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Crankshaft Position - in this case a Hall Effect switch in the distributor will indicate crankshaft
        speed and position.
Engine Coolant Temperature - a thermistor (a resistor that reduces resistance as it heats up)
        will indicate engine temperature.  It is located in the cooling system.
EGR Flow - uses a vacuum sensor to measure how much vacuum is applied to the EGR valve
        (which we will see later in the Emission Control section).
Exhaust Gas Oxygen Sensor - will measure the amount of oxygen left in the exhaust gases.  This
        sensor will not operate until it heats up - and many newer sensors have an electric heater
        built in so they will function properly.  The O2 sensor compares the amount of oxygen in
        the exhaust to the amount in the outside air and generates a small voltage.  A reading of
        less than 0.5 volts indicates a lean mixture (more oxygen).  A reading greater than 0.5 volts
        indicates a rich mixture (less oxygen).  This is the most important sensor in terms of fuel
        injection systems.  When the O2 sensor signal is not being used, the system is in Open
       Loop.  When the O2 signal is being used, the system is in Closed Loop.  Open Loop will
        occur when the sensor is cold or when the engine is under heavy load.
Intake air Temperature - is a thermistor located in the intake to measure the temperature of
        the air entering the engine.
Manifold Absolute Pressure (MAP) - will measure the pressure in the intake manifold.  It is
        also used to measure outside air (barometric) pressure when the ignition is first turned
        on, before the engine is started - and at wide open throttle, when there is no vacuum
        because it has been displaced by air.
Throttle Position Sensor - will indicate how far the throttle plate has been opened as the
        driver steps on the accelerator pedal.

Canister Purge Solenoid - is used to remove fuel vapours from a special canister - which will
        be covered in the Emission section of this course.
Throttle Air Bypass Solenoid - which will open and close to control airflow into the intake
        during idle or decelleration.
Fuel Injector - will have the pulse width varied depending on input information -mainly the
        O2 sensor reading.
EGR Solenoid - will regulate vacuum flow to the EGR valve - which is used to control Nitrous
        Oxide emissions - as we will see later.
Ignition Module - will control the current flowing through the ignition coil Primary winding,
        turning off current flow to make the magnetic field collapse and produce a spark at
        the appropriate time.

Brake Switch - an on-off switch that will send an on/off signal to the computer
Distance Sensor - that will measure vehicle speed and distance traveled.  This is used for
        fuel and spark control and to turn on the Maintenance Required light at the preset
        mileage setting (usually 80,000 km or 50,000 miles).
A/C Damped Pressure Cycling Switch - to indicate that the air conditioning is on and is
        putting additional load on the engine.
Speed Control Switch - turns the cruise control (speed control) on and off.
Neutral Safety Switch - which signals the computer the transmission is in Park or
        Neutral.
Heated Oxygen Sensor - which measures the amount of O2 in the exhaust system.
Coolant Temperature Sensor - uses a thermistor to indicate engine temperature.
Charge Temperature Sensor - uses a thermistor to indicate air temperature in the intake.
Distributor Reference Pickup - uses an optical sensor (description is in the Text) to measure
        engine speed and crankshaft position.
Throttle Position Sensor - which is a variable resistor that measures throttle opening.
Manifold Absolute Pressure (MAP) sensor - which measures engine manifold pressure
        and engine load.

Lock Up Torque Convertor Solenoid - a solenoid controlled by the computer that will cause
        the automatic transmission torque convertor to lock up to reduce slippage.  This results
        in better fuel economy and reduced emissions.
Check Engine Lamp (CEL)  - also known as a Malfunction Indicator Lamp (MIL) - is turned
        on by the computer when a fault in the sensors, computer or some outputs is detected.
A/C Cutout Relay - shuts off the air conditioning compressor under heavy load to reduce
        engine stress.
Radiator Fan Relay - turns on the radiator cooling fan at a preset engine temperature.
A/C Condenser Fan Relay - turns on a separate cooling fan for the air conditioning condenser
        when the A/C is on.
Auto Shut Down Relay - turns off the fuel pump when there is no ignition signal to prevent
        filling a non-operating engine with unburned fuel.
Automatic Idle Speed Motor - will vary the size of the opening bypassing the throttle plate
        to maintain correct idle speed and prevent stall during decelleration.
Purge Control Solenoid - allows fuel vapours from the tank to be recycled back to the
        intake to be burned.
EGR Diagnostic Solenoid - monitors the vacuum applied to the EGR valve (California
        emissions only).
Ignition Coil - primary current is switched on and off by the computer control circuits
        to control spark timing.
Fuel Pump - is turned on by the computer when the key is first switched on.
Alternator - the computer (SMEC - single module engine controller) has a voltage regulator
        control that helps maintain a steady output voltage to charge the battery and operate
        accessories when the vehicle is running.
Fuel Injectors - pulse width and timing is controlled by the SMEC.
Speed Control Servo - the integrated speed control is activated by the SMEC.