358 Automatic Transmissions and Transaxles Copyright by Goodheart-Willcox Co., Inc. Never assume that a connector is good just because it looks good on the outside. Separate any suspicious connectors and make a careful visual inspection for bent or corroded pins. Also, check for pins that have been pushed out of their hold- ers. Make sure there are no signs of overheating on the con- nector. Also make ohmmeter checks for continuity. When using a diagnostic chart, such as the one in Figure 14-29, always follow procedures exactly. Carefully inspect wire splices, Figure 14-30. Also, look for wires that are rubbing on moving parts or insulation that has melted on hot exhaust system components. Either of these conditions can cause a short that affects system operation and may destroy the ECM. The wiring harness in Figure 14-31 must pass through a confined area between the body and the transmission. In this situation, even slight movement or incorrect positioning can cause a problem. Testing the ECM Some manufacturers have ECM testing procedures. Most of these procedures involve checking ECM volt- age outputs. Figure 14-32 shows an ECM being tested for proper voltage at the wiring harness. This procedure must be done very carefully to prevent ECM damage. It is usually safer to check for correct voltages at the sensors rather than at the ECM. Most ECMs can only be tested by substitution. As was discussed earlier, this should be done after careful checking has determined that the ECM is the only possible source of the problem. Some manufacturers have special testers for checking the ECM. On most vehicles, however, the scan tool can be used to test the ECM. A third method of testing a solenoid is to use an amme- ter to check for excessive current draw. Most solenoids will draw one amp or less. Always check the manufacturer’s specifications for exact current draw. Checking Electric Motors Most electric motors used on modern vehicles can be checked with the appropriate scan tool. Scan tool use was discussed earlier in this chapter. The windings of some motors can be checked with an ohmmeter. Connect the ohmmeter to the input and output connectors, or to the connector and the motor body. As a general rule: • If the resistance reading is zero or very low, the wind- ing is shorted. • If the ohmmeter reads infinite resistance, the winding is open. If winding specifications are available, check that the motor winding has the proper resistance. Specifications are usually given as a range of resistance, for instance 500 to 800 ohms. Checking Wiring When troubleshooting a wiring problem, remember that for any electrical device to operate properly there must be a complete circuit. This means that voltage must be available to the device, the device must be in operating condition, and the electrical circuit must be completed through a good ground. Always obtain the proper wiring diagram when check- ing for a wiring problem. The correct wiring diagram will lead you to the most obvious connectors and trouble spots. See Figure 14-28. Figure 14-28. To properly check the electrical system of an electronic transmission or transaxle, the technician must have access to the proper electrical schematic. (General Motors) Range A Range B Range C S T A B N R P M L C C D D E 3-2 Control solenoid TCC solenoid 1-2 Shift solenoid 2-3 Shift solenoid B B B B B B A A A A A A 1149 Red Trans. temp. sensor D4 N.O. D3 N.C. D2 N.C. LO N.O. REV N.O. Pressure control solenoid Pressure switch assembly N.C. = Normally closed switch N.O. = Normally open switch E 897- Wht 422 Blk 1222 Lt grn 1223 Yel 1224 pnk 1225 Dk bluR 1226 Orn 1227 Brn 1228 Ppl 1229 Blu 455 GraM