COMPUTERS AND INPUT SENSORS

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COMPUTERSAND INPUT SENSORS
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MICROCOMPUTER OPERATION HAPPENS IN STAGES
Memory
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INPUT STAGE

• INPUTS All sensors produce are a voltage signal
  of some type
• Some Inputs are conditioned before going to the
  microprocessor.
• Amplification
• A/D Conversion

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INPUT CONDITIONING

• Microprocessor can only process some types of
  signals
• Must amplify some signals
• Must convert analog signals to digital signals

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BINARY CODE

• A/D converter takes snapshot of analog signal
• Computers only understand 1s and 0s.
• 1 On
• 0 Off
• Voltages are classified into different ranges
• Each range is assigned a numeric value
• Values are translated into a binary code

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PROCESSING OPERATION

• Digital signal compared to lookup tables
• Information is sent to microprocessor
• Microprocessor decides what to do
• Issues a command to output actuator

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TYPES OF MEMORY

• 3 DIFFERENT TYPES
• READ ONLY MEMORY (ROM)
• RANDOM ACCESS MEMORY (RAM)
• KEEP ALIVE MEMORY (KAM)

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READ ONLY MEMORY

• Permanent memory
• Microprocessor can only read information from ROM
• Information cannot be erased
• Contains info such as programs, look up tables
  to tell how vehicle should perform. Data and
  formulas used to perform calculations
• Vehicle information of cylinders, valve size,
  transmission type, rear end

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RANDOM ACCESS MEMORY

• Information stored temporarily
• Can be written to or read from
• When Ignition is turned off, memory is erased.
• Used to store information from sensors, results
  of calculations and data subject to constant
  change.

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KEEP ALIVE MEMORY

• Information can be read, written and erased from
  KAM
• KAM is not lost when ignition key is turned off
• Disconnecting Battery will erase KAM
• KAM allows for adaptive strategies
• Stores diagnostic codes

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PROCESSOR LOCATION

• Usually under dash or inside car
• Sometimes under hood.
• Susceptible to water, dirt, dust, heat and
  vibration
• Some are built in to component
• Body Computers located many different places in
  vehicle.
• Some cars centrally locate all processors

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HANDLING THE PROCESSOR

• TOUCH THE VEHICLE CHASSIS TO DISCHARGE STATIC
  ELECTRICITY
• TURN POWER OFF BEFORE DISCONNECTING PROCESSOR
• BE SURE DVOM CONNECTIONS ARE CORRECT
• BE SURE TO USE THE CORRECT TEST INSTRUMENT

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OUTPUT STAGE

• Microprocessor issues commands in the form of
  voltages
• Can display information on a Scanner or Digital
  dash
• Can control hydraulic, vacuum or electrical
  components.

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OUTPUT DRIVERS

• Microprocessor send digital signals to output
  drivers
• Drivers usually do not send voltage to actuators
• Microprocessor controls actuator ground circuit

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INPUT SENSORS

• ALL SENSORS PERFORM SAME BASIC FUNCTION
• DETECT MECHANICAL CONDITION (MOVEMENT)
• CHEMICAL STATE CHANGE
• TEMPERATURE CONDITION
• ALL SENSORS CHANGE ABOVE INPUT INTO VOLTAGE
  SIGNALS THAT PROCESSOR CAN USE

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3 WIRE SENSORSREFERENCE VOLTAGE SENSOR OR
VOLTAGE MODIFIER

• VOLTAGE REFERENCE
• SIGNAL WIRE
• SIGNAL RETURN (GROUND)

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THROTTLE POSITION SENSOR

• CHANGES MECHANICAL ACTION INTO ELECTRICAL SIGNAL
• SOME ARE ADJUSTABLE
• SOME READ HIGH VOLTS AT IDLE, SOME LOW VOLTS AT
  IDLE

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TWO WIRE SENSORVOLTAGE MODIFIER

• SIGNAL CIRCUIT
• GROUND CIRCUIT
• TWO TYPES OF TERMISTORS
• NTC REDUCES OHMS WHEN TEMP INCREASES
• PTC INCREASES OHMS WHEN TEMP INCREASES

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MAF SENSOR

• USES HOT WIRE
• PCM MONITORS COLD WIRE TEMP.
• SENDS CURRENT TO HOT WIRE TO MAINTAIN 392 DEGREES
  ABOVE COLD WIRE
• AMOUNT OF CURRENT DETERMINES INTAKE AIR FLOW

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CYCLEDUTY CYCLEPULSE WIDTHFREQUENCY
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PULSE WIDTH

• LENGTH OF TIME IN MS, ACTUATOR IS ON
• IE, DURATION OF ON-TIME
• PULSE WIDTH MODULATION

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VANE AIR FLOW METER

• USES THREE TYPES OF VOLTAGE MODIFIERS
• SWITCH
• POTENTIOMETER
• THERMISTOR
• MOVES DOOR TO DETERMINE AIR FLOW

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WHEATSTONE BRIDGE

• THREE FIXED AND ONE VARIABLE RESISTOR
• PCM ALWAYS TO BALANCE THE BRIDGE
• USED TO MEASURE PRESSURE AND MECHANICAL STRAIN

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VOLTAGE GENERATOR

• GENERATES IT OWN VOLTAGE SIGNAL
• COMPARES INSIDE AIR TO OUTSIDE AIR
• SIGNAL IS .1 TO 1.0 VOLT
• LOW VOLTAGE MEANS SENSING LEAN
• HIGH VOLTAGE MEANS SENSING RICH

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O2 SENSOR SIGNAL

• Signal range is between 0.0 and 1.0volt
• Normal operation is from 0.2 to 0.8 volts
• PCM will always try to do the opposite from what
  02 sensor is signaling

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02 CROSSCOUNTS
Generally, about 2 to 3 crosscounts is normal
operation
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ZIRCONIA SENSOR
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TITANIA SENSOR
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DIAGNOSTIC LOGIC TREE

• LOGIC TREE OR DIAGNOSTIC CHART
• SOME CHARTS INCLUDE EXPLANATIONS
• MANY MANUFACTUERS USE THIS TYPE DIAGNOSTICS

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LOOK UP TABLE USED TO DETERMINE BLOCK
LEARN/INTERGRATOR
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SCANNER

• SCANNERS READ CODES AND DATA STREAMS
• TEST ACTUATORS
• GRAPHING
• LAB SCOPE
• DVOM
• TECHNICAL INFO

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GM PROM

• CONTAINS SPECIFIC PROGRAMS SUCH AS SPARK
  ADVANCE, FUEL INJECTION
• SOME ARE ELECTRONICALLY ERASABLE
• REPLACEABLE SEPARATE FROM PCM

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CODE CHART

• SELF DIAGNOSTICS (SELF TEST MODE)
• HARD FAULTS
• SOFT CODES OR MEMORY CODES
• ACCESS TROUBLE CODES WITH SCANNER OR BY MANUAL
  METHOD
• ERASING FAULT CODES

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DATA LINK CONNECTORS(DLC)