Fuel Rail Pressure Sensor
The fuel rail pressure (FRP) sensor (Figure 31) 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.
Fuel Rail Pressure (FRP) Sensor on the 4.6L NG Crown Victoria
The fuel rail pressure (FRP) sensor (Figure 32) 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.
Typical Fuel Rail Pressure Temperature (FRPT) Sensor
Fuel Rail Pressure (FRP) Sensor
Generator Monitor (Gen Mon)
For information on the generator monitor, refer to the description of the PCM/Controlled Charging System.
Generator Load
The Generator Load Input (GLI) circuit is used by the PCM to determine generator load on the engine. As generator load increases the PCM will adjust idle speed accordingly. This strategy helps reduce idle surges due to switching high current loads. The GLI signal is sent to the PCM from the voltage regulator/generator. The signal is a variable frequency duty cycle. Normal operating frequency is 40 - 250 Hz. Normal signal DC voltage (referenced to ground) is between 1.5 V (low generator load) and 10.5 V (high generator load).
Heated Oxygen Sensor
The heated oxygen sensor (HO2S) (Figure 33) 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 low voltage signal less than 0.4 volt. A low concentration of oxygen (rich air/fuel ratio) produces a high 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 complete the ground when the proper conditions occur. For model year 1998 a new HO2S heater and heater control system are installed on some vehicles. The high power heater reaches closed loop fuel control temperatures. The use of this heater requires that the HO2S heater control be duty cycled, to prevent damage to the heater. The 6 ohm design isnot interchangeable with new style 3.3 ohm heater.
Town Car and Crown Victoria/Grand Marquis
Heated Oxygen Sensor (HO2S)
Intake Air Temperature Sensor
The intake air temperature (IAT) sensors (Figure 34) and integrated MAF type (Figure 37), are thermistor devices 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 MAF.
The IAT sensor provides a quicker temperature change response time than the ECT or CHT sensor.
Supercharged 5.4L Lightning vehicles use (2) IAT sensors. Both sensors 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.
Typical Stand-Alone/Non-Integrated Intake Air Temperature (IAT) Sensors
Intake Air Temperature (IAT)
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) (Figure 35) 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.
Two Types of Knock Sensor (KS)
Two Types of Knock Sensor (KS)
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 (Figure 36). 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.
Typical Mass Air Flow (MAF) Sensor
Typical Mass Air Flow (MAF) Sensor
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 (Figure 37). This input is also used in determining transmission electronic pressure control (EPC), shift and torque converter clutch scheduling.
Some MAF sensors have integrated bypass technology (IBT) with an integrated intake air temperature (IAT) sensor. The present applications with IBT are: Focus, Escort (4V), 2.0L Cougar, Escape, Taurus/Sable, Windstar, Explorer/Mountaineer and E-Series.
Diagram of Air Flow Through Throttle Body Contacting MAF Sensor Hot and Cold Wire (and IAT Sensor Wire Where Applicable) Terminals
Diagram of Air Flow through Throttle Body contacting MAF sensor hot and cold wire (and IAT sensor wire where applicable) terminals.
The MAF sensor is located between the air cleaner and the throttle body or inside the air cleaner assembly.
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 (Figure 38) 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.
Typical Power Steering Pressure (PSP) Switch
Power Steering Pressure (PSP) Switch
Power Steering Pressure Sensor
The power steering pressure (PSP) sensor (Figure 39) 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.
Typical Power Steering Pressure (PSP) Sensor
Power Steering Pressure (PSP) Sensor
Power Take-Off Switch and Circuit
The Power Take-Off (PTO) circuit (Figure 40) is used by the PCM to disable some of the OBD II Monitors during PTO operation. The PTO circuit normally carries low voltage. When the PTO switch is on/closed, B+ is supplied to the PTO input circuit indicating to the PCM that an additional load is being applied to the engine. If this action was not reported by the PTO circuit, a false Diagnostic Trouble Code may be stored.
Power Take-Off (PTO) Switch and Circuit to PCM
Purge Flow Sensor
For information on the purge flow (PF) sensor, refer to the description of the Evaporative Emission Systems.
Thermal Manifold Absolute Pressure Sensor
The Thermal Manifold Absolute Pressure Sensor (TMAP) (Figure 41)consists of a manifold absolute pressure (MAP) sensor and an integrated thermistor. The thermistor part of the sensor is currently not being used. The MAP part of the sensor measures intake manifold air absolute pressure. The PCM uses information from the MAP sensor, throttle position (TP) sensor, mass air flow (MAF) sensor, engine coolant temperature (ECT) or cylinder head temperature (CHT) sensor and crankshaft position (CKP) sensor to determine how much exhaust gas is introduced into the intake manifold.
Typical Manifold Absolute Pressure (MAP) Sensor
Thermal Manifold Absolute Pressure (TMAP) Sensor
Throttle Position Sensor
The throttle position (TP) sensor (Figure 42) 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.
Typical Throttle Position (TP) Sensor
Transmission Control Switch
The transmission control switch (TCS) (Figures 43 and 44) signals the PCM with keypower 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.
Typical Transmission Control Switch (TCS) (Column Shift)
Transmission Control Switch (TCS)
Transmission Control Switch (TCS)
Solid State Relay
For information on the solid state relay, refer to the description of the Secondary Air Injection Systems.
Vehicle Speed Sensor
The vehicle speed sensor (VSS) (Figure 45) 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.
Typical Vehicle Speed Sensor (VSS)
4x4 Mode Switch
The generic electronic module (GEM) 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 (Figure 44).
