4R70W

OPERATION
The 4R70W transmission is a electronically controlled four speed automatic transmission. The Powertrain Control Module (PCM) uses inputs from various sensors to control the operation of the 4R70W transmission. The transmission control switch disables operation in fourth gear allowing automatic operation through the first three gears. The 4R70W transmission has self-test capabilities much like those in other electronic control systems.

SUBSYSTEMS AND COMPONENTS

PCM Power Relay
The PCM power relay supplies power to the PCM and PCM system-related components. When the ignition switch is turned to "RUN" or "START", voltage is applied to the PCM power relay coil, closing the relay's contacts.

Voltage is supplied to the shift solenoids, electronic pressure control (EPC) solenoid and the Torque Converter Clutch (TCC) Solenoid, through the PCM power relay.

Throttle Position (TP) Sensor
The Throttle Position (TP) Sensor is a potentiometer. The sensor output is a DC voltage that varies with throttle angle. By monitoring the TP sensor output, and other sensors, the PCM calculates the proper transmission line pressure, shift scheduling, and torque converter clutch control.

Manual Lever Position (MLP) Sensor
The Manual Lever Position (MLP) Sensor sends a signal to the PCM. This indicates the position of the transmission manual lever. The MLP sensor is located on the outside of the transmission at the manual lever.

Barometric Pressure (BARO) Sensor
The Barometric Pressure (BARO) Sensor measures barometric pressure and provides this information as a variable frequency signal to the PCM. The PCM uses this input to adjust transmission line pressure and shift scheduling for vehicle operation at higher altitudes in mountainous areas.

Programmable Speedometer/Odometer Module (PSOM)
The PSOM receives a speed signal from the Rear Anti-Lock Brake Sensor (RABS) and, using a programmed conversion constant, converts it to the standard 8000 pulses per mile vehicle speed signal. The PCM uses this speed signal and other inputs to determine the proper transmission line pressure, shift scheduling, and converter clutch control.

Transmission Speed Sensor (TSS)
The frequency of this signal is used to calculate transmission speed, which is combined with other sensor inputs to determine proper shift scheduling, capacity, and torque converter clutch control.

Brake On/Off (BOO) Switch
The Brake On/Off (BOO) Switch is used to prevent converter clutch operation when the brake has been depressed. This input is ignored if the throttle position sensor indicates more than one third throttle position.

Transmission Control Switch (TCS) and Transmission Control Indicator Light (TCIL)
The Transmission Control Switch (TCS) is a momentary contact switch. When the switch is pressed, a signal is sent to the PCM to allow automatic shifts from first through fourth gears or first through third gears only. The PCM will then energize the transmission control indicator lamp. The transmission control indicator lamp will flash if the EPC circuit is shorted.

Engine Coolant Temperature (ECT) Sensor
The Engine Coolant Temperature (ECT) sensor is a thermistor in which resistance decreases as engine coolant temperature increases. The PCM measures the voltage drop across the engine coolant temperature sensor and uses this information to help calculate fuel delivery, spark timing, EGR control, and clutch converter operation.

Air Conditioning Clutch (ACC)
The PCM receives a signal when the air conditioning compressor clutch is "ON". With the clutch "ON", the PCM may adjust transmission EPC pressure to compensate for the change in torque supply to the transmission.

Transmission Oil Temperature (TOT) Sensor
The TOT sensor is located on the transmission body. This device is a temperature sensitive thermistor. With varying temperature the resistance value of the TOT will change. The PCM monitors the voltage across the TOT to determine the temperature of the transmission oil.

The PCM uses the TOT signal to determine if a cold start shift schedule is necessary.

The shift schedule is compensated when the transmission fluid temperature is cold. The PCM strategy will also prevent converter clutch engagement when the fluid is cold.

Intake Air Temperature (IAT) Sensor
The Intake Air Temperature Sensor (IAT) is a thermistor whose resistance decreases as intake air temperature increases. The PCM measures the voltage drop across the intake air temperature sensor and uses this information to help calculate fuel delivery, spark timing, and EGR control,

Ignition
The Profile Ignition Pickup (PIP) signal is produced by a hall effect device in the distributor. It sends RPM and Crankshaft position information to the PCM. This information is used by the PCM to determine shift scheduling and EPC.

Mass Air Flow (MAF) Sensor
The Mass Air Flow (MAF) Sensor measures the amount of air flowing into the engine and outputs a voltage to the PCM. The PCM uses this input to aid in calculating fuel delivery. For transmission strategies this sensor is used for EPC pressure control, shift, and converter clutch scheduling.

Electronic Pressure Control (EPC) Solenoid
The Electronic Pressure Control (EPC) Solenoid is a Variable Force type Solenoid (VFS). The VFS is an electro-hydraulic actuator combining a solenoid and a regulating valve. It supplies Electronic Pressure Control (EPC), which regulates transmission line pressure.

Shift Solenoids (SS1,SS2)
The shift solenoids provide gear selection of first through fourth gears by controlling the pressure to the shift valves.

Torque Converter Clutch (TCC)
The Torque Converter Clutch (TCC) Solenoid provides the torque converter clutch control by shifting the converter clutch control valve to apply or release the torque converter clutch.