Chapter 14 Troubleshooting Electronic Control System Problems 343 Copyright by Goodheart-Willcox Co., Inc. Alternator drive belt Pulley Figure 14-6. Worn and slipping alternator drive belts are the source of many computer control system complaints. Inspect the belt for a glazed or cracked surface and for proper tension. Also check the alternator drive pulley for wear. Figure 14-5. Carefully inspect wiring connections, especially those carrying low voltage sensor signals. Note the aftermarket connector in the photograph. Corrosion and overheating often occur at connectors, causing high resistance. Wiring and Connector Problems The voltages used to operate the sensors are usually much lower than battery voltage. Therefore, any wire dam- age or corrosion at the connectors greatly affects the sensor inputs to the ECM, Figure 14-5. Note that even slight resis- tance can cause incorrect sensor inputs, leading to improper or erratic shift points. A commonly overlooked wiring problem is a corroded ground connection or disconnected ground wires. Remember that the return path for the cur- rent is as important as the input path. Resistance through a ground circuit can affect several transmission control loops at once. Therefore, when a transmission/transaxle control system seems to have several unrelated or intermittent prob- lems, look for a poor ground. Another common wiring problem is a wire that has been chafed or broken by movement. This commonly occurs where wires must pass through confined spaces or small openings in the body or other sheet metal parts. Manufacturers often place electrical connectors near or under the vehicle’s battery. The battery acid and hydrogen gas often cause corrosion inside the connector. Another common problem is a wire that is allowed to touch an exhaust system part. The insulation melts and the wire grounds against the exhaust component. Battery Voltage and Computer System Operation The voltage input to the computer control system must be at or near battery voltage (12.6 volts). Defects in the charging system or battery can pull voltage below 12 volts. Low voltage can confuse the ECM, causing com- puter control system problems. In many cases, the voltage will be only slightly below normal. Slightly low voltage will cause computer control system problems but not starting problems. Typical results of low voltage include intermittent engine and/or drive train problems, or an engine or drive train problem that cannot be isolated to a specific system or component. If any of the above situa- tions occur, check the battery and charging system before performing further troubleshooting procedures. Begin by checking the tension and condition of the alternator drive belt, Figure 14-6. Also, check the belt pulley for wear or damage. If the drive belt is tight and appears to be in good condition, check the charging rate and battery condition using an electrical system tester. The Seven-Step Troubleshooting Process The seven-step troubleshooting process was dis- cussed in Chapter 13. This process can be used to diagnose electronic transmissions and transaxles, as well as hydrau- lic models. The seven steps are as follows: Step 1. Verify the problem—Interview the driver and make a road test to determine the exact problem. Step 2. Check for obvious causes—Check for obvious faults, such as disconnected wires or misadjusted linkage. Step 3. Determine which component or system is the most probable cause of the problem—Combine your knowledge and what you have learned in the previous steps to make a preliminary diagnosis of the problem. Step 4. Perform pinpoint tests—Check all systems and com- ponents, eliminating them as possibilities. Step 5. Check for related problems—Repeat test procedures, or perform new tests, to make sure that the problem identified in step 4 is the root cause of the problem.