Electrical Fundamentals - B Flashcards
What must be done with malfunctioning audible warning devices?
Replaced
When multiple warning lights uses same buzzer, how is it wired?
In parallel to lights with a isolating diode to prevent the other lights from activating.
The warning light control device may control what?
Either the lights battery voltage supply circuit or the lights ground circuit
Instrument and gauges
Also called meters, can be either direct or indirect
Direct acting gauges
Do not use sending units. The gauge is connected directly to source of what they are measuring.
Indirect acting gauges
Require sending units and can receive analog or digital signals
Analog gauge
Is a electromechanical device with needles or pointers that swing across a calibrated scale.
What are the 3 most common types of analog gauges
Balancing coil
Stepper motor
Air core
Directly proportional gauge
As resistance increases, level on gauge increases
Indirectly proportional gauge
As resistance increases, level on gauge decreases
Thermistor
A variable resistor whose resistance changes significantly with changes in temperature.
Digital ammeter
Uses a hall effect sensor and an integrated circuit amplifier (similar to amp clamp)
Pulses per mile (PPM)
=M x Ra x N. Where M is tire rev’s per mile, Ra is rear axle ratio, and N is number of teeth on tone ring.
How does a digital gauge receive its signal?
Over the vehicles data link
A Hall effect sensor sends an amperage signal to the ammeter by:
Using a integrated circuit amplifier
Baud rate
Is the speed of the data transfer over the network, commonly measured in kilobits per second (kb/s). One baud is the transfer of one digital signal, or bit per second
The Backbone
In most vehicles is a twisted pair of wires that are often shielded with a copper wire to prevent electromagnetic interference (EMI). Is also referred to as the data bus
Stub
Is a segment of data link that branches off the backbone and connects to each node. Can be up to 1 meter in length
Node
Is a computer or other device that has a unique network address. Each ECM is considered a node on the data link
Vehicle communication data bus
The communication network that connects to all of the multiplexed components of a vehicle system (J1708, J1939)
Protocol
Is a common language for data communication between control modules. J1587 and CAN are the common protocols in heavy duty vehicles.
(CAN) Controller Area Network
Is a communication protocol used in on-highway trucks. Provides a serial communications protocol, meaning that all of the information sent on the network is in sequence.
Data Links
Provide for the transmission of input and output signals between nodes and diagnostic scan tools
Multiplexing
Is the ability to send and receive digital electronic signals over a pair of wires (data link) at high speed
What are the advantages of using a data link over point to point wires? (4)
Minimizes the amount of electrical wiring the vehicle uses.
Provides an easy way to add electrically controlled components
Reductions to size and cost of wiring harness
Fewer wire and connectors means more reliability
What is the most popular type of multiplexing?
Time division multiplexing
The J1587/J1708 has what system limitations?
Number of nodes is limited to 20, communication speed is slow (9.6 kb/s), messages limited to maximum of 21 bytes (168 bits)
J1587 MID
Message identifier, is 1 byte long and indicates the source of the address of the transmitting node. Each node may be assigned a number between 1 and 255, most common are 128-255
J1587 PID
Parameter identifier, usually 1 byte long and indicates to what parameter the following data corresponds. Can be 0-255
J1587 Parameter data bytes
All PID’s must be followed by a least one data value. Can not exceed 18 bytes.
PID 0-127 - 1 data byte
PID 128-191 - 2 data byte
PID 192-255 - 1 to 18 data byte
J1587 Checksum
Follows the final byte of data. it is 1 byte long and completes the message
J1587 bus
Is an unshielded twisted pair cable, usually orange and white in colour, does not require termination resistors
What connector was standard between 1996 and 2001?
6 pin deutsch HD10-6-12P
What connector did most OEMs convert to in 2001?
9 pin deutsch HD10-9-1939P
J1939 PGN
Parameter group number, usually 8 bytes long and its purpose is to identify the message and its data
J1939 SPN
Suspect parameter number 19 bits, is used to identify and report where the failure has occurred
J1939 FMI
Failure mode identifier, 5 bits, identifies the type of failure
What is the order of the fields in the Can message frame?
Arbitration - Identifies priority and sender Control - Additional info Data - Additional info CRC- Checks for errors ACK - acknowledges receipt End - terminates message
J 1939 data bus cables
Yellow - the CAN high (+)
Green - the CAN low (-)
1939-11 is shielded or heavy
1939-15 is unshielded or lite
J1939 cable should have how many twists?
12 twists per foot
What does the j1939 cable have on the ends of each wire?
A 120 ohm resistor
Messages on the J1939 need to be terminated in order to minimize what?
Standing waves, which are when old messages are bounced into new messages corrupting the data in the new message.
What happens when the terminating resistors fail?
If 1 fails is missing, communication glitches will occur.
If both are missing, communication will fail all together.
What is the expected idle voltage on the J1587.
High - 3.2 - 3.9 VDC that is constantly changing
Low - 0.7 -2.0 VDC that is constantly changing
What is the expected idle voltage on the J1939
2.0 - 4.0 VDC for both the High and Low
What is the expected resistance when testing between CAN high/Can low and ground?
1 - 4 M ohms or OL
What is the expected resistance between the J1939 shield wire and a chassis ground?
0 Ohms
Control Logic
Is the ability to program certain features to automatically respond once certain conditions are met (EX. headlights automatically turn on when wipers are turned on)
Bulkhead control module
BHM, known as the brains of the system, also known as the input module
Chassis control module
CHM, also known as output module, works with the BHM to communicate input and output signals from the components connected to it.
