Part 2
ENGINE CONTROL COMPONENTSNOTE: Transmission inputs, which are not described are discussed in the applicable Vehicle System transmission section.
Fan Control
The PCM monitors certain parameters (such as engine coolant temperature, vehicle speed, A/C on/off status, A/C pressure) to determine engine cooling fan needs.
For variable speed electric fan(s):
Edge/MKX, Five Hundred/Freestyle/Montego, Fusion/Milan/MKZ, Crown Victoria/Grand Marquis, Town Car: FCV Duty Cycle Output From PCM (Negative Duty Cycle):
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).
For relay controlled fans:
2.0L Focus (with A/C) And Taurus: PCM FC Output State For Cooling Fan Speeds:
2.3L Escape: PCM FC Output State For Cooling Fan Speeds:
Freestar, Monterey: PCM FC Output State For Cooling Fan Speeds:
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. Some applications will have the xFC circuit wired to 2 separate relays.
For 3-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 table.
Fan Speed Sensor (FSS)
Cooling Fan Clutch With (FSS):
The FSS is a Hall-effect sensor that measures the cooling fan clutch speed by generating a waveform with a frequency proportional to the fan speed. If the cooling fan clutch is moving at a relatively low speed, the sensor produces a signal with a low frequency. As the cooling fan clutch speed increases, the sensor generates a signal with a higher frequency. The powertrain control module (PCM) uses the frequency signal generated by the FSS as a feedback for closed loop control of the cooling fan clutch.
Fuel Injectors
Typical Fuel Injector:
CAUTION: Do not apply battery positive voltage (B+) directly to the fuel injector electrical connector terminals. The solenoids may be damaged internally in a matter of seconds.
The fuel injector 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 a 12-volt source from either the electronic engine control (EEC) power relay or fuel pump relay. The ground signal is controlled by the PCM.
The injector is the deposit resistant injector (DRI) type and does not have to be cleaned. However, it can be flow checked and, if found outside of specification, a new fuel injector should be installed.
Fuel Level Input (FLI)
The FLI is a communications network message. Most vehicle applications use a potentiometer type FLI sensor connected to a float in the FP module to determine fuel level.
Fuel Pump (FP) Module
Typical Electronic Returnless Fuel Pump (FP) Module:
Typical Mechanical Returnless Fuel Pump (FP) Module:
The FP module 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.
Fuel Pump (FP) Module and Reservoir
The FP module is mounted inside the fuel tank in a reservoir. The pump has a discharge check valve that maintains the system pressure after the key has been turned off to minimize starting concerns. The reservoir prevents fuel flow interruptions during extreme vehicle maneuvers with low tank fill levels.
Fuel Rail Pressure (FRP) Sensor
Fuel Rail Pressure (FRP) Sensor:
The FRP sensor is a diaphragm strain gauge device in which resistance changes with pressure. The electrical resistance of a strain gauge increases as pressure increases, and the resistance decreases as the 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.
Fuel Rail Pressure Temperature (FRPT) Sensor
Typical Fuel Rail Pressure Temperature (FRPT) Sensor:
The FRPT sensor measures the pressure and temperature of the fuel in the fuel rail and sends these signals to the PCM. The sensor uses the intake manifold vacuum as a reference to determine the pressure difference between the fuel rail and the intake manifold. The relationship between fuel pressure and fuel temperature is used to determine the possible presence of fuel vapor in the fuel rail.
The temperature sensing portion of the FRPT sensor is a thermistor device in which resistance changes with temperature. The electrical resistance of the thermistor decreases as the temperature increases, and the resistance increases as the temperature decreases. The varying resistance changes the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature.
Both the pressure and temperature signals are used to control the speed of the fuel pump. The speed of the fuel pump sustains fuel rail pressure which preserves 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.
Fuel Rail Pulse Damper
Typical Fuel Rail Pulse Damper:
The fuel rail pulse damper is located on the fuel rail and reduces the 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 if the pulse damper diaphragm ruptures. The fuel rail pulse damper should not be confused with a fuel pressure regulator; it does not regulate the fuel rail pressure.
Fuel Tank Pressure (FTP) Sensor
Fuel Tank Pressure (FTP) Sensor:
In-Line Fuel Tank Pressure (FTP) Sensor:
The FTP sensor or in-line FTP sensor is used to measure the fuel tank pressure.
Heated Oxygen Sensor (HO2S)
Heated Oxygen Sensor (HO2S):
The HO2S 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 a temperature of 800°C (1,472°F). At approximately 300°C (572°F) the engine can enter closed loop operation. The VPWR circuit supplies voltage to the heater. The PCM turns the heater on by providing the ground when the correct conditions occur. The heater allows the engine to enter closed loop operation sooner. The use of this heater requires the HO2S heater control to be duty cycled, to prevent damage to the heater.
Idle Air Control (IAC) Valve
NOTE: The IAC valve assembly is not adjustable and cannot be cleaned, also some IAC valves are normally open and others are normally closed. Some IAC valves require engine vacuum to operate.
The IAC valve assembly controls the 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.
The PCM uses the IAC valve assembly to control:
- no touch start
- cold engine fast idle for rapid warm-up
- idle (corrects for engine load)
- stumble or stalling on deceleration (provides a dashpot function)
- over-temperature idle boost
Inertia Fuel Shutoff (IFS) Switch
Typical Inertia Fuel Shutoff (IFS) Switch:
The IFS switch is used in conjunction with the electric fuel pump. The purpose of the IFS switch is to shutoff 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's Literature for the location of the IFS.
Intake Air Temperature (IAT) Sensor
Typical Stand-Alone/Non-Integrated Intake Air Temperature (IAT) Sensors:
Typical Integrated Intake Air Temperature (IAT) Sensor Incorporated Into A Drop-in Or Flange-type MAF Sensor:
The IAT sensor is a thermistor device in which resistance changes with temperature. The electrical resistance of a thermistor decreases as the temperature increases, and the resistance 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 2 design types of IAT sensors used, a stand-alone/non-integrated type and a integrated 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. One is located before the supercharger at the air cleaner for standard OBD/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 spark and to help determine charge air cooler (CAC) efficiency.
Intake Manifold Tuning Valve (IMTV)
WARNING: Substantial opening and closing torque is applied by this system. To prevent injury, be careful to keep fingers away from lever mechanisms when actuated.
The IMTV 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 is not energized below approximately 2,600 RPM. The shutter is in the closed position not allowing airflow blend to occur in the intake manifold. The motorized unit is energized above approximately 2,600 RPM. The motorized unit is 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.
Knock Sensor (KS)
Two Types Of Knock Sensor (KS):
The KS 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.
Manifold Absolute Pressure (MAP) Sensor
Typical Manifold Absolute Pressure (MAP) Sensor:
The MAP sensor measures intake manifold absolute pressure. The PCM uses information from the MAP sensor to measure how much exhaust gas is introduced into the intake manifold.
Mass Air Flow (MAF) Sensor
Diagram Of Air Flow Through Throttle Body Contacting MAF Sensor Hot And Cold Wire (and IAT Sensor Wire Where Applicable) Terminals:
Typical Mass Air Flow (MAF) Sensor:
Typical Drop-in Mass Air Flow (MAF) Sensor:
The 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 the ambient temperature as measured by a constant cold wire. The current required to maintain the temperature of the hot wire is proportional to the mass air 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.
The MAF sensor is located between the air cleaner and the throttle body or inside the air cleaner assembly. Most MAF sensors have integrated bypass technology with an integrated intake air temperature (IAT) sensor. The hot wire electronic sensing element must be replaced as an assembly. Replacing only the element may change the air flow calibration.
Output Shaft Speed (OSS) Sensor
The OSS sensor provides the 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 that is generated.
Power Steering Pressure (PSP) Sensor
Typical Power Steering Pressure (PSP) Sensor:
The PSP sensor monitors the hydraulic pressure within the power steering system. The PSP sensor voltage input to the PCM changes 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 the transmission electronic pressure control (EPC) pressure during increased engine load, for example, during parking maneuvers.
Power Steering Pressure (PSP) Switch
Typical Power Steering Pressure (PSP) Switch:
The PSP switch 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 provides a low current voltage on the PSP circuit. When the PSP switch is closed, this voltage is pulled low through the SIG RTN circuit. 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 the transmission electronic pressure control (EPC) pressure during increased engine load, for example during parking maneuvers.
Power Take-Off (PTO) Switch and Circuits
The PTO circuit is used by the PCM to disable some of the on board diagnostics (OBD) 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. The PTO indicator lamp illuminates when the PTO system is functioning correctly and flashes when the PTO system is damaged
When the PTO unit is activated, the PCM disables some OBD monitors, which may not function reliably during PTO operation. Without the PTO circuit information to the PCM, false DTCs may be set during PTO operation. Prior to an Inspection/Maintenance test, operate the vehicle with the PTO disengaged long enough to successfully complete the OBD Monitors.
PTO Circuits Description
The 3 PTO input circuits are PTO mode, PTO engage, and PTO RPM.
The PTO engage circuit is used when the operator is requesting the PCM to check the needed inputs required to initiate the PTO engagement.
The PTO RPM circuit is used for the operator to request additional engine RPM for PTO operation.
Powertrain Control Module - Vehicle Speed Output (PCM-VSO)
The PCM-VSO 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 hardwired signal or as a message on the vehicle communication network.
The key features of the PCM-VSO system are to:
- infer vehicle movement from the output shaft speed (OSS) sensor signal.
- convert transmission output shaft rotational information to vehicle speed information.
- compensate for tire size and axle ratio with a programmed calibration variable.
- use a transfer case speed sensor (TCSS) for four wheel drive (4WD) applications.
- distribute vehicle speed information as a multiplexed message and/or an analog signal.
The signal from a non-contact shaft sensor OSS or TCSS mounted on the transmission (automatic, manual, or 4WD transfer case) is sensed directly by the PCM. The PCM converts the 0SS or TCSS information to 8,000 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 hardwired interface between the vehicle speed signal user and the PCM, or by a speed and odometer data message through the vehicle communication network data link.
The PCM-VSO hardwired signal wave form is a DC square wave with a voltage level of 0 to VBAT. Typical output operating range is 1.3808 Hz per 1 km/h (2.22 Hz per mph).
Secondary Air Injection (AIR) Bypass Solenoid
Secondary AIR Bypass Solenoid:
The secondary AIR bypass solenoid is used by the PCM to control vacuum to the secondary air injection diverter (AIR diverter) valve. The secondary AIR bypass solenoid is a normally closed solenoid. The secondary AIR bypass solenoid also has a filtered vent feature to permit vacuum release.
Secondary AIR Diverter Valve
Secondary AIR Diverter Valve:
The secondary AIR diverter valve is used with the secondary AIR pump to provide on/off control of air to the exhaust manifold and catalytic converter. When the secondary AIR pump is on and vacuum is supplied to the AIR diverter valve, air passes the integral check valve disk. When the secondary 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 system.
Secondary AIR Pump
Secondary Air Pump:
The secondary AIR pump provides pressurized air to the secondary AIR system. The secondary AIR pump functions independently of RPM and is controlled by the PCM. The secondary 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 secondary AIR pump draws dry filtered air from the intake air system downstream of the MAF/IAT sensor.
Starter Motor Request (SMR) Circuit
The SMR circuit provides the PCM with a signal from the ignition switch to the PCM. The input is pulled high when the key is in the START position and the transmission range sensor ignition lockout circuit allows the starter to engage.
Throttle Position (TP) Sensor
Typical TP Sensor:
The TP sensor 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 3-blade electrical connector that may be gold plated. The gold plating increases the corrosion resistance on the terminals and increases the connector durability. The TP sensor is mounted on the throttle body. As the TP sensor is rotated by the throttle shaft, 4 operating conditions are determined by the PCM from the TP. The operating 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)
- throttle angle rate
Transmission Control Indicator Lamp (TCIL)
The TCIL is an output signal from the PCM that controls the lamp on/off function depending on the engagement or disengagement of overdrive.
Transmission Control Switch (TCS)
Typical Transmission Control Switch (TCS):
Typical Transmission Control Switch (TCS):
The TCS signals the PCM with VPWR whenever the TCS is pressed. On vehicles with this feature, the transmission control indicator lamp (TCIL) illuminates when the TCS is cycled to disengage overdrive.
Vapor Management Valve (VMV)
See the description of the EVAP canister purge valve.
Vehicle Speed Sensor (VSS)
Typical Vehicle Speed Sensor (VSS):
The VSS 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.