To piggyback onto Dan'* post.
MAF Sensor: Mass Air Flow, this sensor is a wire coil that is heated by the vehicle to a specific temperature. The amount of power required to maintain that temperature is how the sensor reads the amount of air passing the sensor.
MAP Sensor: Manifold Air Pressure: This sensor reads the pressure or vacuum in your Lower Intake Manifold (LIM).
IAC Sensor: Idle Air Control: This is technically called the IAC valve and is not a sensor. This valve controls the idle speed by controlling a vacuum leak into the motor.
C-shaft Positioning Sensor: Crankshaft Position Sensor: Abbreviated CKP to distinguish it from the CPS or Cam Position Sensor. The CKP reads the 3x and 18X spaces on the back of the harmonic balancer. It feeds this information to the PCM and ICM for timing and TDC references as well as being used in the determination of cylinder misfiring.
PCV: Postive Crankcase Ventilation: This is not a sensor, it is a valve that consists of a basic ball bearing in a can. It allows any positive pressure in the crankcase to push up into the intake and be burned.
EGR: Exhaust Gas Recirculation: This valve has sensors built in to determine the position and expected flow from the valve. This is used to add burned fuel into the cylinders in an effort to reduce fuel usage and cool cylinder temps.
TPS: Throttle Position Sensor: Reports the position of the throttle plate to the pcm and is used in many calculations including transmission shifting.
Oil Pressure Switch: aka Oil Pressure Sensor: Reports to the gauge the oil pressure in the motor.
CPS: Cam Position Sensor: Reports the cam magnet postion to the pcm in order to determine which cylinder to fire the coil pack for. Used mainly on startup.
ECT: Engine Coolant Temperature: This sensor is used to monitor coolant temp for both a gauge and pcm. PCM uses it to modify timing and fueling tables used in engine management calculations.
Oil Level Sensor: Used to tell the PCM that oil is present in the pan
KS: Knock Sensor: Used to monitor noise levels in the motor. This is used to retard timing (KR: Knock Retard) with predetonation.
O2 Sensor: Used by the pcm to interpret the accuracy of the maf sensor and fueling tables. Adjustments are made to the fueling based on input from this sensor.
If we move to the transmission there are a bunch more sensors.
Input Shaft Speed
Output Shaft Speed
Probably still many more I am not currently thinking of.
00 Regal GS: All kinds of cool stuff.