Inputs
AIR CONDITIONING PRESSURE TRANSDUCER - PCM INPUTThe Powertrain Control Module (PCM) monitors the A/C compressor discharge (high side) pressure through the air conditioning pressure transducer. The transducer supplies an input to the PCM. The PCM engages the A/C compressor clutch if pressure is sufficient for A/C system operation.
AUTOMATIC SHUTDOWN (ASD) SENSE - PCM INPUT
The ASD sense circuit informs the PCM when the ASD relay energizes. A 12 volt signal at this input indicates to the PCM that the ASD has been activated. This input is used only to sense that the ASD relay is energized.
When energized, the ASD relay supplies battery voltage to the fuel injectors, ignition coils and the heating element in each oxygen sensor, If the PCM does not receive 12 volts from this input after grounding the ASD relay, it sets a Diagnostic Trouble Code (DTC).
BATTERY VOLTAGE - PCM INPUT
In order for the PCM to operate, it must be supplied with battery voltage and ground. The PCM monitors the direct battery feed input to determine battery charging rate and to control the injector initial opening point. It also has back-up RAM memory used to store Diagnostic Trouble Codes (supply working DTCs). Direct battery feed is also used to perform key-OFF diagnostics and to supply working voltage to the controller for OBDII.
The five and eight volt regulators are protected from shorts to ground. This protection allows diagnostics to be performed should the five volt power supply become shorted to ground at any of the sensors. A short to ground in the five volt power supply will cause a "no-start" situation, There is a Diagnostic Trouble Code (DTC) if the five-volt power supply becomes shorted to ground. Refer to the Diagnostic Procedures for more details on any on-board diagnostic information.
If battery voltage is low the PCM will increase injector pulse width (period of time that the injector is energized).
The direct battery feed to the PCM is used as a reference point to sense battery voltage.
Effect on Fuel Injectors
Fuel injectors are rated for operation at a specific voltage. If the voltage increases, the plunger will open faster and further (more efficient) and conversely, if voltage is low the injector will be slow to open and will not open as far. Therefore, if sensed battery voltage drops, the PCM increases injector pulse-width to maintain the same volume of fuel through the injector.
Charging
The PCM uses sensed battery voltage to verify that target charging voltage (determined by Battery Temperature Sensor) is being reached. To maintain the target charging voltage, the PCM will full field the generator to 0.5 volt above target then turn OFF to 0.5 volt below target. This will continue to occur up to a 100 Hz frequency, 100 times per second.
BRAKE SWITCH - PCM INPUT
When the brake switch is activated, the PCM receives an input indicating that the brakes are being applied. The brake switch is mounted on the brake pedal support bracket.
ENGINE COOLANT TEMPERATURE SENSOR - PCM INPUT
Engine Coolant Temperature Sensor:
The engine coolant temperature sensor threads into the front of the driver side cylinder head.
The sensor provides an input to the PCM. As coolant temperature varies, the sensor resistance changes, resulting in a different input voltage to the PCM.
Until the engine reaches operating temperature, the PCM demands slightly richer air4uel mixtures and higher idle speeds.
This sensor is also used for cooling fan control and A/C cutoff at high coolant temperatures.
This 3-way sensor is also used for the water temperature gauge and dashboard warning light.
FUEL LEVEL SENSOR - PCM INPUT
The fuel gauge level sending unit is attached to the fuel pump module.
The fuel level sensor (fuel gauge sending unit) sends a signal to the PCM to indicate fuel level. The purpose of this feature is to prevent a false setting of misfire and fuel system monitor trouble codes if the fuel level is less than approximately 15 percent of its rated capacity. It is also used to send a signal for fuel gauge operation via the PCI bus circuits.
HEATED OXYGEN SENSOR (O2S SENSOR) - PCM INPUT
Upstream Heated Oxygen Sensor 1/1:
The upstream oxygen sensor threads into the outlet flange of the exhaust manifold.
Downstream Heated Oxygen Sensor 1/2:
The downstream heated oxygen sensor threads into the outlet pipe at the rear of the catalytic convertor.
The O2 sensors produce voltages from 0 to 1 volt, depending upon the oxygen content of the exhaust gas in the exhaust manifold. When a large amount of oxygen is present (caused by a lean air/fuel mixture), the sensors produce a voltage below 450 mv When there is a lesser amount present (rich air/fuel mixture) it produces a voltage above 450 mv. By monitoring the oxygen content and converting it to electrical voltage, the sensors act as a rich- lean switch,
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.
In Closed Loop operation the PCM monitors the O2 sensor input (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 Automatic Shutdown (ASD) relay supplies battery voltage to both the upstream and downstream heated oxygen sensors. The oxygen sensors are equipped with a heating element. The heating elements reduce the time required for the sensors to reach operating temperature.
Upstream Oxygen Sensor 1/1
The input from the upstream heated oxygen sensor tells the PCM the oxygen content of the exhaust gas. Based on this input, the PCM fine tunes the air-fuel ratio by adjusting injector pulse width.
The sensor input switches from 0 to 1 volt, depending upon the oxygen content of the exhaust gas in the exhaust manifold. When a large amount of oxygen is present (caused by a lean air-fuel mixture), the sensor produces voltage as low as 0.1 volt. When there is a lesser amount of oxygen present (rich air-fuel mixture) the sensor produces a voltage as high as 1.0 volt. By monitoring the oxygen content and converting it to electrical voltage, the sensor acts as a rich-lean switch.
The heating element in the sensor provides heat to the sensor ceramic element. Heating the sensor 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.
In Closed Loop, the PCM adjusts injector pulse width based on the upstream heated oxygen sensor input along with other inputs. In Open Loop, the PCM adjusts injector pulse width based on preprogrammed (fixed) values and inputs from other sensors.
Downstream Oxygen Sensor 1/2
The Downstream O2 Sensor has two functions. One function is measuring catalyst efficiency. This is an OBD II requirement. The oxygen content of the exhaust gasses has significantly less fluctuation than at the inlet if the converter is working properly. The PCM compares upstream and Downstream O2 Sensor switch rates under specific operating conditions to determine if the catalyst is functioning properly.
The other function is a downstream fuel control which was introduced in 1996. The upstream O2 goal varies within the window of operation of the O2 Sensor. In the past the goal was a preprogrammed fixed value based upon where it believed the catalyst operated most efficiently.
While the Upstream O2 Sensor input is used to maintain the 14.7:1 air/fuel ratio, variations in engines, exhaust systems and catalytic converters may cause this ratio to not be the most ideal for a particular catalyst and engine. To help maintain the catalyst operating at maximum efficiency, the PCM will fine tune the air/fuel ratio entering the catalyst based upon the oxygen content leaving the catalyst. This is accomplished by modifying the Upstream O2 Sensor voltage goal.
If the exhaust leaving the catalyst has too much oxygen (lean) the PCM increases the upstream O2 goal which increases fuel in the mixture causing less oxygen to be left over. Conversely, if the oxygen content leaving the catalyst has is too little oxygen (rich) the PCM decreases the upstream O2 goal down which removes fuel from the mixture causing more oxygen to be left over. This function only occurs during downstream closed loop mode operation.
IGNITION CIRCUIT SENSE - PCM INPUT
The ignition circuit sense input tells the Powertrain Control Module (PCM) the ignition switch has energized the ignition circuit.
Battery voltage is also supplied to the PCM through the Ignition Switch when the ignition is in the RUN or START position. This is called the "ignition sense" circuit and is used to "wake up" the PCM. Voltage on the ignition input can be as low as 6 volts and the PCM will still function. Voltage is supplied to this circuit to power the 8-volt regulator and to allow the PCM to perform fuel, ignition and emissions control functions. The battery voltage on this line is supplied to the 8-volt regulator which then passes on a power-up supply to the 5-volt regulator.
INTAKE AIR TEMPERATURE SENSOR - PCM INPUT
Intake Air Temperature Sensor:
The Intake Air Temperature Sensor threads into the air cleaner. The sensor measures air temperature.
The intake air temperature sensor input is one of the inputs the PCM monitors to determine the required injector pulse width.
MANIFOLD ABSOLUTE PRESSURE SENSOR - PCM INPUT
Map Sensor:
The MAP sensor mounts to the drivers side intake manifold plenum.
The PCM supplies 5 volts to the MAP sensor. The MAP sensor converts intake manifold pressure into voltage. The PCM monitors the MAP sensor output voltage. As vacuum increases, MAP sensor voltage decreases proportionately. Also, as vacuum decreases, MAP sensor voltage increases proportionately.
During Key-On, before cranking the engine, the PCM determines atmospheric air pressure from the MAP sensor voltage. While the engine operates, the PCM determines intake manifold pressure from the MAP sensor voltage. Based on MAP sensor voltage and inputs from other sensors, the PCM adjusts spark advance and the air/fuel mixture.
SENSOR RETURN - PCM INPUT
The sensor return circuit provides a low electrical noise ground reference for all of the systems sensors. The sensor return circuit connects to internal ground circuits within the Powertrain Control Module (PCM).
SCI RECEIVE - PCM INPUT
SCI Receive is the serial data communication receive circuit for the DRB scan tool. The Powertrain Control Module (PCM) receives data from the DRB through the SCI Receive circuit.
THROTTLE POSITION SENSOR - PCM INPUT
Throttle Position Sensor:
The TPS is mounted on the drivers side throttle body. The sensor connects to the throttle blade shaft.
The fuel injection system uses only one Throttle Position Sensor (TPS). The TPS is a variable resistor that provides the PCM with an input signal (voltage). The signal represents throttle blade position. 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 throttle blade position. The TPS output voltage to the PCM varies from approximately 0.5 volt at minimum throttle opening (idle) to 3.5 volts at wide open throttle. Along with inputs from other sensors, the PCM uses the TPS input to determine current engine operating conditions. The PCM also adjusts fuel injector pulse width and ignition timing based on these inputs.
VEHICLE SPEED SENSOR - PCM INPUT
Vehicle Speed Sensor, Skip Shift Solenoid And Reverse Locknut Solenoid:
The vehicle speed sensor is located on the drivers side of the transmission.
The Power Control Module (PCM) determines vehicle speed from the speed sensor input.
From the speed sensor input to the PCM determine the following:
- To prevent deceleration fuel cutoff at low vehicle speeds
- What gear the vehicle is operating in for 2-3 lockout
- Idle speed control delay time based on whether the vehicle is moving
- Cooling fan turns off at 77 mph, when accelerating, and turns back on at 67 mph.