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elec13 Electrical Diagnostic Tools.pdf

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ELEC13 ELECTRICAL DIAGNOSTIC TOOLS
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Body Electrical Diagnosis - Course L652 1 1. Explainwhattolookforwhenmakingavisualinspection. 2. Showthepropertechniquesforusingajumperwire. 3. ExplaintheadvantagesandfeaturesofDigitalMultimeters. 4. Explainhowtouseavoltmetertomakeopencircuitandvoltage dropmeasurements. 5. Explainhowtouseadigitalammeter,bothseriesandinductive types. 6. Explainhowtouseadigitalohmmeterforresistance,continuity, anddiodechecks. 7. Performon-carworksheetsusingallofthefunctionsoftheDVOM. Section 3 Electrical Diagnostic Tools Learning Objectives:Section 3 2 LEXUS Technical TrainingElectrical Diagnostic Tools Body Electrical Diagnosis - Course L652 3 AfterlookingataproblemcircuitontheEWD,youwillneedto determineifdifferentcomponents,connections,orwiresareOKby makinganon-carinspection.Therearefivecircuitinspectiontoolsthat willbecoveredinthissection: w Visual w JumperWires w DigitalMultimeter w Voltmeter w Ammeter w Ohmmeter Animportantpartofanydiagnosticprocedureisto makeavisual inspectionofthevehicle.Avisualinspectioncanquicklycatchthe simpleproblemswhichmayberelatedtothecustomer’scomplaint. Readthe EWDsystemoutline tofindout howthecircuitissupposed tooperate .Thenoperatethecircuitanddetermineexactlywhatisand whatisnotworking. Thisinformationcansavealotoftime.WiththehelpoftheEWD,you cannarrowdown onpaper theareasyouwillneedtoinspectfirst.By tracingthepathsofcurrentflowonthepartsofthecircuitthatwork, youcaneliminateareasofthecircuitthat arenot causingtheproblem. EWD System Outline Read the System Outline to find out how the circuit is supposed to work. Then thoroughly test the circuit, operating as many features/functions as possible. Introduction Visual Inspection Operate the Circuit ThoroughlySection 3 4 LEXUS Technical Training Connectorproblemsareoneofthemostfrequentcausesofelectrical problems.Typicalproblemsinclude: w Connectorsnotlocked“ w Terminalsbackedout/notseated w Corrosionormoisture w Excessiveterminalspread Thisproblemisoneofthemostdifficulttodetect,especiallywhenthe femaleterminalmatesdirectlytoacomponentorECU.Tocheckthe fit“ofthefemaleterminalyoucaneitheruseanewmaleterminal fromthe LexusWireHarnessRepairKit orusethe LexusTerminal TensionGaugeSST . Whendiagnosingthecauseofanintermittentproblem,makeyour inspections strategically.Keepinmindthatdisconnectingconnectorsor movingthepositionofwiresandharnessescancausetheproblemto temporarilyfix“itself.Thereisnomagic“toelectricity;besureto isolateandrepairthecauseoftheproblem. Terminal Problems Typical terminal problems include a poor crimp of the wire to a terminal, and terminal tension or spread. The terminal can be checked using the Terminal Tension Gauge SST. If the contact at the terminal is loose, you can be fooled when you backprobe the terminal at the component—the voltmeter reads voltage, but the pin isn’t feeding it to the component. Checking Connectors itDOESNOTtellyouhow much resistancethereisintheconnectionorcircuit. Measuring Open Circuit Voltage This inspection can be made by backprobing the terminal, or from the front with the connector disconnected. If you have to probe from the front of the connector, NEVER insert the test probe into a female terminal. Digital Voltmeter Measuring Open Circuit Voltage or Pin Voltage HINTSection 3 10 LEXUS Technical Training A voltagedrop measurementistaken dynamicallywhilethecircuitis inoperation. 1. Turnthecircuit ON. 2. Connectthepositiveandnegativeprobesofthemeterinparallelto thecomponentorsectionofthecircuityouwanttocheck. w ByusingtheEWD,youcanisolateportionsofthecircuitandcheck forunwantedresistances. w Ameasurementof0Voltscanindicatetwodifferentconditions: a. Thereisvirtuallynoresistanceinthepartofthecircuityouare checking. b. ThecircuitisOFForopen;nocurrentflow. Thisisthemostaccuratewaytodetectaproblemresistanceinhigh amperage(above3or4amps)circuits.Inthesecircuits,evena resistanceof1 W orlesscanhaveabigeffectontheload.Becausethe testisdonewhilethecircuitisoperating,factorssuchastheamountof currentflowandtheheatgeneratedwillbetakenintoaccount. Measuring Voltage Drop Connect the voltmeter in parallel to the part of the circuit you want to check by backprobing the connector. Remember the load should be getting about the same as battery voltage WHILE THE CIRCUIT IS OPERATING. Voltage Drop Measurement HINTElectrical Diagnostic Tools Body Electrical Diagnosis - Course L652 11 BecauseRepairManualandEWDspecificationsareusuallyinvolts, theammeterisnotfrequentlyusedasatoolinbodyelectrical diagnosis.Itcan,however,beaveryeffectivetool. Theammeteristypicallyusedin: 1. StartingandChargingSystem inspection 2. Diagnosingparasiticloadproblems. A parasiticload is sometimesreferredtoasadraw“,somethingthatdrainsthe batterywhilethecarisparkedovernight. Theammetercanbeusedtodynamicallytesttheconditionofacircuit. ButbecauseamperagespecsarenotfoundintheRMorEWDformost circuits,andbecauseammeterscannotpinpointthelocationofaproblem likeavoltmetercan,itisnotfrequentlyusedinbodyelectricaldiagnosis. Ifacomponentinacircuitisparticularlydifficulttoaccess(suchasthe electricfuelpump),anamperagemeasurementofthecircuitcanbea goodindicatorofthecircuit’scondition.Becausetherearenospecs givenforthiscircuit,youwillneedto measuretheamperagedraw ofthesamecircuitonaknowngoodvehicle ,and comparethe readingstodetermineifyouhaveaproblem. Diagnosing with an Ammeter For the fuel pump, an ammeter can be put in series at the +B and Fp terminal (key ON, engine OFF). This operates the fuel pump and lets you check the amount of amperage the fuel pump is drawing. Compare this reading to a known good vehicle. Digital Ammeter HINTSection 3 12 LEXUS Technical Training Therearetwotypesofammeters:a seriestype and clamptype . A seriestypeammeter isthetypeofmeterthatisbuiltintoevery DVOM.Thismeterisdesignedtomeasurerelativelysmallcurrent flows(below10A).Mostmetersmeasureineither milliamps(mA) or Amps (A).Beforeconnectingthemeterintothecircuit,makesurethe circuitdrawiswithinwhatyourmetercanhandle.Itisagoodpractice toinitiallysetthemetertothehighestrangeavailable,andlowerthe rangewhilethecurrentisbeingmeasured.Mostammetersarefuse protectedtopreventdamagefromshort-to-groundsoroverload conditions.Theseriestypeammeterisbestsuitedformeasuring currentflowsbelow1A. Wehavebeenusing clamptypeammeters foryearsonstarting/ chargingsystemtesterssuchastheSunVAT-40/60.Thistypeof ammeterisalsoavailableasanaccessorythatyoucanusewithany DVOM.Thesebattery-poweredclamptypeammeters(sometimes referredtoasinductive-type“ammeters)measurecurrentflowby sensingthestrengthofthemagneticfieldproducedaroundthewire whilecurrentflowispresent.Theseclampsthenconvertthisamperage readingintoa voltagewhichisreadwiththe DVOMsettomeasure millivolts.Duetoalackofaccuracybelow1amp,theseaccessoriesare bestsuitedforanyamperagemeasurementexceptnormalparasiticloads. Itcanbeusedtotroubleshootahighparasiticloadproblemifthedraw“ isabove0.5A,dependingonthemodelofampclamp“youareusing. ThecorrectconnectionsforeachtypeofammeterareshowninFigure3-10. Series and Inductive Ammeters Series ammeters require the circuit to be “disconnected” in order to connect the ammeter. Inductive ammeters simply attach around the wire, but cannot measure low readings. Types of Digital Ammeter
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