Inputs
AIR CONDITIONING (A/C) CONTROLS-PCM INPUTThe A/C control system information applies to factory installed air conditioning units.
A/C SELECT SIGNAL: When the A/C switch is in the ON position, an input signal is sent to the Powertrain Control Module (PCM). The signal informs the PCM that the A/C has been selected. The PCM adjusts idle speed to a pre-programmed rpm through the Idle Air Control (IAC) motor to compensate for increased engine load.
A/C REQUEST SIGNAL: Once A/C has been selected, the powertrain control module (PCM) receives the A/C request signa]. from the clutch cycling pressure switch. The input indicates that the evaporator pressure is in the proper range for A/C application. The PCM uses this input to cycle the A/C compressor clutch (through the A/C relay). It will also determine the correct engine idle speed through the idle air control (IAC) motor position.
If the A/C low-pressure switch or high-pressure switch opens (indicating a low or high refrigerant pressure), the PCM will not receive an A/C request signal. The PCM will then remove the ground from the A/C relay. This will deactivate the A/C compressor clutch.
If the switch opens, (indicating that evaporator is not in proper pressure range), the PCM will not receive the A/C request signal. The PCM Will then remove the ground from the A/C relay, deactivating the A/C compressor clutch.
AUTOMATIC SHUTDOWN (ASD) RELAY SENSE-PCM INPUT
DESCRIPTION
The ASD relay is located in the Power Distribution Center (PDC). The PDC is located in the engine compartment. Refer to label on PDC cover for relay location.
OPERATION
A 12 volt signal at this input indicates to the PCM that the ASD has been activated. The relay is used to connect the oxygen sensor heater element, ignition coil and fuel injectors to 12 volt + power supply.
This input is used Only to sense that the ASD relay is energized. If the PCM does not see 12 volts at this input when the ASD should be activated, it will set a Diagnostic Trouble Code (DTC).
BATTERY TEMPERATURE SENSOR-PCM INPUT
OPERATION
Provides a signal to the PCM corresponding to the battery temperature.
BATTERY VOLTAGE-PCM INPUT
OPERATION
If battery voltage is low, the PCM will increase injector pulse width (period of time that the injector is energized). This is done to compensate for the reduced flow through injector caused by the lowered voltage.
BRAKE SWITCH-PCM INPUT
OPERATION
When the brake light switch is activated, the Powertrain Control Module (PCM) receives an input indicating that the brakes are being applied. After receiving this input, the PCM maintains idle speed to a scheduled rpm through control of the Idle Air Control (IAC) motor. The brake switch input is also used to disable vent and vacuum solenoid output signals to the speed control servo.
FIVE VOLT SENSOR SUPPLY-PRIMARY
OPERATION
Supplies the required 5 volt power source to the crankshaft position sensor, camshaft position sensor, MAP sensor and throttle position sensor.
FIVE VOLT SENSOR SUPPLY-SECONDARY
OPERATION
Supplies the required 5 volt source to certain sensors.
ENGINE COOLANT TEMPERATURE SENSOR- PCM INPUT
DESCRIPTION
The engine coolant temperature (ECT) sensor is used to sense engine coolant temperature. The sensor protrudes into an engine water jacket.
OPERATION
The ECT sensor provides an input voltage to the Powertrain Control Module (PCM) relating coolant temperature. The PCM uses this input along with inputs from other sensors to determine injector pulse width and ignition timing. As coolant temperature varies, the coolant temperature sensor resistance will change. This change in resistance results in a different input voltage to the PCM.
When the engine is cold, the PCM will operate in Open Loop cycle. It will demand slightly richer air-fuel mixtures and higher idle speeds. This is done until normal operating temperatures are reached.
GENERATOR OUTPUT-PCM INPUT
OPERATION
Provides a charging system voltage input to the Powertrain Control Module (PCM). It is sensed at the battery input to the PCM.
OXYGEN SENSOR-PCM INPUT
DESCRIPTION
The oxygen sensors (O2S) are attached to, and protrude in to, the vehicle exhaust system.
OPERATION
The sensors produce voltages from 0 to 1 volt, depending upon the oxygen content of the exhaust gas. When a large amount of oxygen is present (caused by a lean air/fuel mixture), the sensors produces a low voltage. When there is a lesser amount present (rich air/fuel mixture) it produces a higher voltage. By monitoring the oxygen content and converting it to electrical voltage, the sensors act as a rich-lean switches.
In Closed Loop operation, the PCM monitors certain O2 sensor input(s) along with other inputs, and adjusts the injector pulse width accordingly. During Open Loop operation, the PCM ignores the O2 sensor input. The PCM adjusts injector pulse width based on preprogrammed (fixed) values and inputs from other sensors.
The oxygen sensors are equipped with a heating element that keeps the sensors at proper operating temperature during all operating modes. Maintaining correct sensor temperature at all times allows the system to enter into closed loop operation sooner. Also, it allows the system to remain in closed loop operation during periods of extended idle. Certain emissions packages use the Automatic Shutdown (ASD) relay to supply battery voltage to the heating elements. Other emissions packages use separate oxygen sensor relays to supply battery voltage to the heating elements.
IGNITION CIRCUIT SENSE-PCM INPUT
OPERATION
The ignition circuit sense input tells the Powertrain Control Module (PCM) the ignition switch has energized the ignition circuit.
INTAKE MANIFOLD AIR TEMPERATURE SENSOR-PCM INPUT
DESCRIPTION
The Intake Manifold Air temperature (IAT) sensor is installed in the intake manifold with the sensor element extending into the air stream.
OPERATION
The IAT sensor provides an input voltage to the Powertrain Control Module (PCM) indicating intake manifold air temperature. The input is used along with inputs from other sensors to determine injector pulse width. As the temperature of the air-fuel stream in the manifold varies, the sensor resistance changes. This results in a different input voltage to the PCM.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR-PCM INPUT
DESCRIPTION
The MAP sensor is mounted to the engine throttle body.
OPERATION
The MAP sensor reacts to absolute pressure in the intake manifold. It provides an input voltage to the Powertrain Control Module (PCM). As engine load changes, manifold pressure varies. The change in manifold pressure causes MAP sensor voltage to change. The change in MAP sensor voltage results in a different input voltage to the PCM. The input voltage level supplies the PCM with information about ambient barometric pressure during engine start-up (cranking) and engine load while the engine is running. The PCM uses this input along with inputs from other sensors to adjust air-fuel mixture.
OIL PRESSURE SENSOR-PCM INPUT
DESCRIPTION
The engine oil pressure sensor (sending unit) is located in an engine oil pressure gallery.
OPERATION
A signal is sent from the oil pressure sensor to the Powertrain Control Module (PCM) relating to engine oil pressure.
POWER GROUND OPERATION
The power ground is used to control ground circuits for the following Powertrain Control Module (PCM) loads:
- Generator field winding Fuel injectors
- Ignition coil(s)
- Certain relays/solenoids
SENSOR RETURN-PCM INPUT
OPERATION
Sensor Return provides a low noise ground reference for all engine control system sensors.
THROTTLE POSITION SENSOR (TPS)-PCM INPUT
DESCRIPTION
The throttle position sensor (TPS) is mounted on the throttle body
OPERATION
The TPS is a variable resistor that provides the powertrain control module (PCM) with an input signal (voltage) that represents throttle blade position. The sensor is connected to the throttle blade shaft. As the position of the throttle blade changes, the resistance of the TPS changes.
The PCM supplies approximately 5 volts to the TPS. The TPS output voltage (input signal to the PCM) represents the throttle blade position. The PCM receives an input signal voltage from the TPS. This will vary in an approximate range of from 0.26 volts at minimum throttle opening (idle), to 4.49 volts at wide open throttle. Along with inputs from other sensors, the PCM uses the TPS input to determine current engine operating conditions. In response to engine operating conditions, the PCM will adjust fuel injector pulse width and ignition timing.
VEHICLE SPEED AND DISTANCE-PCM INPUT
OPERATION
Vehicle speed and distance covered are measured by the Rear Wheel Speed Sensor. The sensor is mounted to the rear axle. A signal is sent from this sensor to the Controller Antilock Brake (CAB) computer. A signal is then sent from the CAB to the Powertrain Control Module (PCM) to determine vehicle speed and distance covered. The PCM will then determine strategies for fuel system and speed control system operation.