Computer System

1
Chapter 17
Computer System Fundamentals
2
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

3
Cybernetics
4
Computer Advantages

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

5
Computer Advantages

• On-board diagnostics
• Increased driver convenience
• Improved passenger safety
• Compensation for component wear and failure to
  keep the car driveable

6
Binary Numbering System
7
Binary Numbering System

• Binary numbers can be converted into decimal
  (base ten) numbers

8
Binary Language

• Single zero or one is called a bit
• Four bits make a nibble
• Eight bits make a byte or word

9
Digital Signal

• On-off signal like that produced by a rapidly
  flipping switch

10
Analog Signal

• Gradually changes in strength like the output
  from a dimming switch

11
Analog Signal

• Analog waveform as seen onan oscilloscope

12
Scoping a Magnetic Sensor
13
Signal Frequency

• How fast a signal changes over time
• High-frequency signal
• changes frequently, completing each cycle in a
  short time
• Low-frequency signal
• changes more slowly, completing each cycle in a
  longer period of time

14
Inputs and Outputs
15
Computer System Block Diagram
Fig 18
16
Sensors

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

17
Active Sensor

• Produces its own voltage signal internally
• Signal is fed to the computer for analysis
• Shielded wire may be used to block induced
  voltage and interference in the signal wire(s)

18
Active Sensor
19
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
  received by the computer changes

20
Passive Sensor
21
Reference Voltage

• Applied to a sensor by the computer
• Usually 5 volts on most vehicles
• Computer steps down battery voltage so that a
  smooth, constant supply of dc voltage is fed to
  passive sensors
• Sensor alters the reference voltage by changing
  is internal resistance

22
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

23
Sensor Types

• Oxygen sensors
• measure the amount of oxygen in the engines
  exhaust gases
• Manifold absolute pressure sensor (MAP)
• measures the pressure inside the engine intake
  manifold
• Barometric pressure sensor (BARO)
• measures the outside air pressure

24
Sensor Types

• Throttle position sensor (TP)
• 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

25
Sensor Types

• Camshaft position sensor (CMP)
• 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

26
Sensor Types

• Oil level sensor
• 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 for the air bag system

27
Sensor Types

• Vehicle speed sensors (VSS)
• measures the vehicles road speed
• Fuel tank pressure sensor
• measures fuel tank pressure as part of some
  evaporative emission control systems
• Battery temperature sensor
• monitors battery temperature for charging system
  functions

28
Computer Names

• Automobile manufacturers have many names for
  their computers
• Here are nine of those names
• Central processing unit (CPU)
• Electronic control unit (ECU)
• Electronic control module (ECM)
• Engine control module (ECM)

29
Computer Names (continued)

• Electronic control assembly (ECA)
• Powertrain control module (PCM)
• Vehicle control module (VCM)
• Microprocessor
• Logic module

30
Computer Locations

• Computers may be located almost anywhere on the
  vehicle

31
Computer Construction

• Integrated circuits are attached to a printed
  circuit board

32
Module Memory

• ROM (Read Only Memory)
• Contains instructions that allows the module to
  perform the tasks of managing the engine, such
  as
• Programs.
• Look-up tables on how the vehicle should perform.
• Data and formulas used to perform calculations.
• Does not need applied power to store data.

33
Module Memory

• RAM (Random Access Memory)
• Non-permanent memory.
• Information is stored temporarily.
• Can be read, changed or rewritten.

34
Module Memory

• RAM (Random Access Memory)
• When power is removed, all stored data is erased.
• Used to store information
• From sensors.
• Results of calculations.
• Data subject to constant change.

35
Module Memory

• KAM (Keep Alive Memory)
• Information can be read, written and erased from
  KAM.
• KAM is not lost when ignition key is turned off.

36
Module Memory

• KAM (Keep Alive Memory)
• Disconnecting Battery will erase KAM.
• KAM allows for adaptive strategies.
• Stores diagnostic codes.

37
Module Memory

• PROM (Programmable Read Only Memory)
• Similar to ROM in that the information is
  permanent.
• Information is not lost when power is removed.
• Data or information is specific to a particular
  application.

38
Module Memory

• PROM (Programmable Read Only Memory)
• Can be reprogrammed with new information.
• Some manufacturers have a removable chip that can
  be replaced.

39
Chapter 18
On-Board Diagnostics and Scan Tools
40
On-Board Diagnostic Systems

• Modern automotive computer systems are designed
  to detect problems and indicate where they might
  be located
• This has greatly simplified the troubleshooting
  of complex automotive systems

41
OBD I Systems

• Most early on-board diagnostic systems could only
  check a limited number of items
• Diagnostics were often unable to isolate problems
  within a circuit
• There was little standardization
• each manufacturer used different connectors,
  terminology, and trouble code identification

42
OBD II Systems

• Designed to more efficiently monitor the
  condition of hardware and software that affect
  emissions
• Diagnostics can detect part deterioration, not
  just complete failure
• (Sensor at low end of operating range)
• OBD II standardized data link connectors, trouble
  codes, terminology, and scan tool capabilities
• Over 500 engine performance related codes

43
MIL OBDII

• Malfunction indicator light
• Steady glow
• Trouble is not critical but should be repaired
• Flashing
• Critical
• Trouble code could damage catalytic converter
• Intermittent code
• Not present after 50 key cycles light goes out

44
Data Link Connector

• Multipin terminal used to link the scan tool to
  the computer
• OBD I connectors came in various shapes, sizes,
  and locations
• OBD II connector is a standardized, 16-pin
  connector located under the dash

45
Scan Tool Kit

• Read the tools operating instructions. Operating
  procedures vary

46
Scan Tool Program Cartridges

• Most manufacturers release new cartridges every
  one to two years

47
Diagnostic Connector Location

• OBD II connector located below the dash

48
Diagnostic Connector Location

• This connector is located in thecenter console

49
Malfunction Indicator Lamp (MIL)

• Continuous illumination means the trouble should
  be repaired
• Flashing MIL means the trouble could damage the
  expensive catalytic converter
• Intermittent MIL means the problem is also
  intermittent

50
Diagnostic Trouble Codes

• Digital signals produced and stored by the
  computer when an operating parameter is exceeded
• Parameters include sensor voltage range, actuator
  current flow, and actuator movement

51
Computer System Problems

• Most performance problems are not caused by the
  computer controls

52
Repairing the Problem

• Always correct the cause of the lowest number
  diagnostic trouble code first and recheck for
  codes
• fixing the cause of the lowest code may clear
  other codes
• Troubles code do not always mean that a certain
  component or sensor is bad, only that the circuit
  parameters have been exceeded

53
OBD II Diagnostic Code
54
Failure Types

• Computer system failures can be grouped into two
  general types
• Hard failure
• problem that is always present
• Soft failure
• problem only occurs when certain conditions are
  present (intermittent)
• soft failure codes will be stored in memory for
  3050 ignition or warm-up cycles

55
Failure Types

• Failure types can be further broken down into
  four categories
• General circuit failure
• circuit or component has a fixed value, no
  output, or an output that is out of
  specifications
• Low-input failure
• voltage, current, or frequency is below normal
  operating parameters

56
Failure Types

• High-input failure
• signal has more voltage, more current, or a
  higher frequency than normal
• Improper range/performance failure
• sensor or actuator is producing values slightly
  lower or higher than normal
• device is still functioning, but not as well as
  it should
• OBD II systems have this capability

57
Test Drive

• You can scan the vehicle datastream while driving
  to simulate the conditions present when the
  trouble occurs
• Some scan tools allow you to take a snapshot or
  movie to play back when you are safely stopped

58
Activating Diagnostics

• Jump terminals A to B on mostGM connectors

59
Activating Diagnostics

• On Ford connectors, jump the extrapigtail to a
  specified terminal

60
Activating Diagnostics

• Connect a test light across specified terminals
  in this connector. Watch the flashes for the
  trouble codes

61
Activating Diagnostics

• Turning the ignition on, off, on, off, and then
  on within 5 seconds will activate diagnostics on
  most Chrysler cars

62
Activating Diagnostics

• By pressing two buttons at the same time, the
  readout will display trouble codes

63
Check Engine Light

• During diagnostics, the lamp mayflash to
  indicate DTCs

64
Trouble Code Chart

• Service manual chart that shows different trouble
  code numbers and possible problems and causes

65
Erasing Trouble Codes

• There are various ways to erase trouble codes
  from the computer
• Use a scan tool
• this is the easiest way
• Disconnect the battery ground cable
• Unplug the fuse to the ECM
• both methods erase radio, seat, clock, and ECM
  adaptive strategy memories

66
Erasing Trouble Codes

• After clearing codes, reenergize on-board
  diagnostics to verify that no codes are present
• This will help to verify your repair
• DTCs will be erased from memory automatically
  after 30 to 50 key cycles or warm-up cycles