Chapter 14 Troubleshooting Electronic Control System Problems 341 Copyright by Goodheart-Willcox Co., Inc. Figure 14-2. A manufacturer’s list of possible problems for one electronic transmission. Symptoms will vary from one manufacturer to another, as well as from one type of transmission or transaxle to another. (General Motors) metal particles are produced as part of normal operation, and they often become stuck on the sensor magnet, affect- ing the production of the magnetic field. Wheel-mounted speed sensors can be damaged by road debris, or they can become coated with road tar. Temperature sensors that are defective or produce out- of-range signals can cause hard or soft shifts. Some defec- tive temperature sensors can keep the transmission from upshifting or prevent converter clutch apply. A common cause of engine temperature sensor problems is cooling system deposits that coat the sensor element. This causes the sensor to respond slowly or not at all to temperature changes. Other sensors can indirectly affect shift speeds and shift quality. Most defects in engine sensors will show up first as engine-related problems. Defective pressure or tem- perature switches in the transmission or transaxle will usu- ally not cause engine problems. Electronic Component Malfunctions Component/system Can affect Throttle position (TP) sensor • Shift pattern (erratic) • Shift quality (firm or soft) • Engine (rough) Automatic transmission output shaft speed (AT OSS) sensor • Shift pattern (erratic) • TCC solenoid valve apply (at wrong time) • Shift quality (harsh or soft) Transmission fluid pressure (TFP) manual valve position switch • TCC solenoid valve apply (no apply if diagnostic code is set) • Shift pattern (no fourth gear in hot mode) • Shift quality (harsh) • Line pressure (high) • Manual downshift (erratic) Automatic transmission fluid temperature (TFT) sensor • TCC solenoid valve control (on or off) • Shift quality (harsh or soft) Engine coolant temperature (ECT) sensor • TCC solenoid valve control (no apply) • Shift quality (harsh) Shift solenoid valves • Gear application (wrong gear, only two gears, no shift) Brake switch • TCC apply (no apply) • No 4th gear if in hot mode System voltage • Line pressure (high) • Gear application (third gear only) • TCC control (no apply) • No 4th gear if in hot mode 3-2 control shift solenoid valve assembly • Gear application (third gear only) • 3-2 downshifts (flare or tie-up) Pressure control solenoid • Line pressure (high or low) • Shift quality (harsh or soft) TCC solenoid valve • TCC solenoid valve apply (no apply) • No 4th gear if in hot mode Cruise control • Delays 3-4 upshift and TCC apply during heavy throttle Acceleration slip regulation (ASR) • Downshifts