Inputs

AIR CONDITIONING PRESSURE TRANSDUCER-PCM INPUT
OPERATION
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.

AIR CONDITIONING SWITCH SENSE-PCM INPUT
When the air conditioning or defrost switch is put in the ON position and the low pressure switch, combination valve, and high pressure switch close, the PCM receives an A/C input. After receiving this input, the PCM activates the A/C compressor clutch by grounding the A/C clutch relay. The PCM also adjusts idle speed to a scheduled RPM to compensate for increased engine load.

AUTOMATIC SHUTDOWN (ASD) SENSE-PCM INPUT
OPERATION
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
OPERATION
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).

BRAKE SWITCH-PCM INPUT
OPERATION
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.

CAMSHAFT POSITION SENSOR-PCM INPUT
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.

3.3/3.8L

Camshaft Position Sensor:

The sensor generates pulses as groups of notches on the camshaft sprocket pass underneath it. 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.

Camshaft Sprocket:

When the PCM receives two camshaft 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. The PCM can synchronize on cylinders 1 or 4.

When metal aligns with the sensor, voltage goes low (less than 0.5 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 Figure 4 represent which cylinder the flat spot and notches identify, they do not indicate TDC position.

Camshaft Position Sensor Location:

The camshaft position sensor is mounted to the top of the timing case cover. The bottom of the sensor is positioned above the camshaft sprocket.

The distance between the bottom of sensor and the camshaft sprocket is critical to the operation of the system. When servicing the camshaft position sensor, refer to the 3.3L and 3.8L Multi-Port Fuel Injection-Service Procedures.

2.4L

Camshaft Position Sensor:

Target Magnet:

Target Magnet Polarity:

The camshaft position sensor attaches to the rear of the cylinder head. 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 (0.30 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.

CRANKSHAFT POSITION SENSOR-PCM INPUT
3.0/3.3/3.8L

Crankshaft Position Sensor:

Timing Slots:

The crankshaft position sensor senses slots cut into the transaxle driveplate extension. There are 3 sets of slots. Each set contains 4 slots, for a total of 12 slots. Basic timing is set by the position of the last slot in each group. Once the PCM senses the last slot, it determines crankshaft position (which piston will next be at TDC) from the camshaft position sensor input. It may take the PCM one engine revolution to determine crankshaft position.

The PCM uses the crankshaft position sensor signal to determine injector sequence, ignition timing and presence of misfire. Once crankshaft position has been determined, the PCM begins energizing the injectors in sequence.

Crankshaft Position Sensor Location:

The crankshaft position sensor is located in the transaxle housing, above the vehicle speed sensor. The bottom of the sensor is positioned next to the drive plate. The distance between the bottom of sensor and the drive plate is critical to the operation of the system. When servicing the crankshaft position sensor, refer to the appropriate Multi-Port Fuel Injection Service Procedures.

2.4L

Timing Reference Notches:

The second crankshaft counterweight has machined into it two sets of four timing reference notches and 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 0.3 volts). When a notch aligns with the sensor, voltage spikes high (5.0 volts). As a group of notches pass under the sensor, the 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 pulse. 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 degrees before top dead center (BTDC). The second notch represents 49 degrees BTDC. The third notch represents 29 degrees. The last notch in each set represents 9 degrees before top dead center (TDC).

The timing reference notches are machined to a uniform width representing 13.6 degrees of crankshaft rotation. 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.

Crankshaft Position Sensor:

The crankshaft position sensor mounts to the engine block behind the generator, just above the oil filter.

ENGINE COOLANT TEMPERATURE SENSOR-PCM INPUT
The engine coolant temperature sensor is a variable resistor with a range of -40° C to 129° C (-40° F to 265° F).

The engine coolant temperature sensor provides an input voltage to the 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 is also used for cooling fan control.

3.0/3.3/3.8L

Engine Coolant Temperature Sensor:

The sensor is installed next to the thermostat housing.

2.4L

Engine Coolant Temperature Sensor:

The coolant sensor threads into the top of the thermostat housing. New sensors have sealant applied to the threads.

HEATED OXYGEN SENSOR (O2S SENSOR)-PCM INPUT
The O2S 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 input (along with other inputs) and adjusts the injector pulse width accordingly. During Open Loop operation the PCM ignores the 02 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 HEATED OXYGEN SENSOR

Heated Oxygen Sensor:

The upstream O2S is located in the exhaust manifold and provides an input voltage to the PCM. The input tells the PCM the oxygen content of the exhaust gas. The PCM uses this information to fine tune the air/fuel ratio by adjusting injector pulse width.

DOWNSTREAM HEATED OXYGEN SENSOR

Downstream Heated Oxygen Sensor:

The downstream heated oxygen sensor threads into the outlet pipe at the rear of the catalytic convertor. 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.

When the catalytic converter efficiency drops below emission standards, the PCM stores a diagnostic trouble code and illuminates the Malfunction Indicator Lamp (MIL). For more information, refer to Emission Control Systems.

KNOCK SENSOR-PCM INPUT
The knock sensor is only on the 2.4/3.3/3.8L engines, not used on the 3.0L engine.

Knock Sensor:

The knock sensor threads into the side of the cylinder block in front of the starter. When the knock sensor detects a knock in one of the cylinders, it sends an input signal to the PCM. In response, the PCM retards ignition timing for all cylinders by a scheduled amount.

Knock sensors contain a piezoelectric material which sends an input voltage (signal) to the PCM. As the intensity of the engine knock vibration increases, the knock sensor output voltage also increases.

MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR-PCM INPUT
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 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 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.

MAP Sensor:

The MAP sensor mounts to the intake manifold near the throttle body inlet to the manifold. The sensor connects electrically to the PCM.

SPEED CONTROL-PCM INPUT
OPERATION
The speed control system provides five separate voltages (inputs) to the Powertrain Control Module (PCM). The voltages correspond to the ON, OFF, SET, RESUME, CANCEL, and DECEL.

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 but retain set speed in memory (same as depressing the brake pedal). The speed control DECEL voltage informs the PCM to coast down to a new desired speed. The speed control OFF voltage tells the PCM that the speed control system has deactivated. Refer to the Speed Control for more speed control information.

TRANSAXLE PARK/NEUTRAL SWITCH-PCM INPUT
DESCRIPTION

Park Neutral Switch-4 Speed Electronic Automatic Transaxle-Typical:

The park/neutral switch is located on the transaxle housing.

OPERATION
If provides an input to the PCM indicating whether the automatic transaxle is in Park or Neutral. This input is used to determine idle speed (varying with gear selection) and ignition timing advance. The park neutral switch is sometimes referred to as the neutral safety switch.

Throttle Position Sensor:

THROTTLE POSITION SENSOR (TPS)-PCM INPUT
The TPS is mounted on the throttle body and connected to the throttle blade shaft. The TPS is a variable resistor that provides the (PCM) with an input signal (voltage) representing 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 the throttle blade position. The TPS output voltage to the PCM varies from approximately 0.5 volt at minimum throttle opening (idle) to 4 volts at wide open throttle. Along with inputs from other sensors, the PCM uses the TPS input to determine current engine operating conditions and adjust fuel injector pulse width and ignition timing.

VEHICLE SPEED AND DISTANCE-PCM INPUT
OPERATION
The transaxle output speed sensor supplies the vehicle speed and distance inputs to the PCM. The output speed sensor is located on the side of the transaxle.

The speed and distance signals, along with a closed throttle signal from the TPS, determine if a closed throttle deceleration or normal idle condition (vehicle stopped) exists. Under deceleration conditions, the PCM adjusts the idle air control motor to maintain a desired MAP value. Under idle conditions, the PCM adjusts the idle air control motor to maintain a desired engine speed.

INTAKE AIR TEMPERATURE SENSOR-PCM INPUT (2.4L ONLY)

Intake Air Temperature Sensor:

The Intake Air Temperature (IAT) sensor measures the temperature of the intake air as it enters the engine. The sensor supplies one of the inputs the PCM uses to determine injector pulse width and spark advance. The IAT sensor threads into the intake manifold .