Section 1 Essential Electrical Concepts - Autoshop 101

1 Electrical Circuit Diagnosis - Course 6231-1 Modern vehicles incorporate many Electrical and electronic componentsand systems: Audio Lights Navigation Engine control Transmission control Braking and traction controlYou need to know Essential Electrical Concepts to effectivelytroubleshoot these and other Electrical and electronic system troubleshooting can be straightforwardif .. You know what to look for. You know how to select and use the appropriate tools and the knowledge and techniques you will learn in this course, youwill be able to .. Diagnose and repair Electrical and electronic problems correctly onthe first attempt. Reduce diagnostic and repair time. Increase customer 1 Essential Electrical ConceptsIntroductionSection 11-2 TOYOTA Technical TrainingDifferent meters are used to measure voltage, current, and resistance: Voltmeter - to measure voltage Ammeter - to measure current Ohmmeter - to measure resistanceThese three metering functions are combined into a single tester calleda multimeter.

2 " Nearly all automotive technicians use multimeter is often called a volt-ohmmeter," even though mostmultimeters also measure amperes (current).A multimeter can be one of two types:1. Analog - display uses a needle to point to a measured value on a Digital - display shows measured value in actual numbers (digits).Metering FunctionsThree metering functions are combined ina typical digital 1-01TL623f100cMetersEssential Electrical ConceptsElectrical Circuit Diagnosis - Course 6231-3 Analog multimeters .. Use a mechanical movement to drive a pointer. Display a measured value where the pointer intersects a calibratedscale. Are not suitable for measurements in circuits with sensitiveelectronic components (such as ECUs). Are more susceptible to damage from mechanical shock than aredigital Analog MultimeterAnalog meters use a mechanicalmovement and are not suitable formeasurements in circuits with sensitiveelectronic 1-02TL623f102 AnalogMultimetersSection 11-4 TOYOTA Technical TrainingDigital multimeters.

3 Use a digital display. Display a measured value in actual numbers. Are suitable for measurements in circuits with sensitive electroniccomponents (such as ECUs). Are less susceptible to damage from mechanical shock than areanalog multimeters. Have a longer battery life. Have a higher internal DigitalMultimeterDigital multimeters displaythe actual measured valueand are suitable formeasurements in circuitswith sensitive 1-03TL623f103cDigital MultimetersEssential Electrical ConceptsElectrical Circuit Diagnosis - Course 6231-5 The main components found on the front panel of a typical digitalmultimeter (DMM) are .. Digital display Range selector Mode selector Input jacksDMMC omponentsThis figure shows themain components of atypical digital 1-04TL623f104cDMM ComponentsSection 11-6 TOYOTA Technical TrainingUse the mode selector to set the meter for the type of test to beperformed.

4 These are the modes available on a Fluke 87 DMM: Off - Turns the meter off. Turning the mode selector to any othersetting turns the meter on. Volts AC - Use to measure voltage in alternating current (AC)circuits. Volts DC - Use to measure voltage in direct current (DC) circuits. Millivolts DC (mV) DC - Use to measure very low voltage indirect current (DC) circuits. Resistance/Continuity (ohms) - Use to measure resistance andcheck continuity. Diode Check - Use to check the operation of a diode (meter sendsa small current through the diode). Amps or Milliamps AC/DC - Use to measure current in a circuit. Microamps (AC/DC) - Use to measure very small current in ModeSelectorThe mode selector knoblets you set the meter forthe type of test you wantto 1-05TL623f105 DMM ModeSelectorEssential Electrical ConceptsElectrical Circuit Diagnosis - Course 6231-7 DMMs display information that must be properly interpreted to get thecorrect measured DMM DisplaysThe digital display gives a direct readout inactual numbers.

5 However, you still mustproperly interpret the display to get thecorrect measurement 1-06TL623f106 Voltage type - The DMM shows the voltage type (AC or DC) in theupper right hand corner of the value - The large digits in the center of the displayrepresent the measured value. Typically, the total value will containfour or five digits with a decimal - To the right of the measured value number, the display showsletters that represent units:V voltsA amperes ohmsRange - The DMM displays the measurement range in the lower righthand corner of the display, just to the right of the bar DisplaySection 11-8 TOYOTA Technical TrainingUnit modifiers - The letters m, k, , and M modify unit values:Volts -mV millivoltsvolts x kilovoltsvolts x 1,000 Amperes -mA milliampsamps x Amicroampsamps x technicians rarely use readings at the microamp - ohmsk kilo-ohmsohms x 1,000M megohmsohms x 1,000,000 DMM Over-LimitDisplayThe or over-limit display appears wheneverthe test produces a valuethat exceeds the selectedrange.

6 For resistance,that typically indicates anopen 1-07TL623f107 Over-Limit Measurement - Most DMMs display an over-limit signwhen the meter is measuring voltage or current that exceeds the selectedor available Electrical ConceptsElectrical Circuit Diagnosis - Course 6231-9 Many DMMs offer a feature called auto-ranging." Meters with thisfeature allow you to disable it when you want to select ranges the meter is set to auto-range, it automatically selects the rangemost appropriate for the measurement being is convenient for making most measurements. It isespecially helpful when you do not know what value to expect. Aresistance measurement provides a good typical DMM has these ranges available for resistancemeasurements: 400 4 k /400 k 4 M If the DMM is connected to a component with an internal resistance ofabout 700 ohms, the meter can automatically select the 4 k.

7 Range. Withoutauto-ranging, you might scan through several ranges before determiningthat the 4 k range is most appropriate for this Auto-RangingDigital multimeters withauto-ranging willautomatically select theappropriate scale for atest 1-08TL623f108 DMM Auto-RangingEXAMPLES ection 11-10 TOYOTA Technical TrainingThe typical DMM has two test leads and four input jacks. The leadsplug in as follows: BLACK - always plugs into the COM input jack. RED - plugs into one of the three remaining jacks, depending onwhat measurement is being /diode input for measuring resistance, conductance, andcapacitance, as well as checking diodes (Voltage).- A input for measuring current up to 10 A/mA input for measuring current up to Input JacksThe meter leads must beplugged into the properinput jack for differenttests (voltage andresistance or two rangesof current).

8 Fig. 1-09TL623f109cDMM Test Leadsand Input JacksEssential Electrical ConceptsElectrical Circuit Diagnosis - Course 6231-11 Voltage is the electromotive force between two points in a you place the probes of a DMM on the terminals of a battery, youare measuring the electromotive force, or voltage, between the positiveand negative battery meter is connected tomeasure battery 1-10TL623f110cVoltageEXAMPLES ection 11-12 TOYOTA Technical TrainingApplications of voltage - Technicians are concerned with voltage indifferent applications: Source voltage Available voltage Voltage dropSource voltage - the battery supplies source voltage in mostautomotive Electrical voltage - use the DMM to measure voltage. Note thatvoltage measurements are made by placing the voltage leads in aparallel circuit to the circuit you are testing. (Parallel circuits arecovered in Section 2.)

9 Available voltage - is the voltage in a circuit available to operate drop - most parts of an Electrical circuit offers someresistance to current. Every element that has resistance causes avoltage drop. Voltage drop increases as resistance Electrical ConceptsElectrical Circuit Diagnosis - Course 6231-13 MeasuringVoltageThe meter leads in thisfigure show threedifferent ways tomeasure 1-11TL623f111cYou can measure voltage .. Between any two points in a circuit Between any point in a circuit and ground Across any component in the circuit- Switches- Relay contacts and coils- Connectors- Wires- CablesSection 11-14 TOYOTA Technical TrainingAvailable VoltageThe meter probes areplaced to test theavailable voltage atthe 1-12TL623f112cEssential Electrical ConceptsElectrical Circuit Diagnosis - Course 6231-15 Measure available voltage using a digital multimeter with these steps:1.

10 Set the mode selector switch to Volts Select the Auto-Range function or manually set the Because the battery supplies available voltage in automotivecircuits, you will typically measure voltages between zero and 12to 14 For Fluke Series 80 DMMs, set the range to For other DMMs, set the range to the value closest to and higherthan 12 Connect the voltmeter leads in parallel with the circuit element tobe Red lead closest to the battery (connect first).- Black lead to a good Read measurement on DMM Note Correctly apply meter leads are most likely reversed if the DMM display indicatesnegative polarity. It could also mean there is a fault in the 11-16 TOYOTA Technical TrainingVoltage DropVoltage drop indicatesthe voltage being used inthat Section of the 1-13TL623f113cVoltage drop is one of the most useful tests you can perform.