NOTE: Transmission input, which are not described here are discussed in the respective transmission system.
Air Conditioning Cycling Switch
The Air Conditioning (A/C) cycling switch may be wired to either the A/C Cycling Switch (ACCS) or ACPSW Powertrain Control Module (PCM) input. When the A/C cycling switch opens, the PCM will turn off the Air Conditioning (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 Vehicle/Diagrams for vehicle specific wiring.
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 - Standard Corporate Protocol (SCP) communication.
A/C Pressure Sensor Output Voltage VS Pressure Chart
Typical Air Conditioning Pressure Sensor
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.
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 Vehicle/Diagrams.
Typical Brake Pedal Position Switch
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 stoplamp circuit, if all stoplamp 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 amp bulbs has failed.
Typical Hall-Effect Sensor
Typical Variable Reluctance Sensor
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 Clutch Pedal Position (CPP)/Park-Neutral Position (PNP) Switches
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 Vehicle Reference Voltage (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.
Three Different Types Of Crankshaft Position (CKP) Sensors
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).
Cylinder Head Temperature (CHT) Sensor
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. See: Description and Operation\Standard Models (Non BI-Fuel)\Powertrain Control Software
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.
Engine Fuel Temperature (EFT) 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 Oil Temperature (EOT) Sensor
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.
Flexible Fuel (FF) 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:
Frequency Table
All duty cycle frequency values are +1/-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 Heated Oxygen Sensor (HO2S) input signals.
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 Duty Cycle Signals, Part 1
Fuel Pump Driver Module Duty Cycle Signals, Part 2
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 table.
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.
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.
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 (HO2S)
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 Vehicle Power (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 is not interchangeable with new style 3.3 ohm heater.
Intake Air Temperature (IAT)
Diagram Of Air Flow Through Throttle Body Contacting MAF Sensor Hot and Cold Wire Terminals
Intake Air Temperature Sensor
The Intake Air Temperature (IAT) sensors (Figure 34) and integrated Mass Air Flow (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) AT sensors. Both sensors operate as above. However, one is located before the supercharger at the air cleaner for standard OBD II/cold weather input, while a second sensor Second Intake Air Temperature (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.
Intake Manifold Runner Control
For information on the Intake Manifold Runner Control (IMRC) , refer to Fuel Delivery and Air Induction.
Intake Manifold Swirl Control
For information on the Intake Manifold Swirl Control (IMSC) , refer to Fuel Delivery and Air Induction.
Intake Manifold Tuning Valve
For information on the Intake Manifold Tuning Valve (IMTV) , refer to Fuel Delivery and Air Induction.
Two Types Of Knock Sensor (KS)
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.
