Electronic Transmission

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

• 1-2 & 3-4 Shift Solenoid Valves
  
  The 1-2 and 2-3 shift solenoid valves (also called "A" and "B" solenoids) are identical devices that control the movement of the 1-2 and 2-3 shift valves (the 3-4 shift valve is not directly controlled by a shift solenoid). The solenoids are normally-open exhaust valves that work in four combinations to shift the transmission into different gears. The PCM energizes each solenoid by grounding the solenoid through an internal quad driver. This sends current through the coil winding in the solenoid and moves the internal plunger out of the exhaust position. When on, the solenoid redirects fluid to move a shift valve. PCM-controlled shift solenoids eliminate the need for TV and governor pressures to control shift valve operation.
• 3-2 Shift Solenoid Valve
  
  The 3-2 shift solenoid valve assembly is a normally-closed, 3-port, on/off device that is used in order to improve the 3-2 downshift. The solenoid regulates the release of the 3-4 clutch and 2-4 band apply.
• Transmission Pressure Control Solenoid
  
  The transmission pressure control solenoid is an electronic pressure regulator that controls pressure based on the current flow through its coil winding. The magnetic field produced by the coil moves the solenoid's internal valve which varies pressure to the pressure regulator valve. PCM controls the pressure control solenoid by commanding current between 0.1-1.1 amps. This changes the duty cycle of the solenoid, which can range between 5-95 percent (typically less than 60 percent). High amperage (1.1 amps) corresponds to minimum line pressure, and low amperage (0.1 amp) corresponds to maximum line pressure (if the solenoid loses power, the transmission defaults to maximum line pressure). The PCM commands the line pressure values, using inputs such as engine speed and throttle position sensor voltage. The pressure control solenoid takes the place of the throttle valve or the vacuum modulator.
• Torque Converter Clutch Solenoid Valve
  
  The TCC solenoid valve is a normally-open exhaust valve that is used to control torque converter clutch apply and release. When grounded (energized) by the PCM, the TCC solenoid valve stops converter signal oil from exhausting. This causes converter signal oil pressure to increase and move the TCC solenoid valve into the apply position.
• TCC Pulse-Width Modulation Solenoid Valve
  
  The PCM energizes the Torque Converter Clutch Pulse-Width Modulated (TCC PWM) solenoid valve, which is located on transmission valve body. The TCC PWM solenoid valve acts on the TCC apply valve in order to control the torque converter clutch application. TCC PWM solenoid valve is pulse-width modulated by PCM. This means that the PCM pulses the solenoid so that the hydraulic pressure against the torque converter clutch modulates. This modulated pressure allows the TCC to slip slightly, thus keeping the TCC balanced just at the point of engagement.
• Transmission Fluid Pressure Manual Valve Position Switch
  
  A gear range sensing device called an automatic Transmission Fluid Pressure (TFP) manual valve position switch assembly is used by the PCM in order to sense which gear range has been selected by the vehicle operator. The TFP manual valve position switch assembly is located on valve body and consists of 5 pressure switches combined into one unit. PCM applies system voltage to the TFP manual valve position switch assembly on 3 separate wires. These 3 circuits are either grounded or open, depending on which gear range has been selected, and on which combination of the 5 switches gave pressure applied to them. When vehicle is in PARK, with ignition on and engine off, the normal state of the TFP manual valve position switch assembly will be DRIVE 2. When engine is running, the normal state of the TFP manual valve position switch assembly is in PARK/NEUTRAL. There are 2 possible combinations of the switches within the pressure switch manifold that do not represent an actual gear range. If PCM detects either of these combinations, then a DTC will set.
• Transmission Fluid Temperature Sensor
  
  The automatic Transmission Fluid Temperature (TFT) sensor is part of the automatic Transmission Fluid Pressure (TFP) manual valve position switch. The TFT sensor is a resistor or thermistor, which changes value based on temperature. The sensor has a negative-temperature coefficient. This means that as the temperature increases, resistance decreases and as temperature decreases, resistance increases. PCM supplies a 5-volt reference signal to the TFT sensor and measures voltage drop in the circuit. When transmission fluid is cold, sensor resistance is high and PCM detects high signal voltage. As fluid temperature warms to a normal operating temperature, resistance becomes less and signal voltage decreases. PCM uses the TFT sensor information to control shift quality and TCC application.
• Transmission Range Switch
  
  The Transmission Range (TR) switch is part of the Park/Neutral Position (PNP) and backup light switch assembly, which is externally mounted on the transmission manual shaft. The TR switch contains four internal switches that indicate the transmission gear range selector lever position. PCM supplies ignition voltage to each switch circuit. As the gear range selector lever is moved, the state of each switch may change, causing the circuit to open or close. An open circuit or switch indicates a high voltage signal. A closed circuit or switch indicates a low voltage signal. PCM detects the selected gear range by deciphering the combination of the voltage signals. PCM compares the actual voltage combination of the switch signals to a TR switch combination chart stored in memory.