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5 VOLT SUPPLY - PCM OUTPUT
The PCM supplies 5 volts to the following sensors:
- A/C pressure transducer
- Engine coolant temperature sensor
- Manifold absolute pressure sensor
- Throttle position sensor
- Linear EGR solenoid

8 VOLT SUPPLY - PCM OUTPUT
The PCM supplies 8 volts to the crankshaft position sensor, camshaft position sensor.

AIR CONDITIONING PRESSURE TRANSDUCER - PCM INPUT
The 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 OBD II.

The 5 volt and 8 volt regulators are protected from shorts to ground. This protection allows diagnostics to be performed should the five voltpower 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.

Camshaft Position Sensor (SOHC):

CAMSHAFT POSITION SENSOR - PCM INPUT
The camshaft position sensor attaches to the rear of the cylinder head. The PCM determines fuel injection synchronization and cylinder identification from inputs provided by the camshaft position sensor and crankshaft position sensor. From the two inputs, the PCM determines crankshaft position.

The PCM sends approximately 8 volts to the hall affect sensor. This voltage is required to operate the hall effect chip and the electronics inside the sensor. A ground for the sensor is provided through the sensor return circuit. The input to the PAM occurs on a 5 volt output reference circuit.

Target Magnet - Typical:

Target Magnet Polarity:

A target magnet attaches to the rear of the camshaft and indexes to the correct position. The target magnet has four different poles arranged in an asymmetrical pattern. As the target magnet rotates, the camshaft position sensor senses the change in polarity. The sensor output switch switches from high (5.0 volts) to low (0.5 volts) as the target magnet rotates. When the north pole of the target magnet passes under the sensor, the output switches high. The sensor output switches low when the south pole of the target magnet passes underneath.

The sensor also acts as a thrust plate to control camshaft endplay.

CLUTCH INTERLOCK/UPSTOP SWITCH

Clutch Interlock/Upstop Switch:

Clutch/Brake Pedal Bracket Assembly:

The clutch interlock/upstop switch is an assembly consisting of two switches: an engine starter inhibit switch (interlock) and a clutch pedal upstop switch. The switch assembly is located in the clutch/brake pedal bracket assembly, each switch being fastened by four plastic wing tabs.

[1][2]Clutch Interlock Switch
The clutch interlock switch prevents engine starter operation and inadvertent vehicle movement with the clutch engaged and the transaxle in gear.

The switch is open while the clutch pedal is at rest. When the clutch pedal is fully depressed, the pedal blade contacts and closes the switch, sending signal to the PCM, allowing engine starter operation. The interlock switch is not adjustable.

Clutch Pedal Upstop Switch
With the clutch pedal at rest, the clutch pedal upstop switch is closed, allowing speed control operation. When the clutch pedal is depressed, the upstop switch opens and signals the PCM to cancel speed control operation, and enter a modified engine calibration schedule to improve driveability during gear-to-gear shifts. The upstop switch is not adjustable.

CRANKSHAFT POSITION SENSOR - PCM INPUT

Crankshaft Position Sensor:

The crankshaft position sensor mounts to the front of the engine block.

Timing Reference Notches:

The PCM determines what cylinder to fire from the crankshaft position sensor input and the camshaft position sensor input. The second crankshaft counterweight has two sets of four timing reference notches including a 60 degree signature notch. From the crankshaft position sensor input the PCM determines engine speed and crankshaft angle (position).

The notches generate pulses from high to low in the crankshaft position sensor output voltage. When a metal portion of the counterweight aligns with the crankshaft position sensor the sensor output voltage goes low (less than 0.5 volts). When a notch aligns with the sensor, voltage goes high (5.0 volts). As a group of notches pass under the sensor, the output voltage switches from low (metal) to high (notch) then back to low.

If available, an oscilloscope can display the square wave patterns of each voltage pulses. From the width of the output voltage pulses, the PCM calculates engine speed. The width of the pulses represent the amount of time the output voltage stays high before switching back to low. The period of time the sensor output voltage stays high before switching back to low is referred to as pulse width. The faster the engine is operating, the smaller the pulse width on the oscilloscope.

By counting the pulses and referencing the pulse from the 60 degree signature notch, the PCM calculates crankshaft angle (position). In each group of timing reference notches, the first notch represents 69 ° Before Top Dead Center (BTDC). The second notch represents 49 ° BTDC. The third notch represents 29 ° BTDC. The last notch in each set represents 9 ° BTDC.

The timing reference notches are machined at 20 degree increments. From the voltage pulse width the PCM tells the difference between the timing reference notches and the 60 degree signature notch. The 60 degree signature notch produces a longer pulse width than the smaller timing reference notches. If the Camshaft Position Sensor input switches from high to low when the 60 degree signature notch passes under the Crankshaft Position Sensor, the PCM knows cylinder number one is the next cylinder at TDC.

The PCM uses the Crankshaft Position Sensor to calculate the following: Engine rpm, TDC number 1 and 4, ignition coil synchronization, injection synchronization, camshaft-to-crankshaft misalignment where applicable (timing belt skipped 1 tooth or more diagnostic trouble code).

The PCM sends approximately 9 volts to the Hall-effect sensor. This voltage is required to operate the Hall-effect chip and the electronics inside the sensor.

A ground for the sensor is provided through the sensor return circuit. The input to the PCM occurs on a 5 volt output reference circuit.

ENGINE COOLANT TEMPERATURE SENSOR - PCM INPUT

Engine Coolant Temperature Sensor (SOHC):

The coolant sensor threads into the rear of the cylinder head, next to the camshaft position sensor. New sensors have sealant applied to the threads.

The ECT Sensor is a Negative Thermal Coefficient (NTC), dual range Sensor. The resistance of the ECT Sensor changes as coolant temperature changes. This results in different input voltages to the PCM. The PCM also uses the ECT Sensor input to operate the low and high speed radiator cooling fans.

The combination coolant temperature sensor has two elements. One element supplies coolant temperature signal to the PCM. The other element supplies coolant temperature signal to the instrument panel gauge cluster. The PCM determines engine coolant temperature from the coolant temperature sensor.

As coolant temperature varies the coolant temperature sensors resistance changes resulting in a different input voltage to the PCM and the instrument panel gauge cluster.

When the engine is cold, the PCM will provide slightly richer air-fuel mixtures and higher idle speeds until normal operating temperatures are reached.

The PCM has a dual temperature range program for better sensor accuracy at cold temperatures. At key-ON the PCM sends a regulated five volt signal through a 10,000 ohm resistor to the sensor. When the sensed voltage reaches approximately 1.25 volts the PCM turns on the transistor. The transistor connects a 1000 ohm resistor in parallel with the 10,000 ohm resistor. With this drop in resistance the PCM recognizes an increase in voltage on the input circuit.

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 (O2 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:

Heated Oxygen Sensor Systems:

The downstream heated oxygen sensor threads into the system depending on emission package. Federal package the O2s is mounted after the catalytic convertor, ULEV package the O2s is mounted mid catalytic convertor, ULEV package is mounted between the catalytic convertor.

Types Of O2 Sensors:

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 02 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

Inlet Air Temperature Sensor:

The IAT sensor attaches to the intake air duct. The IAT Sensor is a Negative Temperature Coefficient (NTC) Sensor that provides information to the PCM regarding the temperature of the air entering the intake manifold.

Intake Air Temperature
The Intake Air Temperature sensor replaces the Intake Air Temperature sensor and the Battery Temperature Sensor. The PCM uses the information from the Intake Air Temperature sensor to determine values to use as an Intake Air Temperature sensor and a Battery Temperature Sensor.

The Intake Air Temperature (IAT) sensor value is used by the PCM to determine air density.

The PCM uses this information to calculate:
- Injector pulse width
- Adjustment of ignition timing (to prevent spark knock at high intake air temperatures)

Battery Temperature
The Intake Air Temperature sensor replaces the Intake Air Temperature sensor and the Battery Temperature Sensor. The PCM uses the information from the Intake Air Temperature sensor to determine values for the PCM to use as an Intake Air Temperature sensor and a Battery Temperature Sensor.

The battery temperature information along with data from monitored line voltage (B+), is used by the PCM to vary the battery charging rate. System voltage will be higher at colder temperatures and is gradually reduced at warmer temperatures.

The battery temperature information is also used for OBD II diagnostics. Certain faults and OBD II monitors are either enabled or disabled depending upon the battery temperature sensor input (example: disable purge and EGR,enable LDP). Most OBD II monitors are disabled below 20 °F.