Transmission Electronic Control

Transmission Electronic Control System

Electronic System Description
Transmission shift scheduling relies on the following:
^ Accelerator pedal position
^ Engine speed and acceleration
^ Vehicle speed and acceleration
^ Engine torque
^ Converter state as defined by engine speed
^ Turbine speed
^ Transmission range sensor position
^ Brake status
^ Speed control status
^ Tow/haul switch status
^ Transmission fluid temperature
^ Engine coolant temperature
^ PTO engaged signal
^ 4x4L status

The powertrain control module (PCM) and its input/output network control the following transmission operations:
^ VFS (shift feel)
^ Shift timing
^ Line pressure (engagement feel)
^ Torque converter clutch operation

The transmission control is separate from the engine control strategy in the PCM, although some of the input signals are shared. When determining the best operating strategy for transmission operation, the PCM uses input information from certain engine-related and driver demand-related sensors and switches. The following components are used to determine engine torque information for the transmission control strategies:
^ Crankshaft position (CKP) sensor
^ Camshaft position (CMP) sensor
^ Barometric pressure (BARO) sensor
^ Mass air flow (MAF) sensor
^ Manifold absolute pressure (MAP) sensor
^ Engine oil temperature (EOT) sensor
^ Air conditioning pressure (ACP) switch
^ Exhaust gas recirculation (EGR) valve
^ Injection pressure regulator (IPR)
^ Manifold air temperature (MAT) sensor

Any concerns with the engine sensors must be diagnosed and repaired before proceeding with diagnosis of the transmission components. Refer to the Computers and Control Systems for engine component diagnosis.

Using all of these input signals, the PCM can determine when the time and conditions are right for a shift, or when to apply or release the torque converter clutch. It will also determine the best line pressure needed to optimize shift feel. To accomplish this, the PCM uses output solenoids to control transmission operation.

The following provides a brief description of each of the sensors and actuators used by the PCM for transmission operation.

Remote Filter
This transmission is equipped with a remote transmission fluid filter. This filter passes 10 percent of the transmission fluid from the transmission through a small orifice into a serviceable filter element. The filtered fluid is then directed back into the rear lube circuit through the large opening in the remote manifold.

Transmission Output Shaft Speed (OSS) Sensor
The transmission output shaft speed (OSS) sensor is located on the extension housing. The OSS is a Hall-effect type sensor. The OSS reads the gear teeth on the park gear, different than the teeth used for park function. The OSS input to the PCM is used for shift scheduling, timing and torque converter clutch (TCC) operation vehicle speed. The OSS has bi-directional capability and has a digital output.

Engine Coolant Temperature (ECT) Sensor
The engine coolant temperature (ECT) sensor is a 2-wire thermistor sensor which changes resistance as temperature changes. The resistance of the sensor increases as engine temperature decreases and the voltage sent to the PCM increases. The PCM uses this information to help determine TCC operation.

Intake Air Temperature Sensor (IAT)
The intake air temperature (IAT) sensor is a thermistor in which resistance changes with temperature. The electrical resistance decreases as the temperature increases. The IAT provides air temperature information to the PCM which is used to help determine transmission line pressure and shift scheduling.

Accelerator Pedal Position (APP) Sensor
The accelerator pedal position (APP) sensor is mounted on the accelerator pedal on diesel applications. The APP detects the position of the accelerator pedal and inputs this information as a voltage to the PCM. The PCM uses APP sensor information to aid in determining line pressure, shift scheduling and TCC operation. Failure of this sensor will cause the transmission to operate at higher line pressure to avoid damage to the transmission. This higher line pressure causes harsh upshifts and harsh engagements.

Turbine Shaft Speed (TSS) Sensor and Intermediate Shaft Speed Sensor
The turbine shaft speed (TSS) and intermediate shaft speed sensors are a Hall-effect sensor requiring a 12-volt power and a ground. The other 2 terminals at the sensor are for TSS/intermediate shaft speed sensors output. The sensor detects teeth on the coast clutch input hub TSS and the adjacent overdrive ring gear intermediate shaft speed sensors. Both read 30 teeth per revolution. The TSS and intermediate shaft speed sensors are mounted externally on the transmission case toward the top of the driver's side. The TSS and intermediate shaft speed sensors input to the PCM is digital and used to determine line pressure, shift scheduling, timing and TCC operation.

Brake Pedal Position (BPP) Switch
Brake status comes from brake pedal position (BPP) switch. The BPP sensor supplies battery voltage to the PCM that the brake pedal is applied. The PCM uses this input to disengage the converter clutch, speed control, and auxiliary idle (if equipped).

Powertrain Control Module (PCM)
The operation of the transmission is controlled by the PCM. Many input sensors provide information to the PCM. The PCM then controls actuators which determine transmission operation.

Tow Haul Switch
The tow/haul switch is located on the end of the shift lever and is a momentary contact switch. The tow/haul switch provides a signal to the PCM when pressed by the driver, resulting in a change in shift and TCC scheduling. When the tow/haul switch has been pressed the indicator light that is located on either the end of the shift lever or on the instrument panel will illuminate "Tow/Haul - ON". When the switch is pressed again, tow/haul will be deactivated and the transmission control indicator lamp (TCIL) will turn off.

Transmission Control Indicator Lamp (TCIL)
The TCIL is used along with the tow/haul switch. The TCIL is located near the end of the shift lever and will illuminate the graphics "Tow/Haul ON" when the tow/haul switch has been pressed. The PCM controls the operation of the TCIL. The PCM may also flash the TCIL on/off to alert the driver that a transmission operational error has occurred when certain faults in monitored sensors, solenoids or other transmission components are detected.

4x4 Low Switch
The 4x4 low switch sends a ground signal to the instrument cluster when the vehicle is in 4x4L. The PCM then receives 4x4L status from the instrument cluster and adjusts the transmission shift schedule accordingly.

Transmission Solenoid Body Assembly
The PCM controls the transmission operation through:
^ seven variable force solenoids (VFS).
^ a transmission fluid temperature (TFT) sensor.
^ a manual valve.
^ an over-pressurization relief valve.

All of the above components are located on the solenoid body.
There is a solenoid dedicated to the function of each clutch. Line pressure and the torque converter clutch each have their own solenoid. Four solenoids are directly proportional; the pressure output is directly proportional to the applied DC amps. Three solenoids are inversely proportional; the pressure output is inversely proportional to the applied DC current.

Solenoids are keyed to prevent misassembly. The tan wire connectors connect to the solenoids. There are separate connectors for the TFT sensor and for the transmission range (TR-P) sensor. The 24-pin bulkhead connector completes the serviceable harness assembly and has serviceable O-ring seals. The 24-pin connector uses gold plated pins.

All of the solenoids except the line pressure solenoid can be serviced without removing the solenoid assembly from the transmission case. The solenoid assembly, which holds the solenoids, is aligned to the transmission case with permanent dowel pins. There is a filter-type gasket between the solenoid assembly and the transmission case.

Transmission Fluid Temperature (TFT) Sensor
The transmission fluid temperature (TFT) sensor twist-locks into the solenoid body. The TFT is a temperature-sensitive device called a thermistor. As the transmission fluid temperature rises, the TFT resistance decreases. The PCM monitors the voltage across the TFT sensor to determine transmission fluid temperature. The PCM uses the TFT signal as an input to determine cold and hot temperature shift and TCC scheduling.

Line Pressure Control Solenoid (PC-A)
The line pressure control (PC-A) solenoid is an inversely proportional 3-port device. The pressure output is, inversely proportional to the applied DC current supplied through an electronically controlled driver, which varies the current between 0 and 1 amp from the PCM. The PC-A solenoid controls the line pressure circuits.

Torque Converter Clutch (TCC) Solenoid
The torque converter clutch (TCC) solenoid is a directly proportional VFS. The pressure output of this 3-port device is proportional to the applied DC current supplied through an electronically controlled driver which varies the current between 0 and 1 amp from the PCM.

Shift Solenoid Pressure Control Solenoids (SSPC-A, SSPC-B, SSPC-C, SSPC-D, SSPC-E)
The intermediate (SSPC-C), low/reverse (SSPC-E) and overdrive (SSPC-B) clutches are each controlled by a directly proportional variable force shift (VFS) solenoid. The coast (SSPC-A) and the direct clutch (SSPC-D) are each controlled by an inversely proportional VFS. All shift pressure solenoids are electronically controlled by the PCM which varies the current from 0 to 1 amp (direct proportional) or 1 to 0 amp (indirectly proportional).

Line Pressure Relief Valve
The solenoid body assembly contains an over-pressurization relief valve that will limit the line pressure through the (PC-A) solenoid and feedback to the pump main regulator valve. The LPC relief valve controls line pressure spikes when cold. If this valve fails you may see concerns with the filter found in the solenoid body assembly.

Transmission Range (TR-P) Sensor Assembly
The transmission range (TR-P) sensor assembly is an internally mounted sensor that includes the detent spring, rooster comb and bracket located next to the solenoid body. The components of the TR-P sensor are factory adjusted to each other and the sensor must be installed as a calibrated assembly. The TR-P sensor contains electronic circuitry that provides the PCM a fixed frequency at a duty cycle for each of the various positions of the manual lever (PARK, REVERSE, NEUTRAL, DRIVE, M3, M2 and M1) to the PCM. The PCM uses the TR-P sensor signal for engine functions (start reverse lamps) and for line pressure control, shift scheduling and TCC operation.