A - K

PCM INPUTS

NOTE: Transmission input, which are not described here are discussed in the respective transmission Vehicle Systems.

Air Conditioning Cycling Switch
The Air Conditioning (A/C) cycling switch may be wired to either the A/C Cycling Switch (ACCS) or Air Conditioning Pressure Switch (ACPSW) Powertrain Control Module (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 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 BUS + and BUS - (SCP) communication.

Air Conditioning Evaporator Temperature Sensor

A/C Evaporator Temperature (ACET) Sensor Voltage And Resistance Chart, Part 1:

A/C Evaporator Temperature (ACET) Sensor Voltage And Resistance Chart, Part 2:

The Air Conditioning Evaporative Temperature (ACET) sensor senses 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 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 Pressure Sensor

A/C Pressure Sensor Output Voltage VS Pressure Chart:

Typical Air Conditioning Pressure Sensor:

The Air Conditioning Pressure (A/C pressure) sensor (Figure 23) 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.

Brake Pedal Position Switch

Typical Brake Pedal Position Switch:

The Brake Pedal Position (BPP) switch (Figure 24) 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 is applied.
^ BPP switch is hard wired to a module (ABS, LCM or REM), BPP signal is then broadcasted over the data link to be received by the PCM.
^ BPP switch is hard wired to the anti-lock brake (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 then sent to the PCM and to other BPP signal users.

Note 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 stoplamp bulbs has failed.

Brake Pressure Applied/Brake Deactivator Switch
The Brake Pressure Applied (BPA) switch also sometimes called the brake deactivator switch for vehicle speed control deactivation. Is a normally closed switch, which supplies battery positive voltage (B+) to the PCM when the brake pedal is NOT applied. When the brake pedal is depressed, the normally closed switch will open and power is removed from the PCM.

On some applications the normally closed BPA switch 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 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.

Typical Hall-Effect Sensor:

Typical Variable Reluctant Sensor:

There are two types of CMP sensors: the three pin connector Hall-effect type sensor (Figure 25) and the two pin connector variable reluctance sensor (Figure 26).

Clutch Pedal Position Switch

Clutch Pedal Position (CPP) Switch:

The Clutch Pedal Position (CPP) switch (Figure 27) 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.

Crankshaft Position Sensor (Integrated Ignition Systems)

Crankshaft Position (CKP) Sensors:

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 28).

Cylinder Head Temperature Sensor

Cylinder Head Temperature (CHT) Sensor:

The Cylinder Head Temperature (CHT) sensor (Figure 29) 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.

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 Sensor

Engine Coolant Temperature (ECT) Sensor:

The Engine Coolant Temperature (ECT) sensor (Figure 30) 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 Intake Air Temperature (IAT) sensor.

Engine Fuel Temperature Sensor

Engine Fuel Temperature (EFT) Sensor:

The Engine Fuel Temperature (EFT) sensor (Figure 31) 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 Sensor

Engine Oil Temperature (EOT) Sensor:

The Engine Oil Temperature (EOT) sensor (Figure 32) 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 sensor measures the temperature of the engine oil. The sensor is typically threaded into the engine oil lubrication system near the oil filter. 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.

Fan Speed Sensor (FANSS)
For information on the Fan Speed Sensor (FANSS), refer to the description of the Visctronic Drive Fan (VDF) clutch.

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

Fuel Pump Driver Module Duty Cycle Signals, Part 1:

Fuel Pump Driver Module Duty Cycle Signals, Part 2:

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 Tank Pressure Sensor
For information on the Fuel Tank Pressure (FTP) sensor, refer to the description of the Evaporative Emission Systems.

Fuel Rail Pressure Sensor

Fuel Rail Pressure (FRP) Sensor:

The Fuel Rail Pressure (FRP) sensor (Figure 33) 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:

The fuel rail pressure (FRP) sensor (Figure 34) 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 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

Heated Oxygen Sensor (HO2S):

The Heated Oxygen Sensor (HO2S) (Figure 35) 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 voltage signal less than 0.4 volt. A low concentration of oxygen (rich air/fuel ratio) produces a 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 turn on the heater by providing the ground when the proper conditions occur. Since model year 1998 a high power HO2S heater and heater control system have been installed on the Stream 1 HO2S sensors of most vehicles. The high power heater reaches closed loop fuel control temperatures faster, which allows closed loop engine operation sooner. 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 Sensor

Intake Air Temperature (IAT) Sensors:

The intake air temperature (IAT) sensors (Figure 36) and integrated Mass Air Flow (MAF) type (Figure 39), 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 vehicles use (2) IAT sensors. Both sensors are thermistor type devices and 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.

Currently two types of IAT2 sensors are used. A non-integrated screw in type (Figure 36) and an integrated type, which is part of the Thermal Manifold Absolute Pressure (TMAP) sensor (Figure 43). The TMAP sensor consists of a IAT thermistor and a Manifold Absolute Pressure (MAP) sensor. The thermistor portion of the TMAP is used for IAT2 function and operates in the same manner as a non-integrated IAT2. For additional information on the MAP portion of the TMAP, refer to the Thermal Manifold Absolute Pressure Sensor description and operation.

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

Knock Sensor (KS):

The Knock Sensor (KS) (Figure 37) 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.