A6. A – General Electrical/Electronic System Diag
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Alternator
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a belt-driven generator that converts mechanical energy to electrical energy
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Amperage
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The flow of electrical energy
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Armature
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A part moved through a magnetic field to produce an electric current
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Battery
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A device that converts chemical energy into electrical energy
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Bearing
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A component that reduces friction between a stationary and rotating part, such as a shaft.
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Body Control Module (BCM)
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A component of the computerized self diagnosis system.
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Brake light switch
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A component of the braking system that completes an electrical circuit to illuminate the brake lights when the brake pedal is applied.
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Brush
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A conductive component that rides on the commutator or slip ring to provide an electrical circuit between rotating and stationary components.
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Bullhead connector
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a connector for wires that are to pass through the bulkhead of a vehicle
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Buzzer
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an electric sound generator that makes a buzzing noise
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capacitor
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an electrical device for the temporary storage of electricity, often used to reduce RFI
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Charge
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The passing of an electrical current through a battery to restore its energy
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Clock spring
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a device used on vehicles with airbags that allows a hard-wired circuit to be connected through a rotating steering wheel
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computer
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a component that receives inputs, performs calculations, and then sends outputs to load devices. Other names for the component include control module, controller, logic device, and electronic control unit.
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concealed headlights
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a headlamp system that retracts the lamps into the bodywork when they are turned off.
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continuity
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a complete path for electrical flow
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corrosion
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a chemical action that eats away material such as metal, paint, or wire.
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Courtesy lights
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lamps that illuminate the interior of a vehicle when a door is opened
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cruise control
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a device that automatically maintains vehicle speed over a wide range of terrain conditions.
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current
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the flow of electricity, measured in amperes
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current draw test
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a test to determine amperes required by the starter motor during starting operation
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digital
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an electrical signal having two states, on and off.
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electric fuel pump
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an electrical device used to draw fuel from the fuel tank and deliver it to the engine
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electronic ignition system
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an ignition system controlled by solid state electrical signals
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field coil
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a coil of insulated wire, usually wound around an iron core, through which current is passed to produce a magnetic field
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flywheel
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a heavy metal wheel that is attached to the crankshaft and rotates with it.
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fusible link
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a bar or wire that is designed to melt due to heat when a specified current passing through it is exceeded
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ground
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the path, generally the body of the vehicle, for the return of an electrical circuit. Also, a term used for causing an accidental or intentional short circuit
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harness
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a group of electrical conductors
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headlamps
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the lamps at the front of a vehicle to provide illumination for the road ahead.
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High Intensity Discharge (HID)
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a type of headlight that uses high voltage levels to create a very intense light
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Horn relay
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an electromagnetic device used to activate the horn when the horn switch is closed
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Hydrometer
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an instrument used to measure the specific gravity of a liquid.
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Ignition switch
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the main power switch, generally key operate, of a vehicle
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Inertia switch
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A switch found in the fuel pump circuit to turn off the fuel pump. and other vehicle accessories, in the event of a collision
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Intermittent
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an event that only happens part of the time
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Light Emitting Diode (LED)
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An electronic device that creates light when a voltage is applied to the anode and ground is connected to the cathode. LEDs are widely used on vehicles instead of incandescent bulbs because they draw less current and last longer
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Linkage
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levers or rods used to transmit power for one part to another
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Load
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A device connected to an electrical circuit to provide resistance and/or control the current flow.
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Load test
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An electrical test for motors and batteries in which current draw and voltage is measured
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Logic device
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A component that receives inputs, performs calculations, and then sends outputs to load devices. Also referred to as a computer.
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Module
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A control assembly designed to perform one or more specific tasks
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Ohm
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a unit of measure of electrical resistance
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On-Board Computer
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The resident or main computer in a vehicle
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Open circuit
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an incomplete electrical circuit
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Power steering pump
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A hydraulic pump used to provide a fluid boost for ease in vehicle steering
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Printed Circuit
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Electrically conductive circuit paths generally etched on rigid or flexible strata
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Printed circuit board
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an insulated board on which a printed circuit is etched
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Resistance
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The opposition to electrical flow.
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Schematic
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a drawing of a system using symbols to represent components.
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Sending unit
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An electrical or mechanical sensing device to transmit certain conditions to a remote meter or gauge.
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Series
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a part of an electrical circuit whereby one component is connected to another, as negative to positive, and so on
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Servo
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a device that converts hydraulic pressure to mechanical movement
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Short circuit
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The intentional or unintentional grounding of an electrical circuit
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Shunt
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A parallel electrical connection or circuit
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Solenoid
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A device that uses electromagnetism to create linear movement
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Speed sensor
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an electrical device that senses the speed of a rotating shaft or vibrating member
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squeal
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a continuous high pitched noise
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Starter
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The electric motor and drive used to start a vehicle engine.
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Starter solenoid
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A magnetic switch used to engage the starter for starting an engine
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switch
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a mechanical device used to open and close an electrical circuit
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Transmission
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a device used to couple a motor to a mechanical mechanism
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Troubleshoot
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To determine the problem, the cause of the problem, and the solution by systematic reasoning
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Turn signal
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lights on the four corners of a vehicle to signal a turn
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Voltage
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electrical pressure. Also known as electromotive force
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Wiper
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A mechanical arm that moves back and forth over the windshield to remove water
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a voltmeter may be connected
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across a component In a circuit to measure the voltage drop across the component.
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what must be flowing through the circuit during the voltage drop test?
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current
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The amount of voltage drop depends on the..
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resistance in the component and the amount of current flow the component requires.
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In a normal electrical circuit, the electrical load should drop...
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most of the voltage; and the wires, connectors, switches, and relays should drop very little voltage.
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What is a good way to determine whether wires, connectors, switches and relays are operating correctly?
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perform a voltage drop test while the circuit is energized.
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An ammeter has low internal resistance so that it can...
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measure current through it.
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in order for an ammeter to measure current going through a circuit it must be connected...
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in series with a circuit
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ammeters measure the current flow from the ...
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strength of the magnetic field surrounding the wire.
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High current flow is caused by
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high voltage or low resistance
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an ammeter comes in handy for many types of diagnosis since ..
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current is the supply to get any electrical job done.
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list the three examples of things a technician would use an ammeter to measure
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1. Generator/Alternator 2. Battery 3. High-power circuits
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Why use an ammeter on a generator/Alternator?
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The vehicles charging system is the power station for everything electrical. Generators are matched to the total load the vehicle might generate so that it can maintain adequate voltage, while supplying enough current. Technicians use an ammeter, usually in conjunction with a voltmeter, to measure the ability of the generator to meet its intended output specification.
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Why use an ammeter on the battery?
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The battery stores current as potential under a certain pressure (voltage). An ammeter is used, usually in conjunction with a voltmeter, to measure the potential of the battery when it is working to see whether it meets its intended load specification
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Why use an ammeter on a high-power circuit?
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Electric fuel pumps, HVAC blower motors, starters, electric cooling fans, window motors, solenoids, and any other high load item can be tested in the same way to determine whether they require more current than they were designed to. NEXT PAGE ---->
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An ohmmeter has an internal power source. Meter damage may result if it is connected to a ..
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live circuit
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Most currently produced ohm meters are auto ranging (automatically selecting the proper resistance range). If not be sure to select the proper range when measuring a circuit. For example, when a component has a resistance of 10,000 ohms select the...
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X10000 or 10K range
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Why can an ohmmeter come in handy?
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because some circuit components have published resistance specs
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give examples of items that often have specifications for resistance, which if used can be a good way to determine whether a component has a problem.
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Fuel injectors, solenoids, and sensors
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An oscilloscope ...
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converts electrical signals into visual image representing voltage changes over a specified period of time.
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using an oscilloscope, an upward movement of the trace means the...
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voltage has increased, whereas a downward movement means the voltage has decreased. If the trace stays flat, the voltage is staying at that level. As the trace moves across the screen of the oscilloscope, time is represented.
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The size and the clarity of the trace on an oscilloscope is dependent on the ...
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voltage scale and the time reference selected by the technician.
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Most oscilloscopes are equipped with controls that allow...
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voltage and time interval selection.
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Analog scopes show the..
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actual activity of a circuit and are referred to as \"real-time\" scopes.
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Digital scopes...
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convert the voltage signals into digital signals; therefore, some delay between the electrical activity and the display is experienced. This delay does give the trace a cleaner appearance, as an analog trace is clean only when the voltage has been constant for some time
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a scan tool is designed to
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communicate with the vehicles computer
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Connected to the computer through a diagnostic connector, a scan tool can access ...
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live data and trouble codes as well as run tests to check system operations
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Bidirectional communication is when...
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scan tools have the ability to set up special functions within the vehicles computer systems that help a technician test circuits or to activate them so that a technician can watch the scan tool data for changes.
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Many of the electronic systems of late model vehicles can be accessed and even exercised by the...
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scan tool
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The data displayed on a scan tool should be compared to the...
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expected or known good data tables given in the service manual for the vehicle being tested.
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Depending on the year of the vehicle and the system with which it is equipped, the trouble codes displayed on the scan tool may indicate a ...
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general problem area or may indicate a specific part of a circuit
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Observing the activity of various inputs and outputs can lead a tech to problems that may be related or unrelated to the...
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computer system.
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DTCs are a function of most of the...
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control modules on late-model vehicles.
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Each control module is equipped with diagnostic software that will record a...
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DTC when a problem is present for a short period of time. The tech can retrieve the DTC and then follow a diagnostic routine to find out what caused the DTC. After the repair is made, the DTC should be cleared from the memory of the control module with the scan tool.
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name the 4 various circuit problems that can occur in electrical circuits
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short circuit high resistance circuit grounded circuit open circuit
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a short circuit is when the ...
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electrical path is changed
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all circuits are designed to be routed through the various components such as
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wires, switches, fuses, relays , motors, lights, and heat strips
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a short circuit happens when..
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the electrical flow takes an unwanted path.
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what is the preferred tool to locate short circuits?
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voltmeter
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high resistance circuits are circuits that have ...
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high resistance as a result of corrosion, loose terminals, and burnt contacts. these circuits will have reduced current flow, and the electrical components will not function properly
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circuits that have high resistance as a result of corrosion, loose terminals, and burnt contacts can be found by using...
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either an ohmmeter or a voltmeter.
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The ohmmeter is connected ____________ with the part of the circuit that needs to be tested
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in parallel with the circuit turned off
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The voltmeter is connected ____________ with the part of the circuit that needs to be tested
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in parallel while the power is turned on
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a grounded circuit is sometimes called a..
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short to ground
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if an electrical circuit gets a short to ground on the power side of the circuit, the...
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current flow will rapidly increase and probably open the circuit protection device.
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if a short to ground happens on the ground side of the circuit, the...
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circuit will not be changed.
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if a short to ground happens on the ground side of the circuit, the circuit will not be changed. the exception to this example would be if the circuit is..
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switched on the ground side, in. this case the circuit would operate all of the time.
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the best tool to locate grounded circuits is..
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an ohmmeter
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open circuit does not allow...
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current to flow.
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an open circuit will not open any...
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circuit protection device.
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to locate open circuit what tool(s) can be used?
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ohmmeter or voltmeter
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an open circuit will have how much resistance?
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infinite.
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The voltmeter will measure what and where on an open circuit?
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it will measure source voltage at all test points before the open circuit and zero volts at all test points after the open circuit
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the voltmeter will measure source voltage at all test points _______ the open circuit and zero volts at all test points ______ the open circuit
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the voltmeter will measure source voltage at all test points before the open circuit and zero volts at all test points after the open circuit
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what can be used to bypass a part of a circuit to locate a defect in the circuit?
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a jumper wire
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if wiring is suspect, a supply can be brought to a component with ____________ to see whether it operates correctly
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jumper wires
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besides supplying power to motors and lights, jumper wires can bypass...
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switches, relays, and solenoids
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besides supplying power to motors, lights, switches, relays, and solenoids, jumper wires can also be used in some diagnostic routines to remove...
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a component from a circuit to test for high resistance.
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a jumper wire should never be used to
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check circuits that are associated with computers, a high impendance voltmeter should be used for checking circuits associated with computers
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for checking circuits associated with computers what must be used
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a high impedance voltmeter
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a parasitic draw occurs when...
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a component stays on after it should shut off or when a component that should stay on begins to demand excessive current
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name examples of systems that may cause a parasitic draw (stay active for quite some time after the vehicle is turned off)
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alarm systems, on board diagnostics (OBD) II evaporative systems, power train control modules (PCMs), clock and radio memory, and convenience lighting
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name some very common causes of parasitic drain that can kill the battery over a few hours or a few days.
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light switches, relays, and generator voltage regulators often these problems are intermittent and require good diagnostic skills to locate.
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many car manufacturers recommend measuring battery drain with a ...
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tester switch connected in series at the negative battery terminal. known as a drain test
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explain how to perform a drain test
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A multi-meter with a milliamperes scale is connected in parallel to the tester switch. when the tester switch is open, any current drain from the battery must flow through the mult-meter
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when performing a drain test some computers require several minutes after the ignition switch is turned off before they enter sleep mode with a reduced current drain. Therefore...
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after the ignition switch is turned off and the tester switch is opened, wait for the specified time before recording the milliamp reading.
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for a drain test, the maximum specification is typically no more than ...
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35 to 50 millamps
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when an ohmmeter is connected to a circuit breaker, fuse, or fuse link, the meter should read...
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zero ohms if the component is working properly.
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an open circuit breaker, fuse, or fuse link causes what kind of reading
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Infinite ohmmeter reading
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the current flow from an ohmmeter will not cause an automotive ___________ to open
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circuit breaker
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a good fuse will cause a test light to what
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illuminate on both the output and input side of the fuse
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a blown fuse will only illuminate on
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only the input side of the fuse
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a fuse that will not light up on either the input or output side is...
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not receiving electrical power and cannot be tested this way
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what can be used to test a diode?
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a dmm
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how do u check a diode with a dmm
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turn the dial to diode test and then touch the test leads to the diode and note the reading on the meter. the test leads then should be reversed and then reconnected to the diode.
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a good diode will...
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have a small voltage reading when connected one way and will have an out of limits (OL) reading when connected in reverse polarity
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when viewing wiring schematics power (B ) comes from...
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the top of the page
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when viewing wiring schematics ground (negative) comes from...
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the bottom of the page
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when viewing wiring schematics wire colors are represented by
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letters next to the wires
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when viewing wiring schematics circuit numbers are represented by
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numbers next to the wires
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when viewing wiring schematics universal symbols for fuses, switches, relays, motors, resistors, an connectors, are used to show ...
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the circuit layout
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when viewing wiring schematics it is good diagnostic practice to ...
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trace the flow of electricity in order to understand how the circuit works and then decide where to start the diagnosis
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late model vehicles typically have several on-board computers, which requires them to have a network that allows the computers to communicate with each other. this network also slows for scan tool communications. typically, this network consists of...
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two wires that are connected to the various modules and the data connector in parallel.
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the process of pulsing voltage to send signals is called ...
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multiplexing or bussing
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the bus network wires are twisted continuously in order to ...
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help resist radio frequency interference (RFI) and electromagnetic interference (EMI) from entering the system.
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the bus network wires are twisted continuously in order to help resist radio frequency interference (RFI) and electromagnetic interference (EMI) from entering the system. this method of sharing data among modules helps to...
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eliminate redundant wiring to the modules that need the same sensor information.
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most late model vehicles will have more than one data network on board. these networks vary in the speed at which data is transmitted from one module to another. the fastest network is called...
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CAN, which stands for Controller Area Network.
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CAN (controller area network) is a twisted pair of wires that can transmit at speeds up to...
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one million bits per second.
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most high speed network such as CAN use resistors at each end called..
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terminating resistors
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most high speed network such as CAN use resistors at each end called terminating resistors, which are used to help...
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reduce interference of the network.
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most high speed network such as CAN use resistors at each end called terminating. resistors which help reduce interference on the network. A technician can test to see whether these resistors are correct by measuring at the...
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DLC pins 6 and 14 with the ignition switch turned off
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most high speed network such as CAN use resistors at each end called terminating. resistors which help reduce interference on the network. A technician can test to see whether these resistors are correct by measuring at the DLC pins 6 and 14 with the ignition switch turned off. The correct value of this reading should be...
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60 ohms.
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problems that can occur in the bus communication are
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opens, shorts, and unwanted resistance.
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problems that can occur in the bus communication are opens, shorts, and unwanted resistance. diagnosing these problems involves using the...
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DMM in conjunction with a diagnostic trouble chart.
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problems that can occur in the bus communication are opens, shorts, and unwanted resistance. diagnosing these problems involves using the dmm in conjunction with a diagnostic trouble chart. The scan tool becomes less valuable when a communication problem occurs because..
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it wil not be able to receive data in the event of a wire failure.
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another way to check for activity on the data bus network is to connect an...
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another way to check for activity on the data bus network is to connect an oscilloscope to the network and monitor rapid voltage activity.
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another way to check for activity on the data bus network is to connect an oscilloscope to the network and monitor rapid voltage activity. If the voltage levels are changing continuously while the key is on, then it is probable that ...
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it's probable that some communication is taking place on the data bus.
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While diagnosing failures in the data bus communications network, name the two potential locations of poor conductors
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The DLC connector on the vehicle as well as the scan tool wiring lead are potential locations of poor conductors.
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Prior to replacing any control module, the technician should perform...
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careful diagnosis of the system in question.
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Prior to replacing any control module, the technician should perform careful diagnosis of the system in question. Items that need to be checked include the...
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battery and charging system performance, connector quality and tightness, and the supply of good power and ground to the control module.
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what are some recommended procedures during a control module replacement
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it is good practice to remove the negative battery cable before disconnecting the control module. it is also recommended for the tech to touch a metal surface of the vehicle to discharge any electro static charge that may be present. Some manufacturers recommend wearing a grounding strap during a control module replacement .
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when installing a control module the tech should..
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make sure that all connectors are securely connected. it is also advisable to reinstall all of the hold-down fasteners for the module in order to prevent excess movement when the vehicle is operated.
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after a control module is installed what is the next step in the process on many late-model vehicles
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many late-model vehicles must be programmed after the hardware is installed.
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what are the two things needed in order for a tech to reprogram a control module?
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programming tool or scan tool that has a programming function to perform this action. In addition, a module programming database is needed to retrieve the correct program to upload to the new module
