NOTE: Transmission input, which are not described here are discussed in the respective transmission system.
Typical Mass Air Flow (MAF) Sensor
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.
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.
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 (PSP) Switch
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.
Power Steering Pressure (PSP) Sensor
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.
Power Take-Off (PTO) Switch and Circuit To PCM
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.
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 (CKP) sensor and Crankshaft Position (CKP) sensor to determine how much exhaust gas is introduced into the intake manifold.
Typical Throttle Position (TP) 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.
Transmission Control Switch (TCS)
Transmission Control Switch (TCS)
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.
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 4x4 Switch
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 46).