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
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
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.
Fig. 2 Camshaft Position Sensor Location:
CAMSHAFT POSITION SENSOR-PCM INPUT
The camshaft position sensor is located on the timing chain case/cover on the left-front side of the engine (Fig. 2).
The camshaft position sensor is used in conjunction with the crankshaft position sensor to differentiate between fuel injection and spark events. It is also used to synchronize the fuel injectors with their respective cylinders. The sensor generates electrical pulses. These pulses (signals) are sent to the power- train control module (PCM). The PCM will then determine crankshaft position from both the camshaft position sensor and crankshaft position sensor.
Fig. 3 Camshaft Sprocket:
A low and high area are machined into the camshaft drive gear (Fig. 3). The sensor is positioned in the timing gear cover so that a small air gap (Fig. 3) exists between the face of sensor and the high machined area of cam gear.
When the cam gear is rotating, the sensor will detect the machined low area. Input voltage from the sensor to the PCM will then switch from a low (approximately 0.3 volts) to a high (approximately 5 volts). When the sensor detects the high machined area, the input voltage switches back low to approximately 0.3 volts.
Fig. 4 Timing Slots on Crankshaft:
CRANKSHAFT POSITION SENSOR-PCM INPUT
The crankshaft position sensor detects slots cut into a disk in the middle of the crankshaft (Fig. 4). There are a 5 sets of slots. Each set contains 2 slots, for a total of 10 slots. Basic timing is determined by the position of the last slot in each group. Once the PCM senses the last slot, it determines crankshaft position (next piston at TDC) from the camshaft position sensor input. During cranking, it may take the PCM up to one engine revolution to determine crankshaft position.
The PCM uses the camshaft reference sensor to determine injector sequence. Once crankshaft position has been determined, the PCM begins energizing the injectors in sequence. The PCM determines ignition timing from the crankshaft timing sensor.
Fig. 5 Crankshaft Position Sensor Location:
The crankshaft position sensor is located in the passengers side of the engine block, below the exhaust manifold (Fig. 5).
Fig. 6 Engine Coolant Temperature Sensor:
ENGINE COOLANT TEMPERATURE SENSOR-PCM INPUT
The engine coolant temperature sensor threads into the front of the driver side cylinder head (Fig. 6). 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 air-fuel 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 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 CCD bus circuits.
HEATED OXYGEN SENSOR (O2S SENSOR)-PCM INPUT
As vehicles accumulate mileage, the catalytic converter deteriorates. The deterioration results in a less efficient catalyst. To monitor catalytic converter deterioration, the fuel injection system uses two heated oxygen sensors in each side of the exhaust system (4 total). One sensor upstream of the catalytic converter, one downstream of the converter. The PCM compares the reading from the sensors to calculate the catalytic converter 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 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 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 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 all 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.
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 downstream heated oxygen sensor threads into the outlet pipe at the rear of the catalytic converter. The downstream heated oxygen sensor input is used to detect catalytic converter deterioration. As the converter 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 converter efficiency.
IGNITION CIRCUIT SENSE-PCM INPUT
The ignition circuit sense input tells the Power- train Control Module (PCM) the ignition switch has energized the ignition circuit. Refer to the wiring diagrams for circuit information.
Fig. 7 Intake Air Temperature Sensor:
INTAKE AIR TEMPERATURE SENSOR-PCM INPUT
The Intake Air Temperature Sensor threads into the air cleaner. The sensor measures air temperature (Fig. 7). The intake air temperature sensor input is one of the inputs the PCM monitors to determine the required injector pulse width.
Fig. 8 Map Sensor:
MANIFOLD ABSOLUTE PRESSURE 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 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.
The MAP sensor (Fig. 8) mounts to the drivers side intake manifold plenum.
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.
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.
Fig. 9 Throttle Position Sensor:
THROTTLE POSITION SENSOR-PCM INPUT
The fuel injection system uses only one Throttle Position Sensor (TPS). The TPS is mounted on the drivers side throttle body The sensor connects to the throttle blade shaft (Fig. 9). 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.
Fig. 10 Vehicle Speed Sensor; Skip Shift Solenoid and Reverse Lockout Fig 10 Solenoid:
VEHICLE SPEED SENSOR-PCM INPUT
The vehicle speed sensor is located on the drivers side of the transmission (Fig. 10). 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.