. This will allow the cable to fully extend and the butterfly valve plates to remain closed. Above approximately 3000 rpm, the motorized actuator will be energized. The attaching cable will pull the butterfly valve plates into the open position. Some vehicles will activate the IMRC near 1500 rpm.

1. The PCM uses the TP sensor and CKP signals to determine activation of the IMRC system. There must be a positive change in voltage from the TP sensor along with the increase in rpm to open the valve plates.
2. The PCM uses the information from the input signals to control the IMRC motorized actuator based upon rpm and changes in throttle position.
3. The PCM energizes the actuator to pull the butterfly plates open with the cable(s) or linkage.
4. The IMRC housing contains butterfly plates to allow increased air flow.

Scheme 293

Intake Manifold Swirl Control (IMSC) Vacuum Actuated System

The Intake Manifold Swirl Control (IMSC) Vacuum Actuated system (Scheme 294) consists of a manifold mounted vacuum actuator and a PCM controlled electric solenoid. The linkage from the actuator attaches to the manifold butterfly plate lever. The IMSC actuator and manifold are composite/plastic with a single intake air passage for each cylinder. The passage has a butterfly valve plate that blocks 60% of the opening when actuated, leaving the top of the passage open to generate turbulence. The housing uses a return spring to hold the butterfly valve plates open.

The vacuum actuator houses an internal monitor circuit to provide feedback to the PCM indicating butterfly valve plate position.

Below approximately 3000 rpm, the vacuum solenoid will be energized. This will allow manifold vacuum to be applied and the butterfly valve plates to remain closed. Above approximately 3000 rpm, the vacuum solenoid will be deenergized. This will allow vacuum to vent from the actuator and the butterfly valve plates to open.

1. The PCM monitors the TP sensor, CHT and CKP signals to determine activation of the IMSC system. There must be a positive change in voltage from the TP sensor along with the increase in rpm at the proper engine temperature to open the valve plates.
2. The PCM uses the information from the input signals to control the IMSC electric solenoid based upon changes in throttle position, engine temperature and rpm.
3. The PCM energizes the solenoid with the key on engine running, vacuum is then applied to the actuator to pull the butterfly plates closed.

Scheme 294

Intake Manifold Tuning Valve (IMTV)

The intake manifold tuning valve (IMTV) (Scheme 295) is a motorized actuated unit mounted directly to the intake manifold. The IMTV actuator controls a shutter device attached to the actuator shaft. There is no monitor input to the PCM with this system to indicate shutter position.

The motorized IMTV unit will not be energized below approximately 2600 rpm or higher on some vehicles. The shutter will be in the closed position not allowing airflow blend to occur in the intake manifold. Above approximately 2600 rpm or higher, the motorized unit will be energized. The motorized unit will be commanded on by the PCM initially at a 100 percent duty cycle to move the shutter to the open position and then falling to approximately 50 percent to continue to hold the shutter open.

1. The PCM uses the TP sensor and CKP signals to determine activation of the IMTV system. There must be a positive change in voltage from the TP sensor along with the increase in rpm to open the shutter.
2. The PCM uses the information from the input signals to control the IMTV.
3. When commanded on by the PCM, the motorized actuator shutter opens up the end of the vertical separating wall at high engine speeds to allow both sides of the manifold to blend together.

Scheme 295

Throttle Body System Hardware

The major components of the throttle body assembly include the TP sensor, IAC valve assembly, and throttle body housing assembly.

The TP sensor monitors throttle position and provides an electrical signal to the PCM. It is monitored by the OBD system for component integrity, system functionality, and faults that can cause emissions levels to exceed standards set in government regulations. For additional information on the TP sensor, refer to Electronic EC System Hardware - PCM INPUTS .

Idle Air Control Valve

The idle air control (IAC) valve assembly controls engine idle speed and provides a dashpot function. The IAC valve assembly meters intake air around the throttle plate through a bypass within the IAC valve assembly and throttle body. The PCM determines the desired idle speed or bypass air and signals the IAC valve assembly through a specified duty cycle. The IAC valve responds by positioning the IAC valve to control the amount of bypassed air. The PCM monitors engine rpm and increases or decreases the IAC duty cycle in order to achieve the desired rpm.

Note. The IAC Valve Assembly is NOT ADJUSTABLE and CANNOT BE CLEANED.

The IAC valve (part of throttle body assembly) has an internal diode on some applications. If the internal diode is measured in crossed terminal position with a digital multimeter, there will be an incorrect or negative reading. It is important that the mating component and harness connectors are correctly oriented. Diagnostic procedures emphasize this importance.

The PCM uses the IAC valve assembly to control

1. No touch start
2. Cold engine fast idle for rapid warm-up
3. Idle (corrects for engine load)
4. Stumble or stalling on deceleration (provides a dashpot function)
5. Over-temperature idle boost.

Throttle Body Housing

The throttle body housing assembly is a single piece of aluminum casting with an air passage and a butterfly throttle plate with linkage mechanisms. When the throttle plate is in the idle (or closed) position, the throttle lever arm should be in contact with the Throttle Return Stop. The throttle return stop prevents the throttle plate from contacting the bore and sticking closed. The setting also establishes the amount of air flow between the throttle plate and bore. To minimize the closed plate air flow, a special coating is applied to the throttle plate and bore to help seal this area. This sealant/coating also makes the throttle body resistant to engine intake sludge accumulation.

Features of the Throttle Body Assembly include

1. Idle air control (IAC) valve assembly mounted directly to the throttle body assembly (some vehicles).
2. A pre-set stop to locate the WOT position.
3. An air supply channel upstream of the throttle plate to provide fresh air to the PCV system (some vehicles only).
4. Individual vacuum taps for PCV, EGR, EVAP and miscellaneous control signals (some vehicles only).
5. PCV air return (if applicable).
6. A throttle body-mounted throttle position (TP) sensor.
7. A sealant/coating on the throttle bore and throttle plate makes the throttle body air flow tolerant to engine intake sludge accumulation. These throttle body assemblies MUST NOT BE CLEANED and have a white/black attention decal (Scheme 296) advising not to clean.

Scheme 296

Electric Secondary Air Injection System

The 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 bypass solenoid, a AIR relay, powertrain control module (PCM) and connecting wires and vacuum hoses (Scheme 297)

1. The PCM requires CHT, IAT and CKP inputs to initiate Secondary Air Injection function.
2. When the engine is started, the strategy will determine when to enable the electric AIR pump. The PCM signals the AIR relay and the AIR bypass solenoid, after a (5 to 15) second delay, to begin system operation. Once the catalyst is lit-off, the PCM then signals the AIR relay to stop AIR pump operation and to close the AIR bypass solenoid from supplying vacuum to the AIR diverter valve(s).
3. The AIR relay provides the start-up signal and will switch the high current required to operate the AIR pump.
4. The AIR bypass solenoid applies a vacuum to the AIR diverter valve(s) causing it to open and to allow air to flow into the exhaust manifolds.
5. The function of the water shield if equipped is to provide the AIR pump with a source of dry air.
6. The electric AIR pump delivers the required amount of air to control emissions during engine operation. Air is forced into the exhaust manifolds to oxidize the hydrocarbons and carbon monoxide created by running rich at start up.

Scheme 297

Electric AIR Pump

The electric AIR pump (Scheme 298) provides pressurized air to the Secondary Air Injection system. The electric AIR pump functions independently of rpm and is controlled by the PCM. The electric AIR pump is only used for short periods of time. Delivery of air is dependent on the amount of system backpressure and system voltage. The inlet system of the AIR pump incorporates a splash cap which helps to guard against dirt and water.

Scheme 298

AIR Bypass Solenoid

The secondary air injection bypass (AIR bypass) solenoid (Scheme 299) is used by the PCM to control vacuum to the secondary air injection diverter (AIR diverter) valve. The AIR bypass solenoid is a normally closed solenoid. The AIR bypass solenoid also has a filtered vent feature to permit vacuum release.

Scheme 299

AIR Diverter Valve

The secondary air injection diverter (AIR diverter) valve (Scheme 300) is used with the electric AIR pump to provide on/off control of air to the exhaust manifold and catalytic converter. When the electric AIR pump is on and vacuum is supplied to the AIR diverter valve, air passes the integral check valve disk. When the electric AIR pump is off, and vacuum is removed from the AIR diverter valve, the integral check valve disk is held on the seat and stops air from being drawn into the exhaust system and prevents the back flow of the exhaust into the Secondary Air Injection System.

Scheme 300

Variable Cam Timing

The VCT (variable cam timing) system consists of an electric hydraulic positioning control solenoid, a CMP (camshaft position sensor) and trigger wheel. The CMP trigger wheel has a number of equally spaced teeth equal to the number (n) of cylinders on a bank plus one extra tooth (n+1). Four cylinder and V8 engines use a CMP 4+1 tooth trigger wheel. V6 engines use a CMP 3+1 tooth trigger wheel. The extra tooth placed between the equally spaced teeth represents the CMP signal for that bank. A CKP (crankshaft position sensor) provides the PCM with crankshaft positioning information in 10 degree increments (Scheme 301)

1. The PCM receives input signals from the IAT (intake air temperature), ECT (engine coolant temperature), EOT (engine oil temperature), CMP, TP (throttle position), MAF (mass air flow) and CKP to determine the operating conditions of the engine. At idle (low engine speeds and closed throttle) the PCM controls camshaft position based on air and coolant temperatures. During part and wide open throttle, camshaft position is determined by engine RPM, load and throttle position. The VCT system will not operate until the engine is at normal operating temperature.
2. The VCT system is enabled by the PCM when the proper conditions are met.
3. The CKP signal is used as a reference for CMP positioning.
4. The VCT solenoid valve is an integral part of the VCT system. The solenoid valve controls the flow of engine oil in the VCT actuator assembly. As the PCM controls the duty cycle of the solenoid valve, oil pressure/flow advances or retards the cam timing. Duty cycles near 0% or 100% represent rapid movement of the camshaft. Retaining a fixed camshaft position is accomplished by dithering (oscillating) the solenoid valve duty cycle. The PCM calculates and determines the desired camshaft position. It will continually update the VCT solenoid duty cycle until desired positioning is achieved. A difference between the desired and actual camshaft position represents a position error in the PCM's VCT control loop. The PCM will disable the VCT and place the camshaft in a default position if a fault is detected. A related DTC will also be set when this fault is detected.
5. When the VCT solenoid is energized, engine oil is allowed to flow to the VCT actuator assembly which advances or retards the cam timing. One half of the VCT actuator is coupled to the camshaft and the other half is connected to the timing chain. Oil chambers between the two halves couple the camshaft to the timing chain. When the flow of oil is shifted from one side of the chamber to the other, the differential change in oil pressure forces the camshaft to rotate in either a advance or retard position depending on the oil flow.

Scheme 301

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 concentration of exhaust gas products released to the atmosphere must be controlled. The catalytic converter assists in this task. It contains a catalyst in the form of a specially treated ceramic honeycomb structure saturated with catalytically active precious metals. As the 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.

Light Off Catalyst

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

Three-Way Catalyst (TWC) Conversion Efficiency

A TWC requires a stoichiometric fuel ratio, 14.7 pounds of air to 1 pound of fuel (14.7:1), for high conversion efficiency. In order to achieve these high efficiencies, the air/fuel ratio must be tightly controlled with a narrow window of stoichiometry. Deviations outside of this window will greatly decrease the conversion efficiency (Scheme 302) For example a rich mixture will decrease the HC and CO conversion efficiency while a lean mixture will decreases the NO x conversion efficiency.

Scheme 302

Exhaust System

The purpose of the exhaust system is to convey engine emissions from the exhaust manifold to the atmosphere. Engine exhaust emissions are directed from the engine exhaust manifold to the catalytic converter through the front exhaust pipe. An HO2S is mounted on the front exhaust pipe before the catalyst. The catalytic converter reduces the concentration of carbon monoxide (CO), unburned hydrocarbons (HCs) and oxides of nitrogen (NO x ) in the exhaust emissions to an acceptable level. The reduced exhaust emissions are directed from the catalytic converter through another HO2S mounted in the rear exhaust pipe (Scheme 303) and then on into the muffler. Lastly, the exhaust emissions are directed to the atmosphere through an exhaust tailpipe.

Note on some Partial Zero Emission Vehicles (PZEV), there will be a total of 3 HO2S in the exhaust stream. One near the exhaust manifold (stream 1), one in the middle of the light-off catalyst (stream 2) and the third (stream 3) is mounted after the light-off catalyst (Scheme 304)

Scheme 303

Scheme 304

Underbody Catalyst

The underbody catalyst is located after the light off catalyst. The underbody catalyst may be in-line with the light off catalyst, or the underbody catalyst may be common to two light off catalysts, forming a "Y" pipe configuration. For an exact configuration of the catalyst and exhaust system for a specific vehicle, refer to the appropriate EXHAUST SYSTEM article for that vehicle.

Three-Way Catalytic Converter

The three-way catalytic (TWC) converter contains either platinum (Pt) and rhodium (Rh) or palladium (Pd) and rhodium (Rh). The TWC converter catalyzes the oxidation reactions of unburned HCs and CO and the reduction reaction of NO x . The three-way conversion can be best accomplished by always operating the engine air fuel/ratio at or close to stoichiometry.

Exhaust Manifold/Runners

The exhaust manifold runners collect exhaust gases from engine cylinders. The number of exhaust manifolds and exhaust manifold runners depends on the 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 the flow of exhaust gases from the engine exhaust manifold through the catalytic converter and the muffler.

Heated Oxygen Sensors (HO2S)

The HO2S provide the powertrain control module (PCM) with voltage and frequency information related to the oxygen content of the exhaust gas. (Refer to the PCM INPUTS for a description of how the HO2S operates.)

Muffler

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

Supercharger Bypass System

The Supercharger Bypass (SCB) System allows the high pressure air at the outlet of the supercharger to vent back in the inlet of the supercharger, equalizing the pressure. This eliminates the boost (increased pressure that a supercharger produces) for times when supercharger function is undesirable. The components in this system are the vacuum bypass actuator see scheme 133 (which controls the bypass valve inside the supercharger), a supercharger (boost) bypass (SCB) solenoid see scheme 134 and a vacuum reservoir see scheme 135 The system normally operates with engine vacuum applied to the upper port of the vacuum bypass actuator, while the lower port references the air pressure in the clean air tube to cancel out any pressure difference in the intake air system. The actuator is set to open (bypassing the supercharger) during high vacuum engine conditions. As the throttle is opened, and engine vacuum decreases, the actuator closes to allow the supercharger to pressurize the air in the manifold. If an undesirable condition occurs in the engine, such as overheating or a critical Electric Engine Control (Electronic EC) sensor failure, the powertrain control module (PCM) also has the ability to control the SCB solenoid and direct the vacuum bypass actuator to bypass the supercharger. Once the engine condition has been corrected, the PCM allows the engine vacuum to control the vacuum bypass actuator.

Intercooler System

The Intercooler System (Scheme 305) and (Scheme 306) is designed to cool the induction air, which has been heated by the supercharger. The removal of heat from the pressurized air going into the intercooler increases the air density, which improves combustion efficiency, engine horsepower and torque. The system consists of an additional radiator in the grille, a reservoir (independent from engine cooling system), an electric water pump, a heat exchanger (intercooler) located in the lower intake manifold and tubing to interconnect these components. The intercooler is positioned after the supercharger, directly in the flow of the intake air. As the heated air flows through the intercooler, heat is transferred to the coolant which is circulated back to the intercooler radiator to be cooled by the airflow through the grille. The intercooler pump is controlled by the powertrain control module (PCM) to maintain a desirable intake air temperature by a second intake air temperature (IAT2) sensor in the lower intake manifold.

Scheme 305

Scheme 306

Electronic Throttle Body (ETB)

The Gen II electronic throttle body (Scheme 307) has the following characteristics

1. The DC motor is driven by the PCM (requires two wires). The gear ratio from the motor to the throttle plate shaft is 17:1.
2. There are two designs; parallel and in-series. The parallel design has the motor under the bore parallel to the plate shaft. The motor housing is integrated into the main housing (in general this is more difficult to package). The in-series design has a separate motor housing that protrudes out and offers more packaging flexibility.
3. Two springs are used: one is used to close the throttle (main spring) and the other is in a plunger assembly that results in a default angle with no power applied. This is for limp home reasons (force of plunger spring is 2 times stronger than the main spring). Default angle is usually set to result in a top vehicle speed of 30 MPH (48Km). Typically this throttle angle is 7 to 8 degrees from the hard-stop angle.
4. The closed throttle plate hard stop is used to avoid the throttle from binding in the bore (~0.75 degree). This hard stop setting is non-adjustable and is set to result in less airflow than the minimum engine airflow required at idle.
5. Unlike cable type throttle bodies, the intent for the ETB is not to have a hole in the throttle plate or to use plate sealant. The hole is not required in the ETB because the required idle airflow is provided by the plate angle in the throttle body assembly. This plate angle controls idle and idle quality and eliminates the need for IAC bypass actuator.
6. The system has two throttle position sensors. Redundant throttle position signals are required for monitor reasons. TP1 has a negative slope (increasing angle, decreasing voltage) and TP2 has a positive slope (increasing angle, increasing voltage). During normal operation the negative sloped TP sensor (TP1) is used by the control strategy as the indication of throttle position. The TP sensor assembly requires four wires.

1. 5 V Reference Voltage
2. Signal Return (ground)
3. TP1 voltage with negative voltage slope (5-0)
4. TP2 voltage with positive voltage slope (0-5)

Accelerator Pedal Position Sensors (APPS)

The ETC strategy uses pedal position sensors as an input to determine the driver demand.

1. There are three pedal position sensors required for system monitoring. APP1 has a negative slope (increasing angle, decreasing voltage) and APP2 & APP3 both have a positive slope (increasing angle, increasing voltage). During normal operation APP1 is used as the indication of pedal position by the strategy.
2. There are two VREF wires, two signal return wires and three signal wires (total of seven wires and pins) between the PCM and APPS assembly. 2- 5 V Reference Voltage 2- Signal Return (ground) APP1 voltage with negative voltage slope (5-0) APP2 voltage with positive voltage slope (0-5) APP3 voltage with positive voltage slope (0-5)
3. The pedal position signal is converted to pedal travel degrees (rotary angle) by the PCM. The software then converts these degrees to counts, which is the input to the torque based strategy.
4. The three pedal position signals ensure a correct input to the PCM, if any one signal has a fault. The PCM knows if a signal is wrong by calculating where it should be, inferred by the other signals. A value will be substituted for a faulty signal if two out of the three signals are bad.

Scheme 307

Electronic Throttle Control System Strategy

As stated earlier the torque based ETC strategy was developed mainly to improve fuel economy and to accommodate Variable Cam Timing. This is possible by not coupling the throttle angle to the drivers pedal position. By uncoupling the throttle angle (produce engine torque) from pedal position (driver demand). This allows the powertrain control strategy to optimize fuel control and transmission shift schedules while delivering the requested wheel torque. ETC is used on the 2004 MY Lincoln LS and Ford Thunderbird, Explorer/Mountaineer, and the new light-duty F-series.

The ETC monitor system is distributed across two processors within the PCM: the main powertrain control processor unit (CPU) and a monitoring processor called an Enhanced-Quizzer (E-Quizzer) processor. The primary monitoring function is performed by the Independent Plausibility Check (IPC) software, which resides on the main processor. It is responsible for determining the driver-demanded torque and comparing it to an estimate of the actual torque delivered. If the generated torque exceeds driver demand by specified amount, the IPC takes appropriate mitigating action.

Scheme 308

Since the IPC and main controller share the same processor, they are subject to a number of potential, common failure modes. Therefore, the E-Quizzer processor was added to redundantly monitor selected PCM inputs and to act as an intelligent watchdog and monitor the performance of the IPC and the main processor. If it determines that the IPC function is impaired in any way, it takes appropriate Failure Mode and Effects Management (FMEM) actions.

ETC SYSTEM FAILURE MODE AND EFFECTS MANAGEMENT

ELECTRONIC THROTTLE MONITOR OPERATION

Accelerator and Throttle Position Sensor Inputs

ACCELERATOR PEDAL POSITION SENSOR CHECK

THROTTLE POSITION SENSOR CHECK

Throttle Plate Position Controller (TPPC) Outputs

The purpose of the TPPC is to control the throttle position to the desired throttle angle. It is a separate chip embedded in the PCM. The desired angle is communicated from the main CPU via a 312.5 Hz duty cycle signal. The TPPC interprets the duty cycle signal as follows

1. 0% <= DC < 5% - Out of range, limp home default position.
2. 5% <= DC < 6% - Commanded default position, closed.
3. 6% <= DC < 7% - Commanded default position. Used for key-on, engine off.
4. 7% <= DC < 10% - Closed against hard-stop. Used to learn zero throttle angle position (hard-stop) after key-up.
5. 10% <= DC <=92% - Normal operation, between 0 degrees (hard-stop) and 82%, 10% duty cycle = 0 degrees throttle angle, 92% duty cycle = 82 degrees throttle angle.
6. 92% < DC <= 96% - Wide Open Throttle, 82 to 86 degrees throttle angle.
7. 96% < DC <= 100% - Out of Range, limp home default position.

The desired angle is relative to the hard-stop angle. The hard-stop angle is learned during each key-up process before the main CPU requests the throttle plate to be closed against the hard-stop. The output of the TPPC is a voltage request to the H-driver (also in PCM). The "H" driver is capable of positive or negative voltage to the Electronic Throttle Body Motor.

THROTTLE PLATE CONTROLLER CHECK OPERATION