HET 4 ELECTRICAL Flashcards
ELECTRICAL REVIEW AND NEW
When finding electrical faults where should a tech look first?
Source - confirm voltage and connection
How often should wiring be secured?
1.8m or 6Ft
What size gauge of wire should be used when doing repairs?
OEM gauge
What is the component called on a relay from point 85 to 86?
Actuator winding
In a Parallel circuit what should total resistance be?
Less than the smallest resistance
In Series circuit how can you find total resistance?
The sum of all resistance
What are the two most common electrical faults?
Open or High Resistance
What does MALT stand for?
Material
Area
Length
Temperature
What effect can too long of wires have on a system?
Increase resistance
What are the two types of grounds?
Chassis ground (frame)
or
Dedicated ground
Can ALL circuits be soldered for repairs?
No, solder is not recommended on digital circuits
What are some type of repairs for wiring?
Western union splice
crimp with Butt connector
crimp with Splice connector
solder all
How much insulation should be removed when doing crimp style wire repairs?
5/16” or 7.5mm
190404b pg16
Is series or parallel circuits the most common for lighting circuits?
Parallel
Why should you let circuits warm up before testing?
It can affect your reading
Operator complains that the light is not as bright as usual. The tech finds source voltage drop across the light. Is the operators complaint valid?
No, that is as bright as it will be with source voltage
If you have a dim light, what could be the problem?
A high resistance on ground or power side
What should be done to the system before taking resistance readings on a system?
De-energize the circuit or remove component
What does a high impedance DMM have for resistance?
10 Mega Ohms
Ohm’s law dictates?
that one volt of electrical force is required to cause one ampere of current to flow through one ohm of resistance
In a parallel circuit what should be the voltage available through all legs of the system?
Source voltage (or the same)
What is troubleshooting to find electric faults also referred to?
Isolating the fault (failure)
When trying to diagnose an electrical fault, using your DMM it is okay to pierce the insulation on the wiring to find the failure?
No. DO NOT piece the insulation
ALWAYS connect the probes of the DMM at accessible conductor connections
To join multi-strand wire, how much insulation should be removed. (Not a crimp style repair)
20mm or 3/4”
190404b pg 12
How are electrical schematics drawn?
De-energized and normal position
What is the purpose of a relay?
To use a small amount of amps to control a LARGE amount of amps
Why do we use relays?
To allow a smaller gauge wire
Do electrical schematics show exact location of components?
No
When repairing or connecting different gauge wires or multiple wires, what should be used?
A splice clip crimp
Voltage can be shown as (E), why?
Stands for Electromotive force
Where can high resistance be found in a wire harness that has weather pack or deutsch connectors?
At the connector, if it is corroded or not mated correctly
What can be used to help keep connections clean and moisture free?
O-ring seals, dielectric grease or siealant silicon can be used
What do manufactures publish to guide the tech through trouble shooting faults?
Flow charts
If a component is not working at all what is the probable fault?
Open
If two components work at the same time when the operator only turns ONE on what is the probable fault?
A short (shot to voltage)
What is the reason for headlight adjustment?
To provide max illumination or provide proper night time views without causing oncoming driver discomfort
What is the last step in preparing to do a headlight adjustment?
Shut down the engine, set parking brakes and chock the tires
What are the two movements available when adjusting headlamps?
Vertically and laterally
Can the headlamps be adjusted on a truck that isn’t level?
No, the headlamps will have the most accurate adjustment when the vehicle is level
Why should the suspension be checked before aligning head lights?
A sagging suspension can create an unlevel truck
What are the gauge types available?
LED LCD Mechanical Analog Electric Analog Vacuum fluorescent information
Does cold temperatures affect Liquid Crystal Displays?
Yes
What are you allowed when testing specific gravity variance between highest and lowest cells specific gravity on batteries?
a) 5
b) .5
c) 0.05
d) 0.0005
0.05 (half)
What bias is needed to provide light from LED?
Forward bias
Do you need back lights in an LED gauge?
No the LED gives off the light needed
Does LCD gauges need a back lamp available?
Yes or you cannot read the gauge in the dark
What do the numbers/letters look like in a vacuum fluorescent display?
Pixels, tiny dots of light
Do vacuum fluorescent gauges need to be illuminated from behind?
No
What does multiplexing reduce?
Complexity, Cost, Weight, and Size of wiring harness
What are the common communication data buses?
J-1708/1587 AND J-1939
What do modules do with inputs and outputs?
Receive Inputs
and
Control Outputs
What are some circuits that for safety are on constant power?
Headlamps Tail lamps brake lights clearance/marker lights cab/sleeper lights electric horn 7 PIN trailer receptacle ignition switch
What are the two types of common circuit breaks?
Type I - auto reset (cycling)
Type II - manual reset/repair
Describe the third type of circuit breaker
Type III - push button type
What size fusible link should be used?
4 gauge size Smaller than what it is protecting
ie. on an 8 gauge wired circuit, use a 12 gauge fusible link
In a light circuit with a Type I circuit breaker, what could be causing a “flashing” light?
A short to ground, allowing a higher than normal current causing the circuit breaker to open
How many volts are lowered with the terminal block in the daytime running light circuit?
2 or 3 volts
What does a terminal block need due to heat created by lowering voltage?
Aluminium heat sink
The daytime running light terminal block can be referred to as?
a module
When can Night running lights be used?
When the high beams are ON
What colours are clearance/marker lights?
Amber or Red depending on location
What is used in the dash panel lights to control the light intensity? (2 options)
Series connected rheostat
PWM - Digital signal
What should a tech be caution about when mounting a rheostat in a system?
Creates heat when reducing system voltage
Constant power terminal can also be called?
Powered at all times terminal
If there is damage to the cladding sheath on a optic fibres, what is the repair?
Cannot be repaired, must be replaced
In a system with LEDs can electromechanical flashers be used?
No, there isn’t enough current draw
What controls a vehicles back up lights?
Transmission-mounted switch
or
ECU
Describe Solenoid
An electromagnetic device - changes electrical energy into linear movement
What are the three categories of solenoids?
Discrete
Proportional
Latching
Does the return spring in a discrete solenoid hold the plunger in a relaxed position or in a fully extended position?
Relaxed
What are the two positions of a discrete solenoid?
Fully Retracted
or
Fully Extended
What could result if the sleep door is left unlatched for a long period of time? (uses a discrete solenoid)
It could overheat and melt insulation
Making the solenoid useless
A proportional solenoid has how many positions?
infinite
If the voltage increases in a proportional solenoid what happens to the magnetic field?
Also INCREASES
What controls the voltage signal to a proportional solenoid?
ECU
What controls a latching solenoid?
Current-reversing circuit
Describe self-induction
Producing a voltage in the coil circuit when current flow stops
How can switch contact arcing be prevented?
Install a high value resistor in parallel with the solenoid coil
or
Clamping diode (self-discharge diode)
What does a DC motor use to produce a rotary mechanical motion?
Electricity and magnetism
A conductor that is bent into a U shape is also called?
An Armature
in a DC motor what do the stationary brushes that contact the split rings connect to?
Cables to a battery
A device that produces electricity from rotary mechanical motion is a?
Generator
The voltage that a dc motor produces is called a?
Counter Electromotive Force (CEMF)
If you reverse polarity in a PM motor, what will happen?
Reverse the direction of rotation
A shunt motor can be referred to as?
Parallel wound direct current motor
True or False
A shunt motor can regulate its own speed?
TRUE
Where are parallel wound direct current motors used?
Fan Blower Motor
-Where uniform speed and low starting torque are wanted
Field wound motors can change direction of rotation with no special features?
NO you need to add extra switches and make internal motor wiring connections
What must be done to a DC motor to reduce speed?
Resistors connected in series
If a DC motor has two shunt windings, one high resistance and one low, how many speed options can be made?
High, Medium and Low
If a component is on 100% of the time what is its duty cycle?
100% duty cycle
If a component is off 20% of the time what is its duty cycle?
80% duty cycle
How many ways can cruise control be shut off, as per CMVSA?
Truck Braking, Clutch Position and dash mounted switch
in an auto trans vehicle there might only be two
What does a battery isolation switch help prevent?
Discharging of the battery while the truck is parked
What must a tech do when bypassing the battery isolation switch?
Install fuses on both the negative and positive leads to protect the wiring harness
What can be used to reduce or eliminate interference or static noise?
Install a series coil (filter choke) OR
parallel-connected capacitor
Do permanent magnet direct current motors provide constant or variable torque?
Constant torque
What are the electromagnets that supply the magnetic field called?
Field Coils
The iron core the field coils are wound around is called?
Pole Shoes
How are turn signal flashers connected into the turn signal light circuit?
In Series connection
List the three types of Solenoids
Discrete
Proportional
Latching
What makes the latching solenoid very different from the other two solenoid types?
The latching solenoid does not return to its normal state by spring pressure. The magnets hold it to one position or the other
What does solenoid do with the electrical energy sent to it?
Make it into Linear Movement
How many positions are available on a discrete solenoid?
Only TWO (2)
True or False
A discrete solenoid works well with long periods of operation.
False
How many positions does a proportional solenoid have?
Inifinite
What allows a proportional solenoid to be used continuously?
Fine diameter copper windings
True or False
Solenoids need non-permeable cases
True
What is used to prevent self induction on a solenoid?
High value resistor in parallel or clamping diode (self-discharge diode)
What does a Direct Current motor use to produce rotary mechanical motion?
Electricity and magnetism
CEMF stands for?
Counter Electromotive force
If a field wound DC motor has too much mechanical resistance what will happen?
High Current creates high heat and can burn out circuit
When replacing a DC motor what should the technician be aware of?
Motor must be the correct size to give the correct speed
In a DC motor what is used in the circuit to avoid the generation of voltage?
Blocking diode
Electricity takes what path?
a) path of most resistance
b) path of least resistance
Path of least resistance
Why are permanent DC motors favorable?
Low Maintenance
Reliable
Constant torque
High-load application
A permanent magnet DC motor uses what to limit speed?
CEMF and load on the motor
How is rotation reversed on a PM DC motor?
Reverse polarity to the armature
True or False
Parallel wound DC motors can regulate their own speed?
True
What are the three ways to control DC motor speed?
Variable electrical resistance
Multiple shunt windings
PWM
Indirect gauges can receive a signal in two ways, what are the two signal types?
Analog
OR
Digital
How are direct acting gauges connected to the component they are monitoring?
connected directly to source
What are three tyoes of analog gauges?
Balancing coil gauge
Stepper motor gauge
Air core Gauge
ICU stands for?
Instrument control unit
What is in a stepper motor gauge that allows it to generate a PWM?
Microprocessor
What is used to make ONE step into many MICRO steps?
a gear reduction
Indirectly operated electrical gauges require WHAT to transmit a signal to the dash mounted gauge?
Sending units
True or False
A positive type coefficient thermistor’s resistance increase as temperature increases
TRUE
What happens to resistance in a negative type coefficient thermistor as temperature increases?
Decreases
A thermistor is what kind of resistor?
Variable - to temperature
Anti-Slosh Module helps with what?
Minimizes the gauge pointer fluctuation as liquid moves around in tank
True or False
A fuel level sending unit does not need calibration
False, may need calibration before or after install
What gauges can determine the condition of the trucks electrical system?
ammeter and voltmeter
Why are fuses used in dash circuits?
to avoid dash fires
A shunt ammeter uses heavy gauge cable or light gauge cables between the alternator and the battery?
Heavy gauge cable
With a shunt ammeter what is now possible?
cables to the dash gauge can be small gauge
Dash Digital ammeters use what? (2 things)
hall effect sensor
intergrated circuit amplifier
When the alternator is not producing what will the gauge show?
Negative - showing the discharge
Speedometers indicate what?
vehicle speed in Km\h or MPH
What are the two speed sensor options on a transmission output shaft?
Rotating permanent magnet or Stationary permanent magnet
SAE stands for?
Society of automotive engineers
What does SAE do for electronic control systems?
Develop and set the standards
Backbone is also referred to as?
data bus
Nodes have what kind of addresses?
Unique address
DIP stands for?
Dual in-line package
What must be calculated before calibrating the speedometer?
Pulse per mile (PPM)
The DIP switch’s purpose is what when the speedometer directly receives the speed signal from the speed sensor?
Calibrate electronic speedometers
PPM is found with what information?
M - tire revolutions per mile
Ra - rear axle ration
N - number of chopper teeth on tone ring
How many chopper teeth on a tone ring are normal?
16 or 11
on a J-1939-15/CAN2.0 (on highway/off road) what is the normal speed of the data link?
250 kb/s
If a system has a twisted pair (unshielded) what is the communication speed most likely to be?
less than 10 kb/s
A tachometer circuit sometimes connects to what other circuit?
Hour meter circuit
Baud rate can be defined as?
Speed of the data transfer over the network (kb/s)
What do twisted pairs of wires that are shielded prevent?
Electromagnetic interference EMI
Fibre optic cables can communicate at what speeds?
1 Mb/s to 10 Mb/s
What is the maximum length of a stub?
one metre
A branch is a segment of data link that branches off the back bone and connects to each ________?
Node
An ECM can also be considered a ______________ on the data link?
Node
What connects all the multiplexed components of a vehicle system?
Data bus
A slower, less reliable network is usually because there is no ________________?
Protocol
What are the two common protocols in heavy duty vehicles?
J1587 and CAN
CAN stands for?
Controller area network
CAN provides a serial communications protocol, meaning?
That all the information sent on the network is in sequence
True or False
Data links only provide the transmissions of input signals between nodes and diagnostic scan tools?
FALSE
inputs and outputs
Without topology are control modules created equal or gives priorities?
Without topology all modules are created EQUAL
Data links that have terminating resistors communicate at what baud rate?
250 Kb/s
A large diameter shunt winding has what kind of resistance?
Low resistance
A small diameter shunt winding has high resistance causing what kind of speed?
Low speed in the parallel wound DC motor
What does cruise control need to function?
ECM and operator input
How many LEDs can be burnt on a ray before the light is considered bad (failed)?
1/4 of LEDS in ray
Where in the message frame is the checksum?
Appears at the end of the message and is one Byte long
Identify the order of a SAE J1939 CAN 2.0B message frame.
Arbitration field - Control Field - Data Field - CRC Field -ACK - End of Frame
CRC stands for?
Circular reference check
ACK stands for?
Acknowledge field
Three consecutive recessive bits make up what in a J1939 message?
End of frame portion (terminates message)
Is the J1939 communicate at a faster speed or slower speed than the J1587 system?
FASTER
If a J1939 message is not terminated what phenomenon will result?
Standing Waves
Reflections can cause major problems within the communications system because?
They corrupt the signal of the messages on the data link
What ohms value do J1939 resistors have?
120 ohms
What is the DISADVANTAGE to using LED lights in colder climates than incandescent?
incandescent lamps give off heat, melting snow/ice off lamps
What is an advantage to using LEDs instead of incandescent lamps? (time)
LEDs turn on faster than incandescent
What is the purpose of the DRAIN wire on a J1939 system?
To reduce EMI, grounds to battery
Protocol is what in a multiplex system?
Language
In a system with Topology, describe priorities
Topology has all nodes as equals, priorities are sent in the message
How many pins does a J1587/1708 system need?
6 PIN
How many pins are needed on a J1939 system?
9 PIN
What is the best way to test a fuel sender unit?
Ohmeter - power off
True or False The bulkhead control module can only control one other module?
False, can control many modules
What and where are _____ and ______ installed in an alternator circuit to reduce noise and interference?
In series coil (filter choke) - noise and interference
In parallel - connected capacitor (on the power lead) - interference (voltage surges)
In a dash that has fibre optics supplying light to the gauges, what could cause ALL the gauges to be dark?
Source light is out
In a dash that has fibre optics supplying light to the gauges, what would cause one gauge to be out or dimmer than the rest?
The cladding sheath is torn
What is frequency of a speed sensor measured in?
Hertz
What is the amplitude of a speed sensor measured in?
Voltage AC
