1. Chapter 17
Computer System
Fundamentals

2. Contents Cybernetics Computer advantages Digital electronics
Integrated circuits
Computer signals
Computer system operation
Sensors
Computers
Actuators

3. Computer
Complex electronic device that will produce programmed electrical output signals after receiving specific electrical input signals
Computers monitor and control all major systems of a modern vehicle

4. Cybernetics
Study of how electrical-mechanical devices can duplicate the action of the human body
Comparing the human body to a computer system is an easy way to explain this subject

5. Cybernetics

6. The Nervous System
Uses chemical-electrical signals to control the body
If you touch a sharp needle, nerve cells in your finger “fire” and send a signal through a strand of nerve cells in your hand, up your arm, and into your brain
Nerve cells in your finger are comparable to a sensor, or input device, in a computer system

7. The Brain
Uses billions of cells interconnected by linking cells called neurons
When the brain “thinks”, minute electrical impulses travel from neuron to neuron
Cells in the brain can be either charged (on) or not charged (off)

8. The Brain
By connecting all the brain cells, the brain can decide what to do in each situation
Computers produce logical outputs in a similar fashion

9. The Reflex Action
Specific brain cells are activated by the needle prick (pain) signal, and a reflex output is produced
The brain sends a signal to your arm to pull back
This is similar to the action of an actuator, or output device, in a car’s computer system

10. Computer Advantages
There are several reasons that computers are being used in modern vehicles
Computers can provide several advantages

11. Computer Advantages
Fewer moving parts to wear and go out of calibration
Reduced fuel consumption
Lower emissions
Increased engine power
Reduced vehicle weight

12. Computer Advantages On-board diagnostics Increased driver convenience
Improved passenger safety
Compensation for component wear

13. Digital Electronics
Field of study dealing with the ways a computer uses on-off signals to produce “artificial intelligence”

14. Binary Numbering System
Uses only two numbers, zero and one
Key to how computers operate
Zero (0) and one (1) can be arranged in different sequences to represent other numbers, letters, words, an input, an output, or a condition

15. Binary Numbering System
To use the binary system, a computer turns switches (transistors) on or off
Off represents zero
On represents one

16. Binary Numbering System

17. Binary Numbering System
Binary numbers can be converted into decimal (base ten) numbers

18. Binary Language A single zero or a one is called a bit
Four bits make a nibble
Eight bits make a byte or word

19. Gating Circuits Gate Common gate types:
electronic circuit that produces a specific output voltage for given input voltages
Common gate types:
NOT
AND
NAND OR
NOR

20. NOT Gate

21. AND Gate

22. NAND Gate

23. OR Gate

24. NOR Gate

25. Shows what the output of a gate will be with different inputs
Truth Table
Shows what the output of a gate will be with different inputs

26. “Thinking” with Gates
If an AND gate is compared to two switches wired in series, both switches must be on to activate the starter motor

27. Using Gates
Logic gates can be connected together to form super-complex circuits
Millions of gates can be interconnected to produce thousands of programmed outputs from numerous inputs
This is how a computer works, or thinks

28. Integrated Circuits
Electronic circuits that have been reduced in size and etched on the surface of tiny semiconductor chips

29. Integrated Circuit
Different semiconductor substances are deposited on a silicon chip and then etched to produce resistors, diodes, and transistors
Metal conductors on the top of the chip connect these various electronic components to form the circuit
Wire leads allow for input and output connections

30. Integrated Circuit Wire leads connect the chip to the metal pins.
The pins plug into or are soldered to other parts of the circuit.

31. Integrated Circuit A digital IC uses logic gates.
An analog IC increases output strength or alters output.

32. IC Construction
The circuit has been photographically reduced in size, etched on a silicon chip, and placed in a protective plastic case

33. Computer Signals Computer signal
voltage variation over short periods of time
specific arrangement of pulses or waves used to carry data, or information
Computer signals can be digital or analog

34. On-off signal like that is produced by a rapidly flipping switch
Digital Signal
On-off signal like that is produced by a rapidly flipping switch

35. A digital waveform as seen on an oscilloscope
Digital Signal
A digital waveform as seen on an oscilloscope

36. Gradually changes in strength like the output from a dimming switch
Analog Signal
Gradually changes in strength like the output from a dimming switch

37. An analog waveform as seen on an oscilloscope
Analog Signal
An analog waveform as seen on an oscilloscope

38. Scoping a Magnetic Sensor

39. Electrical Waveforms

40. Signal Frequency How fast a signal changes over time
High-frequency signal
short pulse width
Low-frequency signal
long pulse width

41. Measured in cycles per second (hertz)
Signal Frequency
Measured in cycles per second (hertz)

42. Voltage level present in the waveform
Signal Amplitude
Voltage level present in the waveform

43. Percentage of on-time compared to total cycle time
Duty Cycle
Percentage of on-time compared to total cycle time

44. Computer System Operation
There are three stages of computer system operation:
input
processing and storage
output

45. Inputs and Outputs

46. Computer System Block Diagram
Service manual drawing that shows how the sensors, the actuators, and the computer interact
Useful when trying to find out what types of sensors are used and what conditions are controlled

47. Computer System Block Diagram
Fig 18

48. Sensors
Most vehicle sensors, or transducers, change a physical condition into an electrical signal
Transduce:
to change from one form to another

49. Sensor Locations Sensors can be found almost anywhere on a vehicle:
on the engine
on or in the transmission or transaxle
in the exhaust system
on the wheel hubs
on and in the fuel tank
on the suspension
in the trunk

50. Some of the sensors located on the engine and transaxle
Sensor Locations
Some of the sensors located on the engine and transaxle

51. Sensor Classifications
Sensors can be classified into two general categories:
active sensors
passive sensors

52. Active Sensor Produces its own voltage signal internally
The signal is fed to the computer for analysis
Shielded wire may be used to block induced voltage and interference in the signal wire(s)

53. Active Sensor

54. Passive Sensor Variable resistance sensor
Voltage is fed to the sensor from the computer
Sensor resistance varies with changes in a condition
temperature, pressure, motion, etc.
As sensor resistance changes, the voltage signal sent back to the computer changes

55. Passive Sensor

56. Types of Sensors

57. Variable Resistor Sensor
Changes its resistance with a change in condition
temperature, pressure, etc.
Throttle position and temperature sensors are variable resistance sensors

58. Switching Sensor
Opens or closes the sensor circuit to provide an electrical signal
Used to detect almost any condition
Produces a digital signal
Transmission pressure switches are switching sensors

59. Magnetic Sensor Also called a permanent magnet (PM) generator
Uses part movement and induced current to produce a signal
Produces an analog signal
Used to monitor speed or part rotation
Vehicle speed and wheel speed sensors are often magnetic sensors

60. Hall-Effect Sensor
Uses a special semiconductor chip to sense part movement and speed
Produces a digital signal
Applications:
crankshaft position sensors
camshaft position sensors
distributor pickup devices

61. Uses a semiconductor chip that reacts to magnetic fields
Hall-Effect Sensor
Uses a semiconductor chip that reacts to magnetic fields

62. A reverse-biased photodiode conducts current when exposed to light
Optical Sensor
A reverse-biased photodiode conducts current when exposed to light

63. Optical Sensor
Uses light-emitting diodes and photo diodes to produce a digital signal
Used to sense part rotation and speed
Used in some distributors and as speed sensors mounted outside the speedometer

64. Piezoelectric Sensor Generates voltage from a physical shock or motion
An internal crystal produces a voltage signal proportional to the amount of vibration detected
Used to sense abnormal engine vibration caused by engine knock
knock sensor

65. Piezoelectric Sensor

66. Solar Sensor Converts sunlight directly into an electrical signal
Made of a semiconductor material that converts photons into direct current

67. Solar Sensor

68. Direction Sensor Detects the polarity of a moving magnet
Signals which direction a part is rotating
Used in some computer-controlled steering systems

69. Reference Voltage Applied to a passive sensor by the computer
5 volts on most vehicles
The computer steps down battery voltage so that a smooth, constant supply of dc voltage is fed to the sensor
The sensor changes its internal resistance to alter the reference voltage

70. Sensor Types Common sensors used in late-model vehicles:
Intake air temperature sensor (IAT)
measures the temperature of intake air as it enters the intake manifold
Engine coolant temperature sensor (ECT)
measures the temperature of engine coolant

71. Sensor Types Oxygen sensors Manifold absolute pressure sensor (MAP)
measure the amount of oxygen in the engine’s exhaust gases
Manifold absolute pressure sensor (MAP)
measures pressure inside the intake manifold
Barometric pressure sensor (BARO)
measures the outside air pressure

72. Sensor Types Throttle position sensor (TP) Engine speed sensor
measures the opening angle of the throttle valves to detect driver power demand
Engine speed sensor
measures engine rpm
Crankshaft position sensor (CKP)
measures crankshaft position and speed

73. Sensor Types Camshaft position sensor (CMP) Mass airflow sensor (MAF)
measures camshaft position and rotation
Mass airflow sensor (MAF)
measures the amount of intake air flowing into the engine
Knock sensor (KS)
detects engine pinging, preignition, or detonation

74. Sensor Types Transaxle/transmission sensor Brake switch
checks transaxle or transmission gear selection
Brake switch
detects brake pedal application
Wheel speed sensor
measures wheel rotational speed for anti-lock brake and traction control application

75. Sensor Types Oil level sensor EGR sensor Impact sensors
measures the amount of oil in the engine oil pan
EGR sensor
measures the position of the exhaust gas recirculation valve pintle
Impact sensors
detect a collision

76. Sensor Types Vehicle speed sensor (VSS) Fuel tank pressure sensor
measures the vehicle’s road speed
Fuel tank pressure sensor
measures fuel tank pressure as part of some evaporative emission control systems
Battery temperature sensor
monitors battery temperature so the computer can adjust charging system output as needed

77. Circuit Sensing
Involves using the computer itself to monitor component and circuit operation
Computer monitors current flow through various circuits to diagnose:
fuel injectors
ignition coil action
computer operation

78. Computers
The term computer refers to any electronic circuit configuration that can use multiple inputs to determine outputs

79. Computer Names
Automobile manufacturers have many names for their computers:
central processing unit (CPU)
electronic control unit (ECU)
electronic control module (ECM)
engine control module (ECM)
(Continued)

80. Computer Names electronic control assembly (ECA)
powertrain control module (PCM)
vehicle control module (VCM)
microprocessor
logic module

81. Computer Types Several types of computers can be used in a car
The most common types are:
Vehicle control module
coordinates engine, transmission, traction control, and anti-lock brake functions
Powertrain control module
monitors and controls the engine and transmission

82. Computer Types Engine control module Anti-lock brake module
controls engine management functions
Anti-lock brake module
controls anti-lock brake operation
Instrumentation module
operates the digital dash display

83. Computer Types Ignition module Suspension system module
controls ignition functions, such as timing
Suspension system module
controls ride stiffness or shock absorber action
Climate control module
controls the operation of the heating, ventilation, and air conditioning systems

84. Computer Types Air bag module High-power module Body module
controls the vehicle’s air bag system
High-power module
Controls current or processes output signals from a few sensors and the main computer
Body module
coordinates body functions, such as lighting, radio, driver’s information center, electronic compass, etc.

85. Computers may be located almost anywhere on the vehicle
Computer Locations
Computers may be located almost anywhere on the vehicle

86. Computer Construction
Computers are composed of printed circuit boards, integrated circuits, capacitors, resistors, transistors, and other electronic components

87. Parts of a Computer A computer can be divided into 11 basic parts:
voltage regulator
amplifiers
conditioners
buffer
microprocessor
memory
clock
output drivers
circuit board
harness connector
computer housing

88. Parts of a Computer

89. Voltage Regulator
Provides a reduced voltage for the components in the computer and sensors
Provides a smooth dc voltage that does not vary and is free of any spikes (abrupt changes in voltage)

90. Computer Amplifier
Strengthens various signals when inside the computer
amplifier might increase the voltage signal from the oxygen sensor, which is less than one volt
Allows a low voltage signal to be used by the circuits in the computer

91. Input Conditioner Also called a converter or interface
Alters the input signals from some sensors
Modifies incoming data so that it can be utilized by the computer
Converts analog signals to digital signals

92. Output Conditioner Also called a converter or interface
Changes output signals from digital to analog
Allows the operation of actuators
Protects the computer processor from high current

93. Buffer Serves as a temporary storage area for data
Protects internal components from improper data
controls the rate of data flow
Built into the input conditioner

94. Microprocessor
Integrated circuit capable of analyzing data and calculating appropriate outputs
Uses the binary number system to make decisions, comparisons, or calculations
Compares input signals to memory data to decide what the outputs should be for maximum efficiency

95. Computer Data Flow
The interaction between the different computers in a vehicle's computer network is referred to as multiplexing

96. Computer Memory
Uses gates that are capable of storing data as voltage charges
ICs inside the memory chips will hold the data until needed by the microprocessor

97. RAM Random access memory Stores information or data temporarily
Data is erased if battery power is removed

98. ROM
Read only memory
Stores permanent data that cannot be removed from memory
Contains calibration tables and lookup tables for the general vehicle make and model

99. PROM Programmable read only memory
Contains permanent data that is more specific than the data stored in ROM
engine and transaxle specifications, vehicle weight, and tire size are specifics found in the PROM
May be replaced or reprogrammed to upgrade vehicle operation

100. EPROM Erasable programmable read only memory
Can be changed, usually by the manufacturer using special equipment
Used for storing odometer readings on an electronic dash display

101. EEPROM Electrically erasable programmable read only memory
Can be altered by the technician in the field
Allows the manufacturer to change operating parameters if a performance or driveability problem is discovered

102. Other Memories Flash erasable programmable read only memory (FEPROM)
similar to EEPROMs in all respects
Keep alive memory (KAM)
memory chip that allows the computer to have an adaptive strategy
stores calibration information that enhances vehicle operation as parts wear

103. Output Drivers Control current flow through the actuators
When energized by the computer, drivers ground the actuator circuits, providing actuator operation

104. Processor-Memory Bus
Pathway by which sections of a computer communicate
Microprocessor controls this flow of data
writes data about vehicle operation into memory and reads data about how the vehicle should operate from memory

105. Multiple Sensor Inputs
Computer system uses inputs from more than one sensor to make most control decisions
Fuel injection example:
engine coolant temperature sensor signals a cold engine
computer would use both speed and temperature signals to increase injector pulse width to enrich the mixture for cold engine operation

106. Multiple Sensor Inputs

107. Computer Network
Series of computers that control different systems but work together to improve overall vehicle efficiency
Shares wires, input signals, and output signals
Computers exchange data from sensors to prevent duplication of parts and to reduce wiring

108. Actuators
Devices that allow the computer to do work and alter the operation of other components
Actuators may be found anywhere on the modern automobile

109. Actuator Classifications
Actuators can be grouped into the following categories:
solenoid
relay
servo motor
display device
control module

110. Actuator Classifications

111. Actuator Operation
When the computer turns on an actuator, it normally provides the device with a ground circuit
Current can then operate the actuator

112. Actuator Operation

113. Solenoid Operation Computer grounds the solenoid circuit
Current flows through the solenoid winding
A magnetic field moves the plunger mounted in the solenoid windings
Plunger movement is used to operate a device
fuel injectors, vacuum valves, door locks, etc.

114. Solenoid Operation (Automatic Door Locks)

115. Relay Operation Computer grounds the relay coil windings
Low current flows through the relay windings
Relay coil field will then pull the mechanical contacts closed, allowing high current to flow to the load

116. Relay Operation

117. Servo Motor Operation
Computer can ground the motor circuit, turning the motor on and off or reversing motor rotation as needed
Some servo motors are simply reversible dc motors
these motors turn a threaded mechanism to produce controlled movement of a part

118. Specific coils can be energized to attract and stop the armature
Servo Motor Operation
Specific coils can be energized to attract and stop the armature

119. Specific Actuators Common actuators used on modern vehicles include:
Fuel injector
solenoid valve that controls fuel flow
Fuel pump
electric motor-driven pump

120. Specific Actuators Idle air solenoid Idle speed motor EGR solenoids
controls airflow into the engine to control idle speed
Idle speed motor
reversible dc motor that opens and closes the throttle valve to control idle speed
EGR solenoids
open and close small ports to control exhaust gas flow back into the engine

121. Specific Actuators Canister purge solenoids Door lock motors
control vacuum flow to draw fuel vapors from the fuel tank into the engine for burning
Door lock motors
solenoids that move latch mechanisms to lock or unlock the doors
Electric seat motors
reversible dc motors that move the seat into the desired position

122. Specific Actuators Ignition coil Ignition module
changes low voltage into high voltage, which operates the spark plugs
Ignition module
uses computer signals to control the operation of the ignition coils