Computers and Control Systems: Description and Operation

The electronic engine controls consist of the following:
- Powertrain Control Module (PCM)
- Throttle Position (TP) sensor
- Idle Air Control (IAC) valve
- Engine Coolant Temperature (ECT) sensor
- Camshaft Position (CMP) sensor
- Camshaft Synchronizer
- Crankshaft Position (CKP) sensor
- Mass Air Flow (MAF) sensor
- Intake Air Temperature (IAT) sensor
- Heated Oxygen Sensor (HO2S)
- Knock Sensor (KS)

The PCM performs the following functions:
- accepts input from various engine sensors to compute the required fuel flow rate necessary to maintain a prescribed air/fuel ratio throughout the entire engine operational range.
- outputs a command to the fuel injectors to meter the appropriate quantity of fuel.
- determines and compensates for the age of the vehicle and its uniqueness, also automatically senses and compensates for changes in altitude.

The TP sensor:
- sends the PCM a signal indicating the throttle plate angle.
- is the main input to the PCM from the driver.

The IAC valve:
- controls bypass air around the throttle plate at low speeds.
- is controlled by the PCM.

The ECT sensor:
- sends the PCM a signal indicating engine temperature.
- resistance decreases as coolant temperature increases.

The CMP sensor:
- sends the PCM a signal indicating camshaft position used for fuel synchronization.

The CKP sensor:
- sends the PCM a signal indicating crankshaft position.
- is essential for calculating spark timing.

The MAF sensor:
- uses a hot wire sensing element to measure the amount of air entering the engine. Air passing over the hot wire causes it to cool.

The IAT sensor:
- sends the PCM a signal indicating the temperature of the air entering the engine.
- is repaired as an assembly with the MAF.

The front HO2S:
- creates a voltage signal dependent on exhaust oxygen content.
- provides feedback information to the PCM used to calculate fuel delivery.

The rear HO2S:
- monitors oxygen content after it flows through the catalytic converter.
- provides a voltage to the PCM used to calculate catalytic converter integrity.

The KS:
- is used to detect engine detonation.
- sends a voltage signal to the PCM.
- is able to provide a signal which retards the ignition timing, as necessary.