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POWERTRAIN CONTROL MODULE (PCM) INPUTS
NOTE: Transmission inputs, which are not described are discussed in the respective transmission Vehicle Systems.
Accelerator Pedal Position (APP) Sensor
For information on the APP sensor, refer to the description for Torque Based Electronic Throttle Control (ETC).
Air Conditioning (A/C) Cycling Switch
The 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 Heating and Air Conditioning. Also, refer to the applicable Vehicle/Diagrams 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 (ACET) Sensor
The ACET sensor measures the 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 the resistance 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.
Air Conditioning (A/C) Pressure Sensor
A/C Pressure Sensor Output Voltage Vs. Pressure Chart:
Typical A/C Pressure Sensor:
The A/C pressure sensor is located in the high pressure (discharge) side of the A/C system. The A/C pressure sensor provides a voltage signal to the 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.
Air Conditioning (A/C) 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 multiple speed, relay controlled 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 results 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 then turns on the high speed fan to help reduce the pressure.
For additional information, refer to Heating and Air Conditioning or Vehicle/Diagrams.
Brake Pedal Position (BPP) Switch
Typical Brake Pedal Position (BPP) Switch:
The BPP switch 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:
- BPP switch is hard wired to the PCM supplying battery positive voltage (B+) when the vehicle brake pedal is applied.
- BPP switch is hard wired to a module (ABS, LCM, or REM), the BPP signal is then broadcast over the data link to be received by the PCM.
- BPP switch is hard wired to the anti-lock brake system (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 stop lamp circuit, if all stop lamp 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 stop lamp bulbs has failed.
Brake Pedal Switch (BPS)/Brake Deactivator Switch
The BPS, also sometimes called the brake deactivator switch, is for vehicle speed control deactivation. A normally closed switch supplies battery positive voltage (B+) to the PCM when the brake pedal is NOT applied. When the brake pedal is applied, the normally closed switch opens and power is removed from the PCM.
On some applications the normally closed BPS, 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 (CMP) Sensor
F-150 Hall-Effect CMP Sensor:
Typical Variable Reluctance CMP Sensor:
The 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 PCM and used for synchronizing the sequential firing of the fuel injectors. Coil-on-plug (COP) ignition applications 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 2 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 2 types of CMP sensors: the 3-pin connector Hall-effect type sensor (only used on F-150 4.2L applications) and the 2 pin connector variable reluctance type sensor used on all other vehicle applications.
Clutch Pedal Position (CPP) Switch
Typical Clutch Pedal Position (CPP) Switch:
The CPP switch is an input to the PCM indicating the clutch pedal position. The PCM provides a low current voltage on the CPP circuit. When the CPP switch is closed, this voltage is pulled low through the SIG RTN circuit. The CPP input to the PCM is used to detect a reduction in engine load. The PCM uses the load information for mass air flow and fuel calculations.
Crankshaft Position (CKP) Sensor
Three Different Types Of Crankshaft Position (CKP) Sensors:
The 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 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 10-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 PCM uses the CKP signal to synchronize the ignition system and track the rotation of the crankshaft.
Cylinder Head Temperature (CHT) Sensor
Typical Cylinder Head Temperature (CHT) Sensor:
The CHT sensor is a thermistor device in which resistance changes with temperature. The electrical resistance of a thermistor decreases as 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 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 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.
Differential Pressure Feedback EGR (DPFE) Sensor
For information on the DPFE sensor, refer to the description of the Exhaust Gas Recirculation Systems.
Electronic Throttle Body (ETB) Position Sensor
For information on the electronic throttle body position sensor, refer to the description of the ETB in Torque Based Electronic Throttle Control (ETC).
Engine Coolant Temperature (ECT) Sensor
Typical Engine Coolant Temperature (ECT) Sensor:
The ECT 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 ECT measures the temperature of the engine coolant. The sensor is threaded into an engine coolant passage.
Engine Oil Temperature (EOT) Sensor
Typical Engine Oil Temperature (EOT) Sensor:
The EOT 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 EOT sensor measures the temperature of the engine oil. The sensor is typically threaded into the engine oil lubrication system. The PCM can use the EOT sensor input to determine the following:
- On variable cam timing (VCT) applications the EOT input is used to adjust the VCT control gains and logic for camshaft timing.
- The PCM can use EOT sensor input in conjunction with other PCM inputs to determine oil degradation.
- 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.
Fuel Level Input
NOTE: The Ford GT will use a piezoelectric sonar type fuel level sensor. The sensor is located in the tank and the sensor signal is provided as a communications network message by the instrument cluster to the PCM.
The fuel level input (FLI) is either a hard wire signal input to the PCM from the fuel pump (FP) module or 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 Monitor (FPM)
Applications Using a Fuel Pump Relay for Fuel Pump On/Off Control
The FPM circuit is spliced into the fuel pump power (FP PWR) circuit and is used by the PCM for diagnostic purposes. The PCM sources a low current voltage down the FPM circuit. With the fuel pump off, this voltage is pulled low by the path to ground through the fuel pump. With the fuel pump off and the FPM circuit low, the PCM can verify that the FPM circuit and the FP PWR circuit are complete from the FPM splice through the fuel pump to ground. This also confirms that the FP PWR or FPM circuits are not shorted to power. With the fuel pump on, voltage is now being supplied from the fuel pump relay to the FP PWR and FPM circuits. With the fuel pump on and the FPM circuit high, the PCM can verify that the FP PWR circuit from the fuel pump relay to the FPM splice is complete. It can also verify that the fuel pump relay contacts are closed and there is a B+ supply to the fuel pump relay.
Fuel Pump Driver Module (FPDM) Applications
NOTE: The Ford GT uses 2 FPDMs to control fuel for the dual-injection fuel delivery system. The PCM will individually monitor both FPDMs through their FPM circuits.
The FPDM communicates diagnostic information to the PCM through the FPM circuit. This information is sent by the FPDM as a duty cycle signal. The 3 duty cycle signals that may be sent are listed in the table.
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
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 fuel return line to the fuel tank has been deleted in this type of fuel system. The relationship between fuel pressure and fuel temperature is used to determine the possible presence of fuel vapor in the fuel rail. Both 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 Temperature (FRT) Sensor
Fuel Rail Temperature (FRT) Sensor:
The FRT 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 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 FRT 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.
Fuel Tank Pressure (FTP) Sensor
For information on the FTP sensor, refer to the description of the Evaporative Emission Systems.
Generator Load Input (GENLI)
For information on the GENLI. refer to the description of the Powertrain Control Module (PCM) Controlled Charging System.