NS 4 COMMUNICATIONS After studying this chapter, the reader will be able t Breakout box (BOB) 228 Serial data 218, BUS 218 Splice pack 218 AMirseeriee recy contat necrosis ancl serial CAN 221 Standard corporate Class 2 222 ol (SCP) 223 ac 221 State of heath GMLAN 222 Souza) N 222 Terminating communications used on vehicles 2. Discuss how the networks connect to the data, link connector and to other modules. 3. Explain how to diagnose mos Keyword 222 Multiplexing 218 Network 218 Node 217, Programmable controler interface (PCI) 224 Serial communicatio faults. This chapter will help you prepare for the ASE Twisted pair 218 UART 221 UART-based pro! (UBP) 224 ElectricaVElectronic Systems (A6) certfcatio content area “A” (General Electrical/Electronic ‘System Diagnosis 216‘CONVENTIONAL WIRING BETWEEN COMPONENTS. i wy motor [2 6) Las LAT souow swirci ~ ecu ecu moToR DiscRETE SIGNALS uaer TLL PX => “ye ‘COMMUNICATION HEATER rT UNE SOLENOID swe FIGURE 16-1 Module communications makes controling multiple electrical devices and accessories easier by ulizing simple low-current switches * RST eS Oe eS NEED FOR NETWORK Since the 1990s, vehicles have sed modules to control the operation of most electrical ‘components. & typical vehicle will have 10 or more modules. and they communicate with each other over data lines or hard wiring, depending on the application. ADVANTAGES Most modules are connected together in a network because of the following advantages. = A decreased number of wires are needed, thereby saving Woight and cost, as well as helping with instalation at the factory and decreased complexity, making servicing easier. = Common sensor data can be shared with those modules that may need the information, such as vehicle speed, outside air temperature, and engine coolant temperature. © SEE FIGURE 16-1 signal another module, which does the actual switching of the current to the device. a Le eS MODULES AND NODES Each module, also called a node, ‘must communicate to other modules. For example, i the driver depresses the window-down switch, the power window switch sends a window-down message to the body control module, ‘The body control module then sends the request tothe driver's side window module, This module is responsible for actually performing the task by supplying power and ground to the window lift motor in the current polarity to cause the window to {go down. The module also contains a circuit that monitors the current flow through the motor and will stop and/or reverse the window motor if an obstruction causes the window motor to {draw more than the normal amount of current. TYPES OF COMMUNICATION The types of communica tions include the following: * Differential, Inthe differential form of BUS communica tion, a diference in voltage is applied to two wires, which ‘CAN AND NETWORK COMMUNICATIONS 217PROGRAMMED TO USE VEHICLE SPEED SIGNAL POWERTRAIN CONTROL MODULE (PCM) CRUISE CONTROL MODULE DRIVER'S DOOR, MODULE (ODM) ANTILOCK BRAKE CONTROL MODULE PROGRAMMED TO USE VEHICLE SPEED SIGNAL. FIGURE 16-2 A network allows all modules to communicate with other modules are twisted to help reduce electromagnetic interference (EMD, These transfer wires are called a twisted pair. Parallel. | parallel type of BUS communication, the ‘send and receive signals are on different wires. * Serial data, The serial datas data transmitted by a series of rapidly changing voltage signals pulsed from low to high or from high to low. = Multiplexing. The process of multiplexing involves the sending of multiple signals of information at the same time over a signal wire and then separating the signals at the receiving end, ‘This system of intercommunication of computers or pr0- ccessors is referred to as a network, @ SEE FIGURE 16-2, By connecting the computers together on a communica tions network, they can easily share information back and forth, This muttiplexing has the following advantages. = Elimination of redundant sensors and dedicated wiring for these multiple sensors = Reduction of the number of wires, connectors, and circuits ‘Addition of more features and option content to new vehicles Weight reduction due to fewer components, wires, and ‘connectors, thereby increasing fuel economy Changeable features with software upgrades versus ‘component replacement 218 chapter 16 MODULE COMMUNICATIONS CONFIGURATION The three most common types of networks used on vehicles: include the following: 1. Ring link networks. In a ring-type network, all modules are connected to each other by a serial data line (in a line) Unt all are connected in a ring, @ SEE FIGURE 16-3. 2. Star link networks. In a star link network, a serial data line attaches to each module and then each is connected to a central point. This central point is called a splice ack, abbreviated SP such as in “SP 306." The splice pack uses a bar to splice all of the serial lines together. ‘Some GM vehicles use two or more splice packs to tie the modules together, When more than one splice pack Is used, a serial data line connects one splice pack to the others. In most applications, the BUS bar used in teach splice pack can be removed. When the BUS bar is removed, a special tool (42236) can be installed in place Of the removed BUS bar. Using this tol, the serial data line for each module can be isolated and tested for a pos- sible problem. Using the special tool at the splice pack ‘makes diagnosing this type of network easier than many others. @ SEE FIGURE 16-4. 8. Ring/star hybrid. In a ring/star network, the modules are connected using both types of network configura- tions. Check service information (SI) for details on how this network is connected on the vehicle being diag- nosed and always follow the recommended diagnostic steps. FREQUENTLY ASKED QUESTION What Is a BUS? A.BUS is a torm used to describe a communications 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.FIGURE 16-8 A ring link network reduces the number of wires it takes to interconnect all of the modules. Lass ¢ FIGURE 16-4 Ina star link network, al of the modules are connected using splice packs. CAN AND NETWORK COMMUNICATIONS 219.OGEEEEEa yO Ghekstar Paiste) nena woouLe Lerrenonr Doon woouLe | INSTRUMENT PANEL a HVAC. CELL PHONE MODULE MEMORY SEAT MODULE TOR ABS CONTROL MODULE FIGURE 16-5 A typical BUS system showing module CAN communications and twisted pairs of wire. 220 charter 16FREQUENTLY ASKED QUESTION What Is a Protocol? A protocolis a set of rules ora standard used between ‘computers or electronic control modules. Protocols Include the type of electrical connectors, voltage levels, and frequency ofthe transmitted messages. Protocols, therefore, include both the hardware and software needed to communicate between modules, NETWORK Pea ES PSS VES The Society of Automotive Engineers (SAE) standards Include the following three categories of in-vehicle network communications, GLASS A. Low-speed networks, meaning less than 10,000 bits per second (bps, or 10 Kbs), are generally used for trip computers, entertainment, and other convenience features. CLASS B Medium-speed networks, meaning 10,000 to 125,000 bps (10 to 125 Kbs), are generally used for information transfer among modules, such as instrument clusters, temperature sensor data, and other general uses. GLASS C High-speed networks, meaning 125,000 to 41,000,000 bps, are generally used for real-time powertrain and vehicle dynamic control. High-speed BUS communication systems now use a controller area network (CAN). @ SEE FIGURE 16-5. \ ‘BIN 16 UART-PINS FIGURE 16-6 UART serial data master control module is ‘connected to the data lik connector (DLC) at pin 9 TS CO tS POU Ce a BS) UART General Motors and others use UART communications {for some electronic modules or systems. UART is a serial data communications protocol that stands for universal asynchronous receive and transmit. UART uses a master control module connected to one or more remote modules. ‘The master control module is used to control message traffic ‘on the data line by poling all of the other UART modules. The remote modules send a response message back to the master module. UART uses a fixed pulse-width switching between 0 and 5 volts. The UART data BUS operates at a baud rate of 8,192 bps. @ SEE FIGURE 16-6. ENTERTAINMENT AND COMFORT COMMUNICATION ‘The GM entertainment and comfort (E & C) sorial data is similar to UART, but uses a 0 to 12 volts toggle. Like UART, the E & C serial data uses a master control module connected to ‘other remote modules, which could include the following: = Compact disc (CD) player ® Instrument panel (P) electrical center = Audio system (radio) CAN AND NETWORK COMMUNICATIONS 227av PIN 16 Eac-pIntis FIGURE 16-7 The E & C serial datas connected to the data link connector at pin 14 = Heating, ventilation, and air-conditioning (HVAC) pro- ‘grammer and control head = Steering wheel controls © SEE FIGURE 16-7, CLASS 2 COMMUNICATIONS class 2 is a serial ‘communications system that operates by toggling between 0 and 7 volts at a transfer rate of 10.4 Ks. Class 2 is used {or most high-speed communications between the powertrain control module and other control modules, plus to the scan tool. Class 2 is the primary high-speed serial communications system used by GMCAN (CAN), @ SEE FIGURE 16-8, KEYWORD COMMUNICATION Keyword 81, 82, and 2000 serial data are also used for some module-to-module ‘communication on GM vehicles. Keyword data BUS signals are toggled ‘rom 0 to 12 volts when communicating. The voltage ‘or the datastream is 0 volt when not communicating, Keyword ‘serial communication is used by the seat heater module and ‘others, but is not connected to the data link connector (DLC), (© SEE FIGURE 16-9. GMLAN General Motors, like all vehicle manufacturers, must use high-speed serial data to communicate with scan tools on all vehicles effective with the 2008 model year. As mentioned, the standard is called controller area network 222 cHaPter 16 CLASS 2-PIN2 ov 1 00 4 128s FIGURE 16-8 Class 2 serial data communication is accessible at the data link connector at pin 2 KEYWORD 81, 82, AND 2000 PuLeD 4 4 toao44 HIGHTO av TALK FIXED PULSE ov woth oo 0 0 on FIGURE 16-9 Keyword 82 operates at a rate of 8,192 bps, similar to UART, and keyword 2000 operates at a baud rate of 10,400 bps (the same as a Class 2 communicator (CAN), which General Motors calls GMLAN, which stands for GM local area network. General Motors uses two versions of GMLAN. = Low-speed GMLAN. The low-speed version is used for drver-controlled functions such as power windows ‘and door locks. The baud rate for low-speed GMLAN | 39,800 bps. The GMLAN low-speed serial data is not connected directly to the data ink connector and uses fone wire. The voltage toggles between 0 and 5 volts after an initial 12 volts spike, which indicates to the modules to turn on or wake up and listen for data on the line. Low-speed GMLAN is also known as single-wire CAN, or SWCAN, ands located at pin 1 of the DLC. = High-speed GMLAN. The baud rate is almost real tme at {500 Kbs. This sorial data method uses a two-twisted-wire circuit which is connected to the data link connector on pins 6 and 14. @ SEE FIGURE 16-10.FIGURE 16-10 GMLAN uses pins at terminals 6 and 14 Pin 1 is used for low-speed GMLAN on 2006 and newor GM vehicles. TWISTED PAIR (ONE TWIST PERINCH) HiGH-VOLTAGE MAGNETIC FIELD FIGURE 16-11 A twisted pairis used by several different network communications protocols to reduce interference that can be induced in the wiring from nearby electromagnetic BEM cncauentiy askep question Why Is a Twisted Pair Used? A twisted pair is where two wires are twisted to prevent electromagnetic radiation from affecting the signals passing through the wires. By twisting the ‘two wires about once every inch (9 to 16 times per oot), the interference is canceled by the adjacent wire. @ SEE FIGURE 16-11 A CANDi (CAN diagnostic interface) module Is required to bbe used with the Tech 2 to be able to connect a GM vehicle equipped with GMLAN, @ SEE FIGURE 16-12. FIGURE 16-12 A CANDi module will flash the green LED rapidly if communication is detected, DATA LINK CONNECTOR| FIGURE 16-13 A Ford OBD-| diagnostic ink connector showing that SCP communication uses terminals in cavities 1 (upper left) and 3 (lower eft ba ATL Pe te ate a BS) STANDARD CORPORATE PROTOCOL only a tow Fords had scan tool data accessible through the OBD-I data link connector. To identity an OBD-I (1988-1995) on a Ford vehicle that is equipped with standard corporate protocol (SCP) and be able to communicate through a scan tool, look for terminals in cavities 1 and 3 of the DLC. @ SEE FIGURE 16-13, CAN AND NETWORK COMMUNICATIONS 223.o \gamn/ o) FIGURE 16-14 A scan tool can be used to check commu- nications with the SCP BUS through terminals 2 and 10 and to the other modules connected to terminal 7 of the data link ‘connector. ‘ABS CONTROL DRIVER SEAT ppiven s MODULE 4 use| POWERTRAIN ‘CONTROL MODULE 4 INSTRUMENT CLUSTER FIGURE 16-15 Many Fords use UBP module communica~ tions along with CAN. ‘SCP uses the J-1850 protocol and is active with the key ‘on, The SOP signals from 4 volts negative to 4.3 volts positive, ‘and a scan tool does not have to be connected for the signal to bbe detected on the terminals. OBD-I (EECV) Ford vehicles use terminals 2 (positive) and 10 (negative) of the 16 pin data link ‘connector for network communication, using the SCP module ‘communications. UART-BASED PROTOCOL Newer Fords use the CAN for scan tool diagnosis, but stil retain SCP and UART-based protocol (UBP) for some modules. @ SEE FIGURES 16-14 AND 16-15. 224 chapter 16 FREQUENTLY ASKED QUESTION What Are U Codes? ‘The U diagnostic trouble codes were at frst “und fined” but are now network-related codes. Use the network codes to help pinpoint the circuit or module that is not working correctly. CHARS) Pee a ES ES CCD Since the late 1980s, the Chrysler Colision Detection (CCD) multiplex network is used for scan tool and module ‘communications, tis a citferentialtype communication and uses a twisted pair of wires. The modules connected to the network apply a bias voltage on each wire. CCD signals are divided into plus and minus (CCD+ and CCD-) and the voltage difference does not exceed 0.02 vol. The baud rate is 7,812.5 bps. NOTE: The “collision” in the Chrysler Collision detection BUS communications refers to the program that avoids contllets of Information exchange within the BUS, and does not refer to airbags or other accident-related clreuits of the vehie The circuit is active without a scan tool command, @ SEE FIGURE 16-16. The modules on the CCD BUS apply a bias voltage on ‘each wite by using termination resistors. @ SEE FIGURE 16-17. ‘The difference in voltage between CCD} and CCD- is less than 20 millvots. For example, using a digital meter withthe black. ‘meter lead attached to ground and the red meter lead attached atthe data link connector, a normal reading could include: = Terminal 3 = 2.45 volts = Terminal 11. = 2.47 volts ‘This is an acceptable reading because the readings are 20 millivolts 0.020 vol) of each other, If both had been exactly 2.5 volts, then this could indicate that the two data lines are shorted together. The module providing the bias votage is usu- ally the body control module on passenger cars and the front control module on Jeeps and trucks. PROGRAMMABLE CONTROLLER INTERFACE The Chrysler programmable controller interface (PCI) is a one- Wire communication protocol that connects at the OBD-II DLCInsTRUMENT CCD () CLUSTER cep) JOINT CONN. 3 FIGURE 16-16 CCD signals are labeled plus (+) and minus (-) and use a twisted pair of wires. Notice that terminals $ and 11 of the data link connector are used to access the CCD BUS from a scan tool, Pin 16 is used to supply 12 valts to the scan tool. sy Ko av BUS (+) 2siv Bus (-) 13Ko, FIGURE 16-17 The differential voltage for the CCD BUS is Created by using resistors in a module. at terminal 2, The PCI BUS is connected to all modules on the BUS ina star configuration and operates ata baud rate of 10,200, bps. The voltage signal toggles between 7.5 and 0 volt. If this, voltage Is checked at terminal 2 of the OBD-II DLC, a voltage of about 1 volt indicates the average voltage and means that the BUS is functioning and is not shorted-to-ground. PCI and CCD. are often used in the same vehicle. @ SEE FIGURE 16-18. SERIAL COMMUNICATIONS INTERFACE chrysler Used serial communications interface (SCi) for most scan tool and flash reprogramming functions until it was replaced ANTILOCK BRAKES VEHICLE THEFT DATA LINK CONNECTOR ‘ATG MODULE POWERTRAIN CONTROL MODULE FIGURE 16-18 Many Chrysler vehicles use both SCI and CCD for module communication with CAN, SCI is connected at the OBD-I data link connector (DLO) at terminals 6 (SCI receive) and 2 (SCI transmit). A scan tool must be connected to test the circuit CAN AND NETWORK COMMUNICATIONS 225,VOLTAGE 3sv FIGURE 16-19 CAN uses a differential 2sv type of module communication where the voltage on one wire is the equal but opposite voltage on the other wire, PP 1 tev When no communication is occurring, both wires have 2.5 volts applied. When ‘communication is occurring, CAN H goes up 1 10 2.5 volts and CAN L goes down 10 1.5 volts. Pt Rae ih 4 BACKGROUND Robert Bosch Corporation developed the CAN protocol, which was called CAN 1.2, in 1983. The ‘CAN protocol was approved by the Environmental Protection ‘Agency (EPA) for 2003 and newer vehicle diagnosties, and became a legal requirement forall vehicles by 2008, The CAN diagnostic systems use pins 6 and 14 in the standard 16 pin ‘OBD-I| J-1962) connector. Before CAN, the scan tool protocol had been manufacturer specific, CAN FEATURES features. ‘The CAN protocol offers the following ' Faster than other BUS communication protocols = Cost effective because itis an easier system than others touse = Loss effected by electromagnetic interference (Data is transferred on two wires that are twisted together, called twisted par, to help reduce EM! interference.) = Message based rather than address based, which makes it easier to expand = No wake-up needed because itis a two-wire system = Supports up to 15 modules plus a scan tool = Uses a 120 ohm resistor at the ends of each pair to reduce electrical noise = Applies 2.5 volts on both wires: H (high) goes to 8.5 volts when active (low) goes to 1.5 volts when active (© SEE FIGURE 16-19. 226 chapter 16 INACTIVE (RECESSIVE) ACTIVE (oman Te CAN GLASS A,B, AND G There are three classes of CAN, and they operate at different speeds. The CAN A, B, and C. networks can all be linked using a gateway within the same Vehicle. The gateway is usualy one of the many modules in the vehicle, = CANA, This class operates on only one wite at slow: speeds and is therefore less expensive to build. CAN A operates a data transfer rate of 88.83 Kbs in normal mode and up to 83.83 Kbs during reprogramming mode, CAN A, ses the vehicle ground as the signal retuen circuit, = CAN. This class operates on a two-wire network and does not use the vehicle ground as the signal return circuit. CAN B uses a data transfer tate of 95.2 Kbs. Instead, CAN B (and CAN C) uses two network wires for diferential signaling. This means that the two data signal voltages. are opposite to each other and used for error detection by constantly being compared. In this case, when the signal voltage at one of the CAN data wires goes high (CANH,, the other one goes low (CAN L}, hence the name diferential signaling. Dferential signaling Is also used for redundancy, in case one of the signal wires shorts out = CAN C. This class is the highest speed CAN protocol with speeds up to 500 Kbs, Beginning with 2008 models, all vehicles sold in the United States must use CAN BUS for scan tool communications. Most vehicle manufactur- ers started using CAN in older models: and itis easy to determine if vehicle is equipped with CAN. The CAN. BUS communicates to the scan tool through terminals 6 and 14 of the DLC indicating that the vehicle is equipped with CAN. @ SEE FIGURE 16-20. The total voltage remains constant at all times and the electromagnetic field effects of the two data BUS lines cancel teach other out. The data BUS line is protected against received radiation and is vitually neutral in sending radiationCAN BUS () MmMoBILIZER INSTRUMENT CDF) CLUSTER cco G) FIGURE 16-21 A DLC from a pre-CAN Acura, It shows torminals in cavities 4, § (grounds), 7, 10, 14, and 16 (B+) HONDA/TOYOTA COMMUNICATIONS FIGURE 16-20 A typical (generic) system ‘showing how the CAN BUS is connected to vatious electrical accessories and systems in the vehicle. FIGURE 16-22 A Honda scan display showing a B and two U codes, all indicating a BUS-related problems). EUROPEAN BUS Se ES The primary BUS communication on pre-CAN-equipped vehi- cles is ISO 9141-2 using terminals 7 and 15 at the OBD-I DLC. @ SEE FIGURE 16-21 ‘A factory scan tool or an aftermarket scan tool equipped With enhanced original equipment (OE) software is needed to access many of the BUS messages. @ SEE FIGURE 16-22. UNIQUE DIAGNOSTIC CONNECTOR Many different types of module communications protocols are used on European vehicles such as Mercedes and BMW. Most of these communication BUS messages cannot be accessed through the data link connector. To check the ‘operation of the individual modules, a scan tool equipped with CAN AND NETWORK COMMUNICATIONS 2271 rego ¥ S nan FIGURE 16-23 A typical 38-cavity diagnostic connector as ‘found on many BMW and Mercedes vehicles under the hood. ‘The use of a breakout box (808) connected to this connector, can help gain access to module BUS information, factory-type software will be needed to communicate with the module through the gateway module, @ SEE FIGURE 16-23, for an alternative access method to the modules. MEDIA-ORIENTED SYSTEM TRANSPORT BUS The media-oriented system transport (MOST) BUS uses fiber ‘optics for module-to-module communications in a ring or star configuration. This BUS system is currently being used for entertainment equipment data communications for videos, ‘GDs, and other media systems in the vehicle, MOTOROLA INTERCONNECT BUS Motorola intercon- nect (Ml is a single-wire serial communications protocol, using ‘one master control module and many slave modules. Typical application of the Ml BUS protocol is with power and memory mirrors, seats, windows, and headlight levelers. DISTRIBUTED SYSTEM INTERFACE BUS Distributed system interface (OS!) BUS protocol was developed by Motorola, and uses a two-wire serial BUS. This BUS protocol is currently being used for safety-related sensors and components. BOSCH-SIEMANS-TEMIC BUS The Bosch-Siemans- ‘Temic (8ST) BUS is another system thatis used or safety-related ‘components and sensors ina vehicle, such as airbags, The BST BUS is a two-wire system and operates up to 250,000 bos. 228 carrer 16 FIGURE 16-24 breakout box (B08) used to access the BUS terminals while using a scan tool to activate the modules, This breakout box is equipped with LEDs that light when circuits are active FREQUENTLY ASKED QUESTION How Do You Know What System Is Used? Use service information to determine which network. ‘communication protocol is used. However, due to the various systems on some vehicles, it may be easior 10 look at the data link connection to determine the system. All OBD-lI vehicles have terminals in the following cavities. Terminal 4: chassis ground Terminal 5: computer (s'gnal) ground Terminal 16: 12 volts positive ‘The terminals in cavities 6 and 14 mean that this vehicle is equipped with CAN as the only module ‘communication protocol available atthe DLO. To perform a test ofthe BUS, use a breakout box (808) to gain access tothe terminals while connecting to the vehicle, using a scan tool, @ SEE FIGURE 16-24 ‘ra typical OBD-II connector breakout box BYTEFLIGHT BUS The bytefight BUS is used in safety critical systems, such as airbags, and uses the time division multiple access (TDMA) protocol, which operates at 10 milion bps using a plastic optical iver (POF). FLEXRAY BUS FlexRay BUS is a version of byteflight and Is a high-speed serial communication system for in-vehicle networks. FlexRay is commonly used for steer-by-wire and brake-by-wire systems.FIGURE 16-25 This Honda scan tool allows the technician to turn on individual ights and operate individual power windows and other accessories that are connected to the BUS system, DOMESTIC DIGITAL BUS The domestic digital BUS, commonly designated D2B, is an optical BUS system connecting audio, video, computer, and telephone components ina single-ring structure with a speed of up to 5,600,000 bps, LOCAL INTERCONNECT NETWORK BUS Local inter- Connect network (LIN) is a BUS protocol used between inteligent sensors and actuators and has a BUS speed of 19,200 bps. NETWORK Pee aC Ey TES STEPS TO FINDING A FAULT When a network commu- nications fault is suspected, perform the following steps: STEP1 Check everything that does and does not work, Often accessories that do not seem to be con- nected can help identity which module or BUS circuit is at fault STEP 2 Perform module status test. Use a factory level scan tool or an atermarket scan tool equipped with enhanced software that allows OE-like functions. Check if the components or systems can be operated through the scan tool. @ SEE FIGURE 16-25. ESR 00:00:03 BCMBFCIDISSMTEC an eens FIGURE 16-26 Modules used in a General Motors vehicle can be “pinged!” using a Tech 2 scan tool TECH TIP = Ping modules. Start the Class 2 diagnosis by using @ scan tool and select diagnostic circuit check. If no diagnostic trouble codes (DTCs) are shown, ‘there could be a communication problem, Select ‘message monitor, which will display the status of all of the modules on the Class 2 BUS circuit, The ‘modules that are awake willbe shown as active and 01 can be used to ping individual mod- Ules of command all modules. The ping command should change the status from “active” to “inactive (@ SEE FIGURE 16-26. the scan t CAN AND NETWORK COMMUNICATIONS 229.FIGURE 16-27 Checking the terminating resistors using an ohmmeter at the DLC. NOTE: If an excessive parasitic draw is being diag- nosed, use a scan tool te ping the modules one way to determine if one of the modules is not geing to sleep and cause excessive battery drain, STEP 3 © Check state of health, Al modules on the Class 2 BUS circuit have at least one other module respon- sible for reporting state of health (SOH). fa module fails to send a state of health message within five seconds, the companion module will set a diagnos- tic trouble code for the module that did not respond. ‘The defective module is not capable of sending this message. Check the resistance of the termi ing resis- tors. Most high-speed BUS systems use resistors at each end, called terminating resistors. These resis- tors are used to help reduce interference into other systems in the vehicle. Usually two 120 ohm resistors, are installed at each end and are therefore connected electrically in parallel, Two 120 ohm resistors con- nected in parallel would measure 60 ohms if tested using an ohmmeter. @ SEE FIGURE 16-27. 230 cHAPTER 16 FIGURE 16-28 Use front-probe terminals to access the data link connector. Always follow the specified back-probe and front-probe procedures as found in service information, STEP 4 Check data BUS for voltages. Use a digital multi- ‘meter set to DC volts to monitor communications and check the BUS for proper operation. Some BUS con- ditions and possible causes include: * Signal is zero volt all ofthe time. Check for short- to-ground by unplugging modules one at a time to ‘check if one module is causing the problem. ‘Signal is high or 12 volts all of the time. The BUS circult could be shorted to 12 volts. Check with the customer to see if any service or body repair work was done recently. Try unplugging each module one ata time to pin down which module is causing the communications problem. * Avariable voltage usually indicates that messages ‘are being sent and received. CAN and Class 2 can be identified by looking at the data link con- rector for a terminal in cavity number 2. Class 2 is active all of the time the ignition is fore voltage variation between 0 and 7 volts can be ‘measured using a DMM sot to read DC volts. @ SEE FIGURE 16-28. i.” and thereHGH Low @ ‘CAN BUS LOOKS GOOD ‘CAN Low CAN HIGH » STEPS Use a digital storage oscilloscope to monitor the waveforms of the BUS Using a scope on the data line terminals can show if communication is being transmitted. Typical faults and their causes Include the following: + Normal operation. Normal operation shows vari- able voltage signals on the data lines. It is Impos- sible to know what information is being transmitted, but i there is activity with short sections of inac- tivity, this indicates normal data Ine transmission activity. @ SEE FIGURE 16-29. © High voltage. If there is a constant high-voltage signal without any change, this indicates that the data ine is shorted-to-vottage. * Zero or low voltage. Ifthe data line voltage is zero cf almost zero and not showing any higher vokage signals, then the data line is short-to-ground, Follow factory service information instructions to Isolate the cause of the fault. Ths step often involves disconnecting one madi at a time to see if itis the ‘cause ofa shor-to-ground or an open in the BUS circu STEPS FIGURE 16-29 (2) Data is sent in packets, so it is normal to see activity and then a flat line between messages. (b) A CAN BUS should show volages that are opposite when there is normal communications, CAN H circult should go from 2.5 volts at rest to 3.5 volts when active. The CAN L. clroult goes from 2.5 volts at rest to 1.5 volts when actve, eh case stun The Rado Cave No-Start Story {2005 Chol Coat ot sa. A ectrican chucked witha sbscgton ated in serve tnd dacoveed hl afte Gas 2 ta chet cud prove th argo stan, The soveorsvggesed ht ive shou be deco necnd oes treo ee fone of thw rg aa tc ae Trt Ge eit decreed wa th The eg uted ani. Appr the Cine Z otal aie ws dtd ogo th ao, ich tk tho tre BUS down When BUS comrnntatn ot te PEM alter tel Pu ono telat sth angie woul neta The rao waa opines the no-ta coctn summanr + Gomplit—The eg i not star, + Gaue-— ot Ine svc fipd th tecnican narow the cass toa ftin the rao tat tok the Cs datatne fo rune + ComectonThe rae oieo which eres proper maton he Ce 2 dea CAN AND NETWORK COMMUNICATIONS 231PIN NO. ASSIGNMENTS MANUFACTURER'S DISCRETION BUS + LINE, SAE J1850 | MANUFACTURER'S DISCRETION CHASSIS GROUND SIGNAL GROUND. MANUFACTURER'S DISCRETION KLINE, 150 9141 |. MANUFACTURER'S DISCRETION fofioviaraasstey) ,o- HAMUFACTURER'S pIscrETION BUS ~LINE, SAE J1850 | MANUFACTURER'S DISCRETION ‘OBD-IDLC 12. MANUFACTURER'S DISCRETION 3. MANUFACTURER'S DISCRETION 14, MANUFACTURER'S DISCRETION 38. LINE, 150 9141 16. VEHICLE BATTERY POSITIVE. (aa max) Li) s]a so] a] FIGURE 16-80 A 16 pin OBD-II DLC with terminals, identified, Sean tools use the power pin (16) and ground pin (4) for power so that a separate cigarette lighter plug is not necessary on OBD-lI vehicles. OEM aL Sey AILOBD-II vehicles use a 16 pin connector that includes: Pin 4 = chassis ground Pin S = signal ground Pin 16 = battery power (4 A max) (© SEE FIGURE 16-0, GENERAL MOTORS VEHICLES "SAE J-1850 (VPW, Class 2, 10.4 Kb} standard, which uses pins 2, 4,5, and 16, but not 10 = GM Domestic OBD-! Pins 1 and 8: CCM (comprehensive component monitor) slow baud rate, 8,192 UART (prior to 2008) Pin 1 (2006+): low-speed GMLAN. Pins 2 and 10: OEM enhanced, fast rate, 40,500 baud rato Pins 7 and 15: generic OBD-| Pins 6 and 14: GMLAN | 1S0 9141, 10,400 bau rate ASIAN, CHRYSLER, AND EUROPEAN VEHICLES = 180 9141-2 standard, which uses pins 4, §, 7, 15, and 16 "= Chrysler Domestic Group OBD-II Pins 2 and 10: COM Pins 8 and 14: OEM enhanced, 60,500 baud rate Pins 7 and 15: generic OBD-II ISO 9141, 10,400 baud rate 232 chapter 16 FREQUENTLY ASKED QUESTION Which Module Is the Gateway Module? ‘The gateway module is responsible for communicating with other modules and acts as the main communica- tions module for scan tool data, Most General Motors vehicles use the body control module (8CM) or the instrument panel control (IPC) module as the gateway. To verity which module is the gateway, check the ‘schematic and look for one that has voltage applied during ll ofthe following conditions. + Key on, engine off + Engine cranking + Engine running FORD VEHICLES = SAE J-1850 (PWM, 41 6 Kbs) standard, which uses pins 24,8, 10, and 16 = Ford Domestic OBD-I Pins 2 and 10: COM Pins 6 and 14: OEM enhanced, Class C, 40,500 baud rate Pins 7 and 18: generic OBD-I, ISO 9141, 10,400 baud rate TECH TIPLOW-sPEED GMLAN HIGH-SPEED GMLAN ART DATA? | FIGURE 16-31 This schematic of a Chevrolet Equinox shows that the vehicle uses a GMLAN BUS (DLC pins 6 and 14), plus a Class 2 (pin 2) and UART. Pin 1 connects to the low-speed GMLAN network 1. These of a network for module communications reduces the numberof wires and connections needed. 2. Module communication confgurations inclide ring lnk, ar ling and rng/tar hyd systems, 3. The SAE communication clasiiations for vehicle com- munications systems incide Clas A (ow speed), Class B (medium speed, and Gass C (nigh speed 4. Various module communications used on General Motors vehicles include UART, F&C, Clas 2, keyword commun'- cations, and GMLAN (CAN). aU SS Ey 4. Why is a communication network used? 2. Why are the two wires twisted if used for network ‘communications? Types of module communications used on Ford vehicles include SCP, UBP. and CAN. . Chrysler brand vehicles use SCI, CCD, PCI, and CAN ‘communications protocols, 1. Many European vehicles use an underhood electrical con- rector that can be used to access electrical components ‘and modules using a breakout box (BOB) or spacial tester. . Diagnosis of network communications includes checking the terminating resistor value and checking for changing voltage signals at the DLC. . Why is a gateway module used? What are U codes? CAN AND NETWORK COMMUNICATIONS 233.