PCM Inputs

A/C Request
The A/C request input is received from the A/C control head. When the A/C is turned On, a B+ signal from the A/C switch, located in the A/C control head, is sent to the PCM. If the A/C low- and high-pressure switches are closed then the B+ signal is received by the PCM. This signal notifies the PCM that the operator of the vehicle has requested that the A/C system be turned On. If engines conditions allow, the PCM will energize the A/C coil relay by supplying a ground.

Diagnostic Request
The diagnostic request input is received from the data link connector (DLC) connector. When this line is grounded, the PCM will output fault codes, if any exist. If there are no codes set, the PCM will flash a DTC 12.

Inlet Air Temperature Sensor

Temperature - Resistance Chart For Sensors:

The inlet air temperature (IAT) sensor is a thermistor-type sensor mounted in the engine inlet air system. A thermistor resists the flow of electricity similar to a resistor. However, the resistance of a thermistor increases as the temperature drops. For example, at a low air temperature a thermistor produces a high resistance of 93k ohms at -40°C (-40°F), while a high temperature causes low resistance of 65 ohms at 140°C (248°F).

The inlet air temperature sensor is a two-wire sensor that receives a reference signal voltage from the PCM to sensor pin B and a sensor reference ground from the PCM to sensor pin A.

The PCM supplies the 5-volt reference signal to the inlet air temperature sensor through a current-limiting resistor located inside the PCM. This signal is received by the PCM and indicates the temperature of the air entering the engine. This sensor input is used by the PCM for fuel enrichment, ignition timing, EGR operation, canister purge control, idle speed control, and Closed Loop fuel control.

The chart lists the resistances of the inlet air temperature sensor and coolant temperature sensor as compared to sensor resistance.

Engine Coolant Temperature Sensor

Temperature - Resistance Chart For Sensors:

The engine coolant temperature (ECT) sensor is mounted in a coolant passage located in the cylinder head. The engine coolant temperature sensor is a thermistor-type sensor. A thermistor resists the flow of electricity similar to a resistor. However, the resistance of a thermistor increases as the temperature drops. For example, at a low air temperature a thermistor produces a high resistance of 93k ohms at -40°C (-40°F), while a high temperature causes low resistance of 65 ohms at 140°C (248°F).

The engine coolant temperature sensor is a two-wire sensor that receives a reference signal voltage from the PCM to sensor pin B and a sensor reference ground from the PCM to sensor pin A.

The PCM supplies the 5-volt reference signal to the engine coolant temperature sensor through a current-limiting resistor located inside the PCM. The signal received by the PCM indicates the temperature of the engine coolant, which is an indication of engine operating temperature. This sensor input is used by the PCM for fuel enrichment, ignition timing, EGR operation, canister purge control, idle speed control, and Closed Loop fuel control.

Manifold Absolute Pressure Sensor
The manifold absolute pressure (MAP) sensor is mounted above the intake manifold on the rocker cover on the base engine. On the performance engine it is mounted on the intake manifold. The MAP sensor measures the intake manifold pressure. Engine vacuum is related to engine load and speed changes. A high vacuum signal indicates a low intake manifold pressure. A low vacuum signal indicates a high intake manifold pressure. The higher the pressure signal, the greater the load being placed on the engine.

The MAP sensor voltage is scaled by the PCM to pressure (kPa or psi). A high pressure (atmospheric pressure) produces an output of 4.5-5.0 volts, about 95-105 kPa (14-15 psi). A low pressure (engine vacuum) produces about 0.5-0.90 volts, about 37-50 kPa (5-7 psi). The MAP sensor is also used to calculate barometric pressure under certain conditions.

By monitoring the MAP sensor output voltage signal, the PCM determines the manifold pressure and can increase or decrease the injector On-time (or pulse width). The PCM also uses the MAP sensor signal to help control ignition timing.

Oxygen Sensor
The oxygen sensor, mounted in the exhaust system, monitors the oxygen content of the exhaust gas stream. The oxygen sensor acts as an electro chemical cell, or battery, to produce a voltage in response to oxygen in the exhaust stream compared to oxygen content of the atmosphere. A lean mixture (high oxygen in the exhaust gas) produces a low voltage and a rich mixture (low oxygen content in the exhaust gas) produces a high voltage. The oxygen content in the exhaust reacts with the oxygen sensor to produce a voltage output. The voltage signal ranges from approximately 100 millivolts (0.1 volt) for a lean mixture to 900 millivolts (0.9 volt) for a rich mixture.

By monitoring the voltage output of the oxygen sensor, the PCM will know what fuel mixture command is required for the fuel injector.

The oxygen sensor operates between 275°C (527°F) to 850°C (1562°F).

The oxygen sensor ground is located on the back of the engine block.

Throttle Position Sensor
The throttle position (TP) sensor is mounted to the throttle body and connected to the throttle plate shaft. The throttle position is a potentiometer with a five volt reference input and a signal ground supplied by the PCM. A sensor output signal to the PCM is a DC signal that varies according to throttle position angle. As the throttle angle changes the signal to the PCM varies.

At a closed throttle position, the output of the throttle position sensor is low (approximately 0.5 volt). As the throttle plate opens, the output signal increases so that, at wide-open throttle, the output voltage will be high (approximately five volts).

A noisy throttle position sensor at idle, varying more than four counts will disrupt closed loop engine idle control.

Electronic Ignition Module
The electronic ignition (EI) module receives engine rpm from the crankshaft position sensor and relays this information to the PCM.

Knock Sensor
The knock sensor (KS) is mounted in the engine block near the cylinders and is used to detect abnormal vibration (spark knocking) within the engine block. The sensor produces an AC output voltage which increases with the severity of the engine knock. The PCM will reduce spark timing, to reduce engine knock.

This retard of spark timing allows the engine to use maximum spark advance to improve driveability and fuel economy.

The knock sensor signal is only used during the TDC combustion event, which is determined by the 6X signal (knock windowing).

Vehicle Speed Sensor
The vehicle speed sensor (VSS) is a variable reluctance pulse generator that senses the transaxle output. It operates between 0-161 km/h (0-120 mph).

The VSS informs the PCM of vehicle speed.

Ignition on Input
The PCM receives a signal from the ignition switch when the key is placed in the Run or Crank position. This signals the PCM that the vehicle is about to be started. The removal of this signal informs the PCM that the engine has been turned-off.

Battery B+ Input
The battery B+ line is fed directly from the battery. This allows the PCM to retain its memory when the ignition is turned-off.