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COMPUTERS AND INPUT SENSORS Slide 2 cbc MICROCOMPUTER OPERATION HAPPENS IN STAGES Memory Slide 3 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 Slide 4 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 Slide 5 cbc BINARY CODE n A/D converter takes snapshot of analog signal n Computers only understand 1s and 0s. 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 Slide 6 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 Slide 7 cbc TYPES OF MEMORY n 3 DIFFERENT TYPES n READ ONLY MEMORY (ROM) n RANDOM ACCESS MEMORY (RAM) n KEEP ALIVE MEMORY (KAM) Slide 8 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 formulas used to perform calculations n Vehicle information: # of cylinders, valve size, transmission type, rear end Slide 9 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. Slide 10 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 Slide 11 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 Slide 12 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 Slide 13 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. Slide 14 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 Slide 15 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 Slide 16 cbc 3 WIRE SENSORS REFERENCE VOLTAGE SENSOR OR VOLTAGE MODIFIER n VOLTAGE REFERENCE n SIGNAL WIRE n SIGNAL RETURN (GROUND) Slide 17 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 Slide 18 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 Slide 19 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 Slide 20 cbc CYCLE DUTY CYCLE PULSE WIDTH FREQUENCY Slide 21 cbc PULSE WIDTH n LENGTH OF TIME IN MS, ACTUATOR IS ON n IE, DURATION OF ON-TIME n PULSE WIDTH MODULATION Slide 22 cbc VANE AIR FLOW METER n USES THREE TYPES OF VOLTAGE MODIFIERS SWITCH POTENTIOMETER THERMISTOR n MOVES DOOR TO DETERMINE AIR FLOW Slide 23 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 Slide 24 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 Slide 25 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 Slide 26 cbc 02 CROSSCOUNTS Generally, about 2 to 3 crosscounts is normal operation Slide 27 cbc ZIRCONIA SENSOR Slide 28 cbc TITANIA SENSOR Slide 29 cbc DIAGNOSTIC LOGIC TREE n LOGIC TREE OR DIAGNOSTIC CHART n SOME CHARTS INCLUDE EXPLANATIONS n MANY MANUFACTUERS USE THIS TYPE DIAGNOSTICS Slide 30 cbc LOOK UP TABLE USED TO DETERMINE BLOCK LEARN/INTERGRATOR Slide 31 cbc SCANNER n SCANNERS READ CODES AND DATA STREAMS n TEST ACTUATORS n GRAPHING n LAB SCOPE n DVOM n TECHNICAL INFO Slide 32 cbc GM PROM n CONTAINS SPECIFIC PROGRAMS SUCH AS; SPARK ADVANCE, FUEL INJECTION n SOME ARE ELECTRONICALLY ERASABLE n REPLACEABLE SEPARATE FROM PCM Slide 33 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 Slide 34 cbc DATA LINK CONNECTORS (DLC)