PCM Inputs Note: Transmission input, which are not described are discussed in the respective transmission diagnostic/repair information.
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 Heating and Air Conditioning.
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 applicable Wiring 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 BUS + and BUS - (SCP) communication.
Air Conditioning Pressure Sensor
The air conditioning pressure (A/C pressure) sensor (Figure 20)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.
Typical ACP Transducer Sensor
Typical Air Conditioning Pressure Sensor
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 Heating and Air Conditioning or the Wiring Diagrams.
Brake Pedal Position Switch
The brake pedal position (BPP) switch (Figure 21) 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. On most applications the BPP switch is hard wired to the PCM and supplies battery positive voltage (B+) when the vehicle brake pedal is applied. On other applications the BPP switch signal is broadcast over the SCP link via another module to be received by the PCM.
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 Position Switch
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 firing of sequential 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.
There are two types of CMP sensors: the three pin connector Hall-effect type sensor (Figure 22) and the two pin connector variable reluctance sensor (Figure 23).
Typical Hall-Effect Sensor
Typical Variable Reluctance CMP Sensor
Typical Variable Reluctance Sensor
Clutch Pedal Position Switch
The clutch pedal position (CPP) switch (Figure 24) is an input to the PCM indicating the clutch pedal position and, in some manual transmission applications, both the clutch pedal engagement position and the gear shift position. The PCM provides a 5-volt reference (VREF) signal to the CPP switch and/or a park/neutral position (PNP) switch (on the CPP signal line). If the CPP switch (either or both CPP and PNP switches are closed) is closed, indicating the clutch pedal is engaged and the shift lever is in the NEUTRAL position, 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 (or PNP switch on vehicle or both CPP and PNP switches open on the vehicle) is open, meaning the clutch pedal is disengaged (all systems) and the shift lever is not in NEUTRAL position (PNP switch systems), 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.
Clutch Pedal Position (CPP) Switch
Crankshaft Position Sensor (Integrated Ignition Systems)
The crankshaft position (CKP) sensor 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 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 (Figure 25).
Three Different Types of Crankshaft Position (CKP) Sensors
Cylinder Head Temperature Sensor
The cylinder head temperature (CHT) sensor (Figure 26) 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.
Typical CHT Sensor
Cylinder Head Temperature (CHT) Sensor
Differential Pressure Feedback EGR Sensor
For information on the differential pressure feedback EGR sensor, refer to the description of the Exhaust Gas Recirculation Systems.
Engine Coolant Temperature
The engine coolant temperature (ECT) sensor (Figure 27) 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.
Typical Thread Type Sensor
Engine Coolant Temperature (ECT) Sensor Engine Fuel Temperature Sensor
The engine fuel temperature (EFT) sensor (Figure 28) 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.
Engine Fuel Temperature (EFT) Sensor used on the 4.6L NG Crown Victoria
Engine Oil Temperature
The engine oil temperature (EOT) sensor (Figure 29) 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 measures the temperature of the engine oil. The EOT sensor is similar in construction to the engine coolant temperature (ECT) sensor. On some applications, EOT input to the PCM is used to initiate a soft engine shutdown. This prevents engine damage from occurring as a result of high oil temperature.
Typical Thread Type Sensor
Engine Oil Temperature (EOT) Sensor Flexible Fuel Sensor
The flexible fuel (FF) sensor (Figure 30) is a capacitive device that detects the dielectric constant, conductivity and temperature of the fuel being fed to the engine. From this information, the FF sensor generates a duty cycle frequency that it supplies to the PCM telling it the percentage of ethanol in the fuel.
In general, as the percentage of ethanol in the fuel mixture increases, the output frequency of the FF sensor signal increases. The relationship between ethanol alcohol percentage and duty cycle frequency is as follows:
All duty cycle frequency values are +/-5%. It is important to note that currently no fuel with greater than 85% ethanol alcohol content is being produced. The PCM uses the percent ethanol information to calculate the correct A/F (air/fuel) ratio and spark advance for the vehicle.
Beginning in the 2001 model year, not all vehicles are equipped with flexible fuel sensors. On vehicles without flexible fuel sensors, the PCM calculates the A/F ratio based upon HO2S input signals.
Flexible Fuel (FF) Sensor
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 II Monitors.
Fuel Pump Monitor
Applications Using a Fuel Pump Relay for Fuel Pump On/Off Control
The Fuel Pump Monitor (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 Applications
The fuel pump driver module (FPDM) communicates diagnostic information to the powertrain control module (PCM) through the Fuel Pump Monitor (FPM) circuit. This information is sent by the FPDM as a duty cycle signal. The three duty cycle signals that may be sent are listed in the following table.
FUEL PUMP DRIVER MODULE DUTY CYCLE SIGNALS
a If a duty cycle meter and breakout box is used, be aware that these values may be reversed depending on the trigger setting of the specific meter (for example, 25% from FPDM may read as 75% on duty cycle meter depending on trigger setting).
b Value will fluctuate randomly. It is ok for value to briefly go outside this range, then return.
Fuel Tank Pressure Sensor
For information on the fuel tank pressure (FTP) sensor, refer to the description of the Evaporative Emission Systems.
