WTEC III ELECTRONIC CONTROLS TROUBLESHOOTING MANUAL GENERAL DESCRIPTION Copyright © 2001 General Motors Corp. 1–4. THROTTLE POSITION SENSOR (Figure 1–6) The Throttle Position Sensor (TPS) can be mounted to the engine, chassis, or transmission. The TPS contains a pull actuation cable and a potentiometer. One end of the cable is attached to the engine fuel lever and the other, inside a protective housing, to the TPS potentiometer. Output voltage from the TPS is directed to the ECU through the external harness. The voltage signal indicates the throttle position and, in combination with other input data, determines shift timing.
A B C THROTTLE SENSOR V00628 A B C THROTTLE SENSOR V00628 Figure 1–6. Throttle Position Sensor 1–5. SPEED SENSORS (Figure 1–7) Three speed sensors — engine speed, turbine speed, and output speed — provide information to the ECU. The engine speed signal is generated by ribs on the shell of the torque converter pump. The turbine speed signal is generated by the rotating-clutch housing spline contours. The output speed signal is generated by a toothed member attached to the output shaft (except for the MD 3070, where the toothed member is the transfer case idler gear). The speed ratios between the various speed sensors allow the ECU to determine if the transmission is in the selected range.
Speed sensor information is also used to control the timing of clutch apply pressures, resulting in the smoothest shifts possible. Hydraulic problems are detected by comparing the speed sensor information for the current range to that range’s speed sensor information stored in the ECU memory. ENGINE HD/B 500 MD/B 300/B 400 MD/B 300/B 400 MD 3070 PT OUTPUT (EXTERNAL) TURBINE TURBINE RETARDER OUTPUT OUTPUT (EXTERNAL) (EXTERNAL) (INTERNAL) (EXTERNAL) (INTERNAL) V03470 Figure 1–7. Speed Sensors