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start Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 53, the reader should be able to: • • • Prepare for ASE Electrical/Electronic Systems (A6) certification test content area “A” (General Electrical/Electronic Systems Diagnosis) Explain the purpose and function of onboard computers List the various parts of an automotive computer Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 53, the reader should be able to: • • List five input sensors List four devices controlled by the computer (output devices) Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: actuator • analog-to-digital (AD) converter binary central processing unit (CPU) • clock generator • controller • controller area network (CAN) digital • duty cycle EEPROM • E2 PROM • electronic control assembly (ECA) • electronic control module (ECM) • electronic control unit (ECU) • engine mapping Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: high-side drivers (HSD) input conditioning keep-alive memory (KAM) low-side drivers (LSD) multiplexing • network • nonvolatile output drivers Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: power train control module (PCM) • programmable readonly memory (PROM) Random-access memory (RAM) • read-only memory (ROM) serial data • splice pack terminating resistors • volatile Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 COMPUTER CONTROL Modern automotive control systems consist of a network of electronic sensors, actuators, and computer modules designed to regulate the power train and vehicle support systems. The power train control module (PCM) is the heart of this system. It coordinates engine and transmission operation, processes data, maintains communications, and makes the control decisions needed to keep the vehicle operating Automotive computers use voltage to send and receive information. It converts input or data into voltage signal combinations that represent a variety of information—temperature, speed, or even words and letters, and then delivers the data in computed or processed form Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 THE FOUR BASIC COMPUTER FUNCTIONS Operation of a computer can be divided into four basic functions: Input Processing Storage Output Figure 53–1 All computer systems perform four basic functions: input, processing, storage, and output Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Input First, the computer receives a voltage signal (input) from an input device. The device can be as simple as a button or a switch on an instrument panel, or a sensor on an automotive engine. Vehicles use mechanical, electrical, and magnetic sensors to measure factors such as speed, engine RPM, air pressure, oxygen content of exhaust gas, airflow, and engine coolant temperature. Figure 53–2 A potentiometer uses a movable contact to vary resistance and send an analog voltage to the PCM The signals must undergo input conditioning. Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Processing Input voltage signals received by a computer are processed through a series of electronic logic circuits maintained in its programmed instructions. These logic circuits change the input voltage signals, or data, into output voltage signals or commands Storage The program instructions for a computer are stored in electronic memory. Some programs may require that certain input data be stored for later reference or future processing. In others, output commands may be delayed or stored before they are transmitted to devices elsewhere in the system Computers have two types of memory: permanent and temporary. Permanent memory is called readonly memory (ROM) because the computer can only read the contents; data is retained even when power to the computer is shut off Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SAE COMMUNICATION CLASSIFICATIONS The Society of Automotive Engineers (SAE) standards include three categories of invehicle network communications, including: Class A Lowspeed networks (less than 10,000 bits per second [10 kbs]) are generally used for trip computers, entertainment, and other convenience features. Most lowspeed Class A communication functions are performed using the following: UART standard (Universal Asynchronous Receive/Transmit) used by GM (8192 bps) CCD (Chrysler Collision Detection) by Chrysler (7812.5 bps) NOTE: The “collision” in CCDtype bus communication refers to the program that avoids conflicts of information exchange within the bus, and does not refer to airbags or other accidentrelated circuits of the vehicle Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Chrysler SCI (Serial Communications Interface) is used tocommunicate between the engine controller and a scan tool (62.5 kbps) ACP (Audio Control Protocol) is used for remote control of entertainment equipment (twisted pairs) on Ford vehicles Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Class B Mediumspeed networks (10,000 to 125,000 bits per second [10 to 125 kbs]) are generally used for information transfer among modules, such as instrument clusters, temperature sensor data, and other general uses General Motors GMLAN; both lowand mediumspeed and Class 2, which uses 0to 7volt pulses with an available pulse width. Meets SAE 1850 variable pulse width (VPW) Chrysler Programmable Communication Interface (PCI). Meets SAE standard J1850 pulse width modulated (PWM) Ford Standard Corporate Protocol (SCP). Meets SAE standardJ1850 pulse width modulated (PWM) Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Class C Highspeed networks (125,000+ bits per second) are generally used for real time power train and vehicle dynamic control. Figure 53–17 A typical bus system showing module CAN communications and twisted pairs of wire Most highspeed bus communication is controller area network or CAN. Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 What is a Bus? A bus is a term used to describe a communication network Therefore, there are connections to the bus and bus communications, both of which refer to digital messages being transmitted among electronic modules or computers Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 MODULE COMMUNICATION DIAGNOSIS Most vehicle manufacturers specify a scan tool be used to diagnose modules and communications. Some tests of the communication bus (network) and some of the service procedures require a DMM, set to DC volts, to monitor communications. Variable voltage indicates messages are being sent and received Most highspeed bus systems use resistors at each end called terminating resistors to help reduce interference into other systems in the vehicle. Usually two 120ohm resistors are installed at each end and connected electrically in parallel. Two 120ohm resistors connected in parallel would measure 60 ohms if being tested using an ohmmeter See Figure 53–18 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 53–18 Checking the terminating resistors using an ohmmeter at the DLC Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBD II DATA LINK CONNECTOR All OBD II vehicles use a 16pin connector that includes: Pin 4 = chassis ground Pin 5 = signal ground Pin 16 = battery power (4A max) Figure 53–19 Sixteen-pin OBD II DLC with terminals identified Scan tools use the power pin (16) ground pin (4) for power so that a separate cigarette lighter plug is not necessary on OBD II vehicles Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Vehicles may use one of two major standards including: ISO 91412 Standard (ISO = International Standards Organization) Pins 7 and 15 (or wire at pin 7 and no pin at 2 or a wire at 7 and at 2 and/or 10) SAE J1850 Standard (SAE = Society of Automotive Engineers) Two types: VPW (variable pulse width) PWM (pulse width modulated) Pins 2 and 10 (no wire at pin 7) Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 General Motors vehicles use: SAE J1850 (VPW—Class 2—10.4 kb) standard, which uses pins 2, 4, 5, and 16 and not 10 GM Domestic OBD II Pin 1 and 9—CCM (Comprehensive Component Monitor) slow baud rate—8192 UART Pins 2 and 10—OEM Enhanced—Fast Rate—40,500 baud rate Pins 7 and 15—Generic OBD II—ISO 9141—10,400 baud rate Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Chrysler, European, and Asian vehicles use: ISO 91412 standard uses pins 4, 5, 7, 15, and 16 Chrysler OBD II Pins 2 and 10—CCM Pins 3 and 14—OEM Enhanced—60,500 baud rate Pins 7 and 15—Generic OBD II ISO 9141—10,400 baud rate Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Ford vehicles use: SAE J1850(PWM) (PWM—41.6 kb) standard, which uses pins 2, 4, 5, 10, and 16 Ford Domestic OBD II Pins 2 and 10—CCM Pins 6 and 14—OEM Enhanced—Class C—40,500 baud rate Pins 7 and 15—Generic OBD II—ISO 9141—10,400 baud rate Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY The Society of Automotive Engineers (SAE) standard J1930 specifies that the term power train control module (PCM) be used for the computer that controls the engine and transmission in a vehicle The four basic computer functions include input, processing, storage, and output Readonly memory (ROM) can be programmable (PROM), erasable (EPROM), or electrically erasable (EEPROM) Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY (cont.) Computer input sensors include engine speed (RPM), MAP, MAF, ECT, O2S, TP, and VS A computer can only turn a device on or turn a device off, but it can do the operation very rapidly Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 end Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458
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