WTEC III ELECTRONIC CONTROLS TROUBLESHOOTING MANUAL BASIC KNOWLEDGE 3–2. USING THE TROUBLESHOOTING MANUAL Use this manual as an aid to troubleshooting the WTEC III Electronic Controls. Every possible problem and its solution cannot be encompassed by any manual. However, this manual does provide a starting point from which most problems can be resolved. Once a problem solution is discovered in the manual do not look further for other solutions. It is necessary to determine why a problem occurred. For example, taping a wire that has been rubbing on a frame rail will not correct the problem unless the rubbing contact is eliminated. 3–3.
SYSTEM OVERVIEW WTEC III Electronic Control functions are controlled by the ECU. The ECU reads shift selector range selection, output speed, and throttle position to determine when to command a shift. When a shift occurs, the ECU monitors turbine speed, output speed, and throttle position to control the oncoming and off-going clutches during the shift. When the ECU detects an electrical fault, it logs a diagnostic code indicating the faulty circuit and may alter the transmission operation to prevent or reduce damage. When the ECU detects a non-electrical problem while trying to make a shift, the ECU may try that shift a second or third time before setting a diagnostic code.
Once that shift has been retried, and a fault is still detected, the ECU sets a diagnostic code and holds the transmission in a fail-to-range mode of operation. 3–4. IMPORTANT INFORMATION IN THE TROUBLESHOOTING PROCESS Before beginning the troubleshooting process, read and understand the following: WTEC III wire identification presents the wire number followed by the ECU terminal source (i.e., 157-S30). If there is a letter suffix following the wire number, there is a splice between the ECU source and wire destination (i.e., 136A-S16). Shut off the engine and ignition before any harness connectors are disconnected or connected. Remember to do the following when checking for shorts and opens:
Minimize movement of wiring harnesses when looking for shorts. Shorts involve wire-to-wire or wire-to-ground contacts and moving the harnesses may eliminate the problem. Wiggle connectors, harnesses, and splices when looking for opens. This simulates vehicle movements which occur during actual operation. When disconnecting a harness connector, be sure that pulling force is applied to the connector itself and not the wires extending from the connector. Resistance checks involving the wiring between the ECU connectors and other components adds about one ohm of resistance to the component resistance shown. Copyright © 2001 General Motors Corp.