Inputs

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 5 sufficient for A/C system operation.


Automatic Shutdown (ASD) Sense -- PCM Input
The Automatic Shutdown (ASD) Sense 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
The PCM monitors the battery voltage input to determine fuel injector pulse width and generator field control.

If battery voltage is low the PCM will increase injector pulse width (period of time that the injector is energized).

Battery Temperature Sensor -- PCM Input
The PCM uses the temperature of the battery area to control the charge rate. The signal is used to regulate the system voltage. The system voltage is higher at cold temperatures and is gradually reduced as temperature is increased.

Brake Switch -- PCM Input
When the brake switch is activated, the 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 motor. The brake switch is. mounted on the brake pedal support bracket.

Fig. 3 Camshaft Position Sensor:

Fig. 5 Camshaft Sprocket:

Camshaft Position Sensor -- PCM Input
The camshaft position sensor provides cylinder identification to the powertrain control module (PCM) (Fig. 3). The sensor generates pulses as groups of notches on the camshaft sprocket pass underneath it (Fig. 5). The PCM keeps track of crankshaft rotation and identifies each cylinder by the pulses generated by the notches on the camshaft sprocket. Four crankshaft pulses follow each group of camshaft pulses.

When the PCM receives two cam pulses followed by the long flat spot on the camshaft sprocket, it knows that the crankshaft timing marks for cylinder one are next (on driveplate). When the PCM receives one camshaft pulse after the long flat spot on the sprocket, cylinder number two crankshaft timing marks are next. After 3 camshaft pulses, the PCM knows cylinder four crankshaft timing marks follow. One camshaft pulse after the three pulses indicates cylinder five. The two camshaft pulses after cylinder 5 signals cylinder six (Fig. 5). The PCM can synchronize on cylinders 1 or 4.

When metal aligns with the sensor, voltage goes low (less than 0.3 volts. When a notch aligns with the sensor, voltage spikes high (5.0 volts). As a group of notches pass under the sensor, the voltage switches from low (metal) to high (notch) then back to low. The number of notches determine the amount of pulses. If available, an oscilloscope can display the square wave patterns of each timing events.

Top dead center (TDC) does not occur when notches on the camshaft sprocket pass below the cylinder. TDC occurs after the camshaft pulse (or pulses) and after the 4 crankshaft pulses associated with the particular cylinder. The arrows and cylinder call outs on Figures 5 and 6 represent which cylinder the flat spot and notches identify, they do not indicate TDC position.

Fig. 7 Camshaft Position Sensor Location:

The camshaft position sensor is mounted in the flout of the timing case cover (Fig. 7).

Fig. 9 Timing Slots:

Crankshaft Position Sensor -- PCM Input
The crankshaft position sensor detects slots cut into the transmission driveplate extension. There are a 3 sets of slots. Each set contains 4 slots, for a total of 12 slots (Fig. 9). Basic timing set by the position of the last slot in each group. Once the powertrain control module (PCM) senses the last slot. it determines. crank-shaft position which piston will next be at (TDC) from the camshaft position sensor input. The 4 pulses generated by the crankshaft position sensor represent the (69, 49, 29, and 9) BTDC marks. It may take the PCM one engine revolution to determine crankshaft position.

The PCM uses. crankshaft position reference to determine injector sequence and ignition timing. Once the PCM determines crankshaft position, it begins energizing. the injectors in sequence.

Fig. 10 Crankshaft Position Sensor Location:

The crankshaft sensor is located on the passengers side of the transmission housing, above the differential housing (Fig. 10). The bottom of the sensor is positioned next to the drive plate.

Fig. 11 Engine Coolant Temperature Sensor:

Engine Coolant Temperature Sensor -- PCM Input
The engine coolant temperature sensor threads into the water jacket next to thermostat housing (Fig. 11). The sensor provides an input to the powertrain control module (PCM). As coolant temperature varies, the sensor resistance changes, resulting in a different input voltage to the PCM.

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

The engine coolant sensor input also determines operation of the low and high speed cooling fans.

Fuel Level Sensor -- PCM Input
The fuel level sensor sends a variable voltage 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 15 percent of its rated capacity.

Heated Oxygen Sensor (O2S Sensor) -- PCM Input
As vehicles accumulate mileage. the catalytic convertor deteriorates. The deterioration results in a less efficient catalyst. To monitor catalytic convertor deterioration, the fuel injection system uses two heated oxygen sensors. One sensor upstream of the catalytic convertor. one downstream of the convertor The PCM compares the reading from the sensors to calculate the catalytic convertor oxygen storage capacity and converter efficiency. Also. the PCM uses the upstream heated oxygen sensor input when adjusting injector pulse width.

When the catalytic converter efficiency drops below emission standards, the PCM stores a diagnostic trouble code and illuminates the malfunction indicator lamp (MIL).

The O2S 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 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 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 O2S 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.

Fig. 14 Upstream Heated Oxygen Sensor:

Upstream Oxygen Sensor
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.

The upstream oxygen sensor threads into the outlet flange of the exhaust manifold (Fig. 13) or (Fig. 14).

Fig. 13 Upstream Heated Oxygen Sensor:

Downstream Oxygen Sensor
The downstream heated oxygen sensor threads into the outlet pipe at the rear of the catalytic convertor (Fig. 15). The downstream heated oxygen sensor input is used to detect catalytic convertor deterioration. As the convertor deteriorates, the input from the downstream sensor begins to match the upstream sensor input except for a slight time delay By comparing the downstream heated oxygen sensor input to the input from the upstream sensor, the PCM calculates catalytic convertor efficiency.

Ignition Sense -- PCM Input
The ignition sense input informs the powertrain control module (PCM) that the ignition switch is in the crank or run position.

Fig. 17 MAP Sensor:

Manifold Absolute Pressure Sensor -- PCM Input
The powertrain control module (PCM) supplies a 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 cranking, before the engine starts running. the PCM determines atmospheric air pressure from the MAP sensor voltage. While the engine operates the PCM determines intake manifold pressure front the MAP sensor voltage. Based on MAP sensor voltage and inputs from other sensors, the PCM adjusts spark advance and the air/fuel mixture.

The MAP sensor mounts to the rear of the intake manifold plenum (Fig. 17). The Map sensor must be in the horizontal position.

Sensor Return -- PCM Input
The sensor return circuit provide a lower electrical noise ground reference for all of the systems sensors. The sensor return circuit connects to internal ground circuits within the powertrain control module.

Speed Control -- PCM Input
The speed control system provides five separate voltages (inputs to the Powertrain Control Module (PCM). The voltages correspond to the ON/OFF SET, RESUME and CANCEL.

The speed control ON voltage informs the PCM that the speed control system has been activated. The speed control SET voltage informs the PCM that a fixed vehicle speed has been selected. The speed control RESUME voltage indicates the previous fixed speed is requested. The speed control CANCEL voltage tells the PCM to deactivate hut retain set speed in memory (same as depressing the brake pedal). The speed control OFF voltage tells the PCM that the speed control system has deactivated.

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.

Park/Neutral Switch -- PCM Input
The automatic transaxle manual valve lever position sensor supplies the park/neutral input to the powertrain control module. The park/neutral switch input tells the PCM whether the transmission is in Park, Neutral. or a drive gear selection. This input effects idle speed, fuel injector pulse width and ignition timing.

Fig. 19 Throttle Position Sensor:

Throttle Position Sensor -- PCM Input
The throttle position sensor mounts to the side of the throttle body (Fig. 19).

The sensor connects to the throttle blade shaft. The TPS is a variable resistor that provides the powertrain control module (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 powertrain control module represents throttle blade position. The TPS output voltage to the PCM varies from approximately 0.6 volt at minimum throttle opening (idle) to a maximum of 4.5 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.

Transaxle Gear Engagement
Only the TCM supplies an input indicating transaxle gear engagement to the PCM over the CCD Bus. The input allows the PCM to adjust idle speed for smooth gear engagement.

Vehicle Speed And Distance -- PCM Input
The transmission control module supplies the road speed and distance traveled inputs to the PCM. From these inputs and the throttle position sensor input. the PCM determines when a deceleration condition occurs.