270 Automatic Transmissions and Transaxles Copyright by Goodheart-Willcox Co., Inc. Coil Plunger Solenoid housing + From ECM Return spring Ground Figure 12-2. A transducer consists of a metal plunger sur- rounded by a metal coil. Current flows through the wire when- ever the ignition is on. Movement of the plunger changes the amount of current flowing in the wire. This affects the voltage sent to the ECM. Rotating teeth create magnetic field in pickup coil of conventional electronic system, sending voltage signal to module S N S Module Figure 12-3. A—The relationship of the speed sensor and the shaft-mounted rotor. Rotation of the rotor induces a magnetic field in the sensor. This creates a voltage signal that is sent to the ECM. B—This photo shows the sensor and rotor from one automatic transmission. A B Shaft from manual valve lever Manual valve lever position sensor (MVLPS) Valve body assembly Solenoid assembly Figure 12-4. The manual valve position sensor is installed on some electronically controlled transmissions and transaxles. This illustration shows the position of the sensor in the valve body. and moves in relation to the inductors when the lever is operated. When the shift lever is moved, movement of the damping element causes changes in the magnetic fields of the inductors. Changes in the magnetic fields affect current and voltage in the inductor circuits. The ECM reads these changes as shift lever position. Other Input Sensors: Transmission In addition to the sensors discussed above, other sen- sors are used throughout the vehicle. Three of these sensors can be found inside the transmission or transaxle. Pressure Sensors Every electronically controlled transmission or trans- axle has several pressure sensors. Most pressure sensors are simple on-off switches. They are connected to pressure passages in the transmission that feed certain clutches and bands. When the clutch piston or band servo is pressurized, the pressure also operates the pressure switch. Whether the pressure switches are on (pressure at the switch port) or off (no pressure at the switch port) tells the ECM what gear is engaged. The design of these switches is similar to that of the oil pressure switches used on engines with oil pressure lights. When no oil pressure is present, the diaphragm can- not close the contacts. When pressure reaches the switch, the diaphragm is pushed up, causing the contacts to close. Figure 12-5A shows a pressure sensor that completes a cir- cuit between two electrical components. Note that it has two terminals. Figure 12-5B shows a single-terminal pressure sensor. This sensor grounds through the transmission case to complete the circuit. Note: Switches held closed by spring pressure until hydraulic pressure is present are called normally closed, or NC, switches. Switches held open until hydraulic pressure is present are called normally open, or NO, switches. Transmission Temperature Sensors Temperature has a large effect on the operation of the transmission fluid. Fluid temperature can affect the vis- cosity (thickness) of the fluid and the holding ability of the clutches and bands. Therefore, many transmissions have temperature sensors. There are two types of temperature sensors. The simplest type of temperature sensor is the on-off switch, Figure 12-6. This switch can be normally