COMPUTERS AND INPUT SENSORS

cbc MICROCOMPUTER OPERATION HAPPENS IN STAGES Memory

cbc INPUT STAGE n INPUTS: All sensors produce are a voltage signal of some type n Some Inputs are “conditioned” before going to the microprocessor. –Amplification –A/D Conversion

cbc INPUT CONDITIONING n Microprocessor can only process some types of signals n Must amplify some signals n Must convert analog signals to digital signals

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

cbc PROCESSING OPERATION n Digital signal compared to lookup tables n Information is sent to microprocessor n Microprocessor decides what to do n Issues a command to output actuator

cbc TYPES OF MEMORY n 3 DIFFERENT TYPES n READ ONLY MEMORY (ROM) n RANDOM ACCESS MEMORY (RAM) n KEEP ALIVE MEMORY (KAM)

cbc READ ONLY MEMORY n Permanent memory n Microprocessor can only read information from ROM n Information cannot be erased n Contains info such as: programs, look up tables to tell how vehicle should perform. Data and formula’s used to perform calculations n Vehicle information: # of cylinders, valve size, transmission type, rear end

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

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

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

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

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

cbc OUTPUT DRIVERS n Microprocessor send digital signals to output drivers n Drivers usually do not send voltage to actuators n Microprocessor controls actuator ground circuit

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

cbc 3 WIRE SENSORS REFERENCE VOLTAGE SENSOR OR VOLTAGE MODIFIER n VOLTAGE REFERENCE n SIGNAL WIRE n SIGNAL RETURN (GROUND)

cbc THROTTLE POSITION SENSOR n CHANGES MECHANICAL ACTION INTO ELECTRICAL SIGNAL n SOME ARE ADJUSTABLE n SOME READ HIGH VOLTS AT IDLE, SOME LOW VOLTS AT IDLE

cbc TWO WIRE SENSOR VOLTAGE MODIFIER n SIGNAL CIRCUIT n GROUND CIRCUIT n TWO TYPES OF TERMISTORS –NTC = REDUCES OHMS WHEN TEMP INCREASES –PTC = INCREASES OHMS WHEN TEMP INCREASES

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

cbc CYCLE DUTY CYCLE PULSE WIDTH FREQUENCY

cbc PULSE WIDTH n LENGTH OF TIME IN MS, ACTUATOR IS ON n IE, “DURATION OF ON-TIME” n PULSE WIDTH MODULATION

cbc VANE AIR FLOW METER n USES THREE TYPES OF VOLTAGE MODIFIERS –SWITCH –POTENTIOMETER –THERMISTOR n MOVES DOOR TO DETERMINE AIR FLOW

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

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

cbc O2 SENSOR SIGNAL n Signal range is between 0.0 and 1.0volt n Normal operation is from 0.2 to 0.8 volts n PCM will always try to do the opposite from what 02 sensor is signaling

cbc 02 CROSSCOUNTS Generally, about 2 to 3 crosscounts is normal operation

cbc ZIRCONIA SENSOR

cbc TITANIA SENSOR

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

cbc LOOK UP TABLE USED TO DETERMINE BLOCK LEARN/INTERGRATOR

cbc SCANNER n SCANNERS READ CODES AND DATA STREAMS n TEST ACTUATORS n GRAPHING n LAB SCOPE n DVOM n TECHNICAL INFO

cbc GM PROM n CONTAINS SPECIFIC PROGRAMS SUCH AS; SPARK ADVANCE, FUEL INJECTION n SOME ARE ELECTRONICALLY ERASABLE n REPLACEABLE SEPARATE FROM PCM

cbc CODE CHART n SELF DIAGNOSTICS (SELF TEST MODE) n “HARD FAULTS” n “SOFT CODES” OR “MEMORY CODES” n ACCESS TROUBLE CODES WITH SCANNER OR BY MANUAL METHOD n ERASING FAULT CODES

cbc DATA LINK CONNECTOR’S (DLC)