Electronic Transmission

PCM controls transmission and other vehicle functions. PCM monitors a number of engine/vehicle functions and uses data to control shift solenoid "A", shift solenoid "B", TCC solenoid and the force motor. PCM also regulates TCC engagement, upshift pattern, downshift pattern and line pressure (shift quality).

• 1-2 & 2-3 Shift Solenoids
  
  The shift solenoid valves are 2 identical, normally open, electronic exhaust valves that control upshifts and downshifts in all forward gear ranges. These shift solenoid valves work together in a combination of ON and OFF sequences in order to control the positions of the 1-2 and 2-3 shift valve trains. PCM monitors numerous inputs in order to determine the appropriate solenoid state combination and transmission gear for the vehicle operating conditions. PCM energizes the shift solenoids by providing a ground to the solenoid's electrical circuit. This sends a current through the coil winding of the solenoid, thereby creating a magnetic field. The magnetic field repels the plunger inside the solenoid and seats the solenoid metering ball against the fluid inlet port. This action prevents the exhaust of fluid through the solenoid and provides an increase in fluid pressure at the end of the shift valves. This fluid pressure initiates an upshift by moving the shift valves. Shift solenoid resistance should measure 19-24 ohms when measured at 68°F (20°C) and 24-31 ohms when measured at 190°F (88°C). The shift solenoid valves should energize when voltage is greater than 7.5 volts and de-energize when the voltage is less than one volt.
• Transmission Fluid Pressure Manual Valve Position Switch
  
  The automatic Transmission Fluid Pressure (TFP) switch is attached to the valve body and consists of one fluid pressure switch that monitors TCC release pressure. This switch is used as a diagnostic tool to confirm that the TCC is actually OFF when it has been commanded OFF by the PCM. The TCC release switch is a normally closed pressure switch. A normally closed switch allows current to flow from the positive contact through the switch to ground when no fluid is present. Fluid pressure moves the diaphragm to disconnect the positive and ground contacts, opening the switch and stopping current flow. This change in switch status electronically signals the PCM that the TCC is released.
• TCC Pulse Width Modulation Solenoid
  
  The TCC Pulse Width Modulation Solenoid (PWM) solenoid valve is a normally closed (hydraulically) used to control the apply and release of the converter clutch. PCM operates the solenoid with a negative duty cycle at a fixed frequency of 32 Hz in order to control the rate of TCC apply/release. The solenoid's ability to ramp the TCC apply and release pressures results in smoother TCC operation. When vehicle's operating conditions are appropriate to apply the TCC, the PCM immediately increases the duty cycle to about 22 percent. The PCM then ramps the duty cycle up to a maximum of 98 percent in order to achieve full TCC apply pressure. The rate at which the PCM increases the duty cycle controls the TCC apply. Similarly, the PCM also ramps down the TCC solenoid duty cycle in order to control TCC release. Some operating conditions prevent or enable TCC apply under various conditions. Also, if PCM receives a zero voltage signal from the TCC brake switch, signaling that the brake pedal has been depressed, the PCM immediately releases the TCC. TCC duty cycle for Electronically Controlled Capacity Clutch (ECCC) equipped vehicles is 22 percent for minimum apply pressure and 43 percent for maximum apply pressure. The TCC PWM solenoid valve will typically be 40-60 percent at full apply. Your results may vary. The TCC PWM solenoid valve resistance should measure 10-12 ohms at 68°F (20°C) and 13-15 ohms when measured at 190°F (88°C).
• Transmission Fluid Temperature Sensor
  
  The automatic Transmission Fluid Temperature (TFT) sensor is a negative temperature coefficient thermistor (temperature sensitive resistor) that provides information to the PCM regarding the transmission fluid temperature. The TFT sensor clips on to the valve body and is replaced as a separate component and not as a part of the AT wiring harness assembly. The TFT sensor monitors non-pressurized fluid in the sump in order to determine operating temperature of the transmission fluid. The internal electrical resistance of the sensor varies in relation to the operating temperature of the transmission fluid. The PCM sends a 5-volt reference signal to the TFT sensor and measures voltage drop in the electrical circuit. A lower fluid temperature creates a higher resistance in the TFT sensor, which produces a higher voltage signal. PCM uses this input in order to help determine proper line pressure, shift schedules and TCC apply. When transmission fluid temperature reaches 266°F (130°C), PCM enters Hot Mode. Temperature higher than this will modify transmission shift schedules and the TCC apply in an attempt to reduce the fluid temperature by reducing the transmission heat generation. During Hot Mode, PCM applies the TCC at all times in 3rd and 4th gears. Also, PCM performs the 2-3 and 3-4 shifts earlier in order to help reduce fluid heat generation. PCM stays in Hot Mode until fluid temperature drops less than 248°F (120°C).
• Transmission Pressure Control Solenoid
  
  The transmission Pressure Control (PC) solenoid is a precision electronic pressure regulator that controls transmission line pressure based on current flow through its coil windings. As current flow is increased, magnetic field which is produced by the coil moves the solenoid's plunger further away from the exhaust port. Opening the exhaust port decreases the output fluid pressure, which is regulated by the PC solenoid. This ultimately decreases line pressure. The PCM controls the PC solenoid valve based upon various inputs including throttle position, fluid temperature, MAP sensor and gear state. PCM controls the PC solenoid valve on a positive duty cycle at a fixed frequency of 585 Hz (cycles per second). Duty cycle is defined as the percentage of time when current flows through the solenoid coil during each cycle. A higher duty cycle provides a greater current flow through the solenoid. The high (positive) side of the PC solenoid valve electrical circuit at the PCM controls the PC solenoid valve operation. The PCM provides a ground path for the circuit, monitors average current, and continuously varies the PC solenoid valve duty cycle in order to maintain the correct average current flowing through the PC solenoid valve. The PC solenoid valve resistance should be 3-5 ohms at 68°F (20°C).