OBJECTIVES. After studying Chapter 13, the reader should be able to: Describe the problems that can occur in electrical circuits. Test electrical circuits. Explain what a diagnostic trouble code (DTC) is and how it can be used by the service technician. Retrieve DTCs.
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OBJECTIVES After studying Chapter 13, the reader should be able to: • Describe the problems that can occur in electrical circuits. • Test electrical circuits. • Explain what a diagnostic trouble code (DTC) is and how it can be used by the service technician. • Retrieve DTCs. • Perform the ASE tasks related to electronic problem diagnosis and repair.
ELECTRONIC TRANSMISSION DIAGNOSIS • Electronic shift controls require the transmission technician to learn additional diagnostic and test procedures. • When diagnosing an electronic transmission, it must be determined if the cause is faulty electronic controls, a hydraulic system problem, or a mechanical system malfunction.
FIGURE 13-1 A diagnostic procedure for an electronically controlled transmission. ELECTRONIC TRANSMISSION DIAGNOSIS
ELECTRICAL CIRCUIT PROBLEMS • There are three common types of electrical problems: • Open Circuits • High-resistance Circuits • Low-resistance (short or ground).
FIGURE 13-2 An open circuit is a break in the circuit that will stop the current flow (a). Corroded or loose connections will cause high resistance that will reduce the current flow (b). (Courtesy of Chrysler Corporation) ELECTRICAL CIRCUIT PROBLEMS
FIGURE 13-3 A short circuit is a wire-to-wire connection that can reduce magnetic coil strength or allow current to flow to the wrong circuit (a) or a short to ground. (b is courtesy of Chrysler Corporation) ELECTRICAL CIRCUIT PROBLEMS
FIGURE 13-4 A ground or short-to-ground circuit occurs when damage to the insulation allows an electrical path to the metal of the vehicle (a). It can occur at a wire or inside a component (b). (Courtesy of Chrysler Corporation) ELECTRICAL CIRCUIT PROBLEMS
MEASURING ELECTRICAL COMPONENTS • In the past, technicians used a test light, jumper wire, and analog volt-ohmmeter or multimeter (a combination ammeter, ohmmeter, and voltmeter) for troubleshooting automotive electrical problems. • Today, the weathertight connectors make the use of a jumper wire very difficult
FIGURE 13-5 A fused jumper wire can be used to bypass portions of a circuit to determine where the problem is located (a). If the lights come on with the jumper wire installed, the problem is the fuse, switch, or wires to the battery (b). MEASURING ELECTRICAL COMPONENTS
FIGURE 13-6 A self-powered test light includes a battery and can be used to check for continuity (a). A nonpowered test light (b) can be used to determine if a point in a circuit has voltage (c). MEASURING ELECTRICAL COMPONENTS
FIGURE 13-6 (CONTINUED) A self-powered test light includes a battery and can be used to check for continuity (a). A nonpowered test light (b) can be used to determine if a point in a circuit has voltage (c). MEASURING ELECTRICAL COMPONENTS
FIGURE 13-7 Analog (a) and digital (b) multimeters. Do not use analog meters when testing electronic circuits unless instructed to do so. The bar graph and digital display are shown in (c ). MEASURING ELECTRICAL COMPONENTS
FIGURE 13-7 (CONTINUED) Analog (a) and digital (b) multimeters. Do not use analog meters when testing electronic circuits unless instructed to do so. The bar graph and digital display are shown in (c ). MEASURING ELECTRICAL COMPONENTS
FIGURE 13-8 Many electrical components, like this TPS, use weathertight connectors with latches to keep contacts clean and tight. MEASURING ELECTRICAL COMPONENTS
FIGURE 13-9 The positive (+) voltmeter lead is connected to the positive (+) solenoid terminal, and the negative (-) lead is connected to ground. With ground-controlled solenoids, the negative (-) lead is connected to the solenoid TCM terminal. MEASURING ELECTRICAL COMPONENTS • Measuring Voltage • A voltmeter is used to measure circuit voltage and voltage drop. • Voltage is measured by connecting the negative (-) lead to ground and probing various points along the circuit with the positive (+) lead
FIGURE 13-10 Voltage is measured by connecting one voltmeter lead (normally the negative) to ground, and probing the wire connections with the other lead. (Courtesy of Chrysler Corporation) MEASURING ELECTRICAL COMPONENTS
FIGURE 13-11 This meter is connected to measure the voltage drop across the resistor. (Courtesy of Fluke Corporation; reproduced with permission) MEASURING ELECTRICAL COMPONENTS
FIGURE 13-12 This modernized version of Ohm’s law memory triangle shows the relationship between volts, current (amps), and resistance. TECH TIP • Ohm’s law includes a formula that shows the relationship of the three important electrical values.
FIGURE 13-13 A digital multimeter being used to measure resistance. Be sure to turn off or disconnect the electrical power to the circuit when using ohmmeter functions. (Courtesy of Fluke Corporation; reproduced with permission) MEASURING ELECTRICAL COMPONENTS • Measuring Resistance • Measuring Amperage • Measuring Duty Cycle
FIGURE 13-14 A digital multimeter is being used to measure current flow. (Courtesy of Fluke Corporation; reproduced with permission) MEASURING ELECTRICAL COMPONENTS
FIGURE 13-15 Inductive ammeters can be clipped over a wire to measure the current flow without disturbing the wire connections. MEASURING ELECTRICAL COMPONENTS
FIGURE 13-16 The jaws of the amp probe are around the wire, and the probe is connected to the DMM. The circuit is drawing 2.85 amps, which is read on the volts scale of the DMM. MEASURING ELECTRICAL COMPONENTS
FIGURE 13-17 This graph shows the current flow to a solenoid. The dip near the center shows that the solenoid plunger has actually moved. TECH TIP
FIGURE 13-18 A blown fuse has been modified by soldering a short wire to each test point (a). Replacing a circuit fuse with a modified fuse provides an easy location to check the circuit’s current flow (b). This handy ammeter, called a Fuse Buddy, can be easily inserted into the fuse box (c). Note the system fuse has been inserted into the tool to protect the circuit. TECH TIP
FIGURE 13-19 Measuring solenoid duty cycle is similar to a solenoid voltage check. Note that feed-controlled circuits should be read at + duty cycle while ground-controlled circuits use a – duty cycle. MEASURING ELECTRICAL COMPONENTS
FIGURE 13-20 Two generic scan tools designed to work with most vehicles. The Mastertech (a) uses adapters to connect to the diagnostic connector and an application cartridge to provide data for a particular vehicle. The Genisys scan tool (b) has software cartridges for many vehicles. Note that the screen of (b) is showing the engine, transmission input, and transmission output rpm; transmission operating data can also be shown (c). (a is courtesy of Vetronix; b and c are courtesy of OTC) MEASURING ELECTRICAL COMPONENTS • Scan Tools • Special tools to scan data from the vehicle computers have been developed by most vehicle manufacturers.
FIGURE 13-21 This DLC (diagnostic link connector) is under the instrument panel (a). Connecting a scan tool to the DLC allows it to display and operate vehicle functions (b). MEASURING ELECTRICAL COMPONENTS
FIGURE 13-22 The first letter of an OBD-II code identifies the function of the fault code area; transmission faults will begin with P. The first digit indicates if the DTC is generic or manufacturer specific. The second digit indicates the power train system; a 7 or 8 would indicate a transmission fault. The last two digits indicate the fault. MEASURING ELECTRICAL COMPONENTS
FIGURE 13-23 The scope is displaying a secondary ignition pattern in which most spark plugs are firing at about 10 kV; one is at 25 kV (a). A digitalstyle speed sensor pattern is shown in b; note the gap indicating a possible problem in the center of the pattern. (Courtesy of Fluke Corporation; reproduced with permission) MEASURING ELECTRICAL COMPONENTS • Oscilloscopes • Interpreting Measurements
FIGURE 13-24 This transmission wire diagram shows the wire colors and terminal numbers and how the wires are connected. MEASURING ELECTRICAL COMPONENTS
FIGURE 13-25 The No. 2 VSS and park/neutral position switch on this transaxle can be replaced rather easily. ELECTRICAL/ELECTRONIC SYSTEM REPAIR • A faulty electrical component such as a switch, relay, blower motor, or clutch is usually repaired by removing and replacing (R&R) it with a new unit. • To splice a wire, you should:
FIGURE 13-26 A terminal is usually pushed into a connector until it locks into place (a). A pick tool is used to unlock the terminal for removal (b). ELECTRICAL/ELECTRONIC SYSTEM REPAIR
FIGURE 13-27 A wire stripping/crimping tool has an area designed to crimp wire terminals. A cutting area is used to cut insulation and pull it off the wire. ELECTRICAL/ELECTRONIC SYSTEM REPAIR
FIGURE 13-28 A splice can be made quickly by crimping a wire connector to the two wires. ELECTRICAL/ELECTRONIC SYSTEM REPAIR
FIGURE 13-29 A wire splice can be made by sliding the bared ends of the wires together, and then twisting them to hold them together. This connection should be soldered for security. (Courtesy of DaimlerChrysler Corporation) ELECTRICAL/ELECTRONIC SYSTEM REPAIR
FIGURE 13-30 A wire connection is soldered together using rosincore solder. ELECTRICAL/ELECTRONIC SYSTEM REPAIR
FIGURE 13-31 (a) A repaired wire connection should be insulated by wrapping it tightly with tape or using shrink tubing (b). The tubing will shrink tightly in place when heated using a hot air gun. TECH TIP
FIGURE 13-32 A signal monitor has three LEDs and wire connections for the transmission harness. On a road test, the LEDs show the electrical signals, and these should occur in the proper order. (Courtesy of J. S.Popper Inc., www.jspopper.com) ELECTRICAL/ELECTRONIC SYSTEM REPAIR
ELECTRICAL/ELECTRONIC SYSTEM REPAIR • Recalibration • A speedometer that is reading incorrectly can be recalibrated in some vehicles. • Recalibration is often necessary when a new TCM is installed. • The process must be performed exactly as directed by the manufacturer. • Adaptive Function Relearn • Electronic Control System Cautions • Diagnostic Trouble Codes (DTCs)
FIGURE 13-33 This recalibrator device can be connected into the wire connections to the VSS. The internal setting switches can be used to increase or decrease the rpm signal to correct the speedometer readings. (Courtesy of Autotrans) TECH TIP • If it becomes necessary to correct electronic speedometer readings when there is no recalibration process built into the vehicle’s operating system, an aftermarket device is available.
FIGURE 13-34 Extreme care should be used when testing components displaying the electrostatic discharge (ESD) symbol. These components can be damaged by ESD. ELECTRICAL/ELECTRONIC SYSTEM REPAIR
FIGURE 13-35 These DTCs are vehicle-model specific. They indicate the nature of the faults for a 42LE transmission. (Courtesy of Chrysler Corporation) ELECTRICAL/ELECTRONIC SYSTEM REPAIR
FIGURE 13-36 This DRB II screen shows that no fault codes are stored in the TCM memory (a); it would display a screen similar to b if there were fault codes. (Courtesy of Chrysler Corporation) ELECTRICAL/ELECTRONIC SYSTEM REPAIR
FIGURE 13-37 A visual inspection of the transmission electrical connector ensures that the terminals are clean and in good shape as well as being completely engaged. ELECTRICAL/ELECTRONIC SYSTEM REPAIR
ELECTRICAL/ELECTRONIC SYSTEM REPAIR • Signal Monitor • Forcing Shifts Electrically • Clutch Volume Index • EMI Electronic Problems
ELECTRONIC COMPONENT AND CIRCUIT CHECKS • After the nature of the problem has been determined, the faulty circuit or components should be checked to locate the exact cause. • These are often fairly simple voltage, resistance, or current flow checks. • These checks can often be made with the components mounted in their normal position. • A breakout box or test box can be connected into the circuit to allow the technician to check voltage or resistance
FIGURE 13-38 This 100-pin breakout box can be connected to a wiring harness to provide convenient points to make electrical checks. (Courtesy of SPX/O7C) ELECTRONIC COMPONENT AND CIRCUIT CHECKS
FIGURE 13-39 The external (a) and internal (b) wiring harnesses connect to the transmission electrical components. ELECTRONIC COMPONENT AND CIRCUIT CHECKS
ELECTRONIC COMPONENT AND CIRCUIT CHECKS • TCM Power Checks • Battery • To make a battery load test, you should: • TCC Checks • Solenoid Checks • Switch Checks • Speed Sensor Checks • Throttle Position Sensor Checks • Temperature Sensor Checks