The Hydra-matic 4T60-E uses two ON/OFF shift solenoid valves with a 2-port design that provides for all forward gear ranges. These shift solenoid valves work together in a combination of ON or OFF sequences to direct fluid pressures to the various shift valves and apply components. The following table shows the solenoid state for each gear range:

The PCM controls the ground for the 1-2 Shift Solenoid (1-2 SS) valve, thereby commanding the solenoid ON or OFF according to transmission and vehicle operation. When the solenoid is OFF, filtered line pressure that is fed to the solenoid will cease. When energized (ON), the exhaust port is blocked, stopping the exhaust of line pressure through the solenoid. Pressure on the end of the 1-2 shift solenoid valve moves the valve against a spring force, sending line pressure into the 1-2 shift solenoid fluid passage to the 3-4 shift valve.

The 2-3 Shift Solenoid (2-3 SS) valve functions identically to the 1-2 Shift Solenoid valve in that the PCM controls the ground to the solenoid, commanding it ON or OFF. When the solenoid is OFF, filtered line pressure feeding the solenoid will cease. When energized (ON), the exhaust port is blocked, stopping the exhaust of line pressure and directing it into the 2-3 shift solenoid fluid passage. The 2-3 shift solenoid fluid pressure then feeds to the 4-3 manual downshift valve and the 3-2 manual downshift valve.

Most Hydra-matic 4T60-E transaxle models also use two solenoid valves to control TCC apply and release. The first solenoid valve in this system is the pressure controlling solenoid. It is a Pulse Width Modulation (PWM) solenoid valve that acts as a direct bias on the converter clutch regulator valve. This solenoid valve is normally open.

The other solenoid valve is an ON/OFF solenoid valve with a 2-port design that is identical to the two shift solenoid valves. This type of system provides for accurate control of regulated apply pressure that feeds the apply side of the torque converter clutch plate.

The PCM controls the Torque Converter Clutch Pulse Width Modulation Solenoid valve (TCC PWM Sol valve) by varying its operating duty cycle (ON/OFF time) from 0% to 100%. Until the transmission is operating in 3rd gear, the TCC PWM Sol valve is OFF. In this state, filtered PWM feed pressure flows at maximum pressure through the solenoid and into the PWM circuit.

When the TCC PWM Sol valve is energized, the valve operates at 32 Hz (cycles per second) and from 0% to 100% duty cycle depending on vehicle operation. The TCC PWM Sol valve is enabled to modulate the amount of PWM feed pressure passing through the solenoid, sending it to the converter clutch regulator valve. At 0% duty cycle, the torque converter clutch applies at minimum capacity. At 100% duty cycle the clutch applies at maximum capacity.

The Torque Converter Clutch Solenoid valve (TCC Sol valve) is an ON/OFF solenoid that functions in the same manner as the 1-2 shift solenoid valve and the 2-3 shift solenoid valve. As with the shift solenoids, the PCM provides the ground to command the TCC Sol. valve ON or OFF. The only difference in operation is that ignition voltage is supplied through the normally closed brake switch to the solenoid.

When the solenoid is OFF, and if the transmission is operating in third or fourth gear, the TCC signal fluid exhausts through the solenoid. When energized (ON), the exhaust port is blocked. This allows the TCC signal fluid pressure to move the converter clutch valve against the spring force and the line pressure at the opposite end of the valve.

The Vehicle Speed Sensor (VSS) system is a pulse generator consisting of a speed sensor assembly, located in the case, and a toothed speed sensor rotor, which is pressed onto the final drive assembly. As the vehicle drives forward, the speed sensor rotor also rotates. This rotation produces a variable voltage signal in the pickup coil that is proportional to vehicle speed.

This information is then sent to the PCM to indicate how fast the vehicle is traveling and to develop the shift pattern for the transmission. Other systems also use VSS information:

The Hydra-matic 4T60-E transmission uses two styles of temperature sensors. One sensor is screwed into the channel plate near the TCC accumulator bore. This sensor monitors the fluid temperatures in the cooler circuit.

The other style sensor is incorporated into the wiring harness and clips to the valve body spacer plate. This type of sensor monitors the transmission fluid temperatures in the side cover.

Both sensors are negative temperature coefficient thermistors that provide transmission fluid temperature information to the PCM. The PCM sends a 5-volt reference signal to the sensors and measures the voltage drop in the circuit. The internal resistance of the sensors changes as the operating temperature of the transmission fluid changes. The PCM then uses this information to determine when to engage or disengage the TCC.

The PCM inhibits TCC operation until the transmission fluid temperature reaches approximately 45°C (113°F). At this temperature the PCM allows the TCC to engage, if the throttle position, gear range and other vehicle operating conditions are appropriate.

Transmission fluid temperatures may become excessively high, above approximately 130°C (266°F). When this happens, the PCM modifies its shift pattern and its TCC schedules in order to reduce the heat generated by fluid coupling in the torque converter. These events occur during hot mode operation when the PCM commands the transmission into the lower gear ranges (3rd or 2nd gear) and applies the TCC.

If a situation occurs where a short or open is detected in the circuit, the PCM uses a default value for transmission temperature.