Transmission Electronic Control System
Transmission Electronic Control System
Electronic System Description
Transmission shift scheduling relies on the following:
- Accelerator Pedal Position (APP)
- Engine speed and acceleration
- Vehicle speed and acceleration
- Engine torque
- Converter state as defined by engine speed
- Turbine speed
- Transmission Range (TR) sensor position
- Brake status
- Speed control status
- Transmission Fluid Temperature (TFT)
- Engine Coolant Temperature (ECT)
The PCM and its input/output network control the following transmission operations:
- Variable force shift (shift feel)
- Shift timing
- Line pressure (engagement feel)
- Torque Converter Clutch (TCC) 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
- A/C pressure switch
- EGR valve
- Injection Pressure Regulator (IPR)
- Intake Air Temperature (IAT) sensor
Any concerns with the engine sensors must be diagnosed and repaired before proceeding with diagnosis of the transmission components. Refer to the engine for 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 TCC. 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.
Output Shaft Speed (OSS) Sensor
The sensor is located on the extension housing. The is a Hall-effect type sensor. The reads the gear teeth on the park gear, different than the teeth used for park function. The input to the PCM is used for shift scheduling, timing and operation and vehicle speed. The has bi-directional capability and has a digital output.
Engine Coolant Temperature (ECT) Sensor (Diesel Engine Vehicles)
The sensor is a 2 wire thermistor device in which resistance changes with temperature change. The resistance of the thermistor decreases as temperature increases, and the resistance increases as the temperature decreases. The varying resistance affects the voltage drop across the sensor and provides electrical signals to the PCM corresponding to temperature. The PCM uses this information to determine operation.
Cylinder Head Temperature (CHT) Sensor (Gasoline Engine Vehicles)
The sensor is a thermistor device in which resistance changes with temperature change. The resistance of the thermistor decreases as temperature increases, and the resistance increases as the temperature decreases. The varying resistance affects the voltage drop across the sensor and provides electrical signals to the PCM corresponding to temperature.
Intake Air Temperature (IAT) Sensor
The sensor is a thermistor device in which resistance changes with temperature change. The resistance of the thermistor decreases as temperature increases, and the resistance increases as the temperature decreases. The provides air temperature information to the PCM which is used to determine transmission line pressure and shift scheduling.
Accelerator Pedal Position (APP) Sensor
The sensor is mounted on the accelerator pedal on diesel applications. The detects the position of the accelerator pedal and sends this information as a voltage signal to the PCM. The PCM uses information to help determining line pressure, shift scheduling and 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 and intermediate shaft speed sensors are Hall-effect sensors requiring 12-volts for power and a ground source. The other 2 terminals at the sensor are for and intermediate shaft speed sensor signal output. The sensor detects teeth on the coast clutch input hub and the adjacent ring gear intermediate shaft speed sensors. Both read 30 teeth per revolution. The and intermediate shaft speed sensors are mounted externally on the transmission case toward the top on the driver's side. The and intermediate shaft speed sensors input to the PCM is a digital signal and is used to determine line pressure, shift scheduling, timing and operation.
Brake Pedal Position (BPP) Switch
Brake status comes from switch. The switch provides a voltage input to the PCM when the brake pedal is applied. The PCM uses this input to disengage the Torque Converter Clutch (TCC), speed control and auxiliary idle (if equipped).
PCM
Transmission operation is controlled by the PCM. Various sensors provide input information to the PCM. The PCM then provides output information solenoids which determine transmission operation.
Transmission Control Switch (TCS)
Tow/Haul
The Tow/Haul switch is a momentary contact switch located on the end of the transmission selector lever. When pressed, the Tow/Haul switch sends a signal to the PCM. The PCM then makes changes in shift scheduling and operation.
When Tow/Haul mode is activated the following occurs:
- All forward gears are available.
- Shifts occur at higher vehicle speeds to improve vehicle acceleration, reduce shift frequency and increase coast braking capability.
- TCC occurs at lower vehicle speeds to improve transmission cooling and efficiency.
- Upshifts are temporarily delayed during hill cresting to reduce transmission ratio hunting and to prepare for possible downshifts while descending a grade.
- Engine braking is provided in all forward gear positions, D, 3, 2 and 1.
- A PCM strategy, known as grade braking downshift automatically provides increased coast braking to assist the driver in maintaining a desired vehicle speed while descending a grade.
Default is Tow/Haul OFF.
Transmission Control Indicator Lamp (TCIL)
Tow/Haul
When the Tow/Haul switch has been pressed, the Transmission Control Indicator Lamp (TCIL), located near the end of the selector lever, will illuminate the graphics "Tow/Haul ON." Operation of the is controlled by the PCM to alert the driver that Tow/Haul mode has been activated. Pressing the again will turn off the TCIL. Turning off the engine will return the to the default position (Tow/Haul OFF).
The vehicle PCM may command steady illumination of the if certain faults are detected in monitored sensors, solenoids or apply components.
Transmission Control Switch (TCS)
Overdrive (O/D) OFF
The OFF is a momentary contact switch located on the end of the selector lever which is used along with the OFF indicator lamp Transmission Control Indicator Lamp (TCIL). When pressed, the OFF switch sends a signal to the PCM to only allow automatic upshifts that include 5th gear. O/D, or 6th gear, is disabled during OFF mode. Pressing the OFF switch again restores automatic upshifts from 1st through 6th gears.
Transmission Control Indicator Lamp (TCIL)
Overdrive (O/D) OFF
When the OFF switch has been pressed, the Transmission Control Indicator Lamp (TCIL), located near the end of the selector lever, close to the OFF switch, will illuminate the graphics "Overdrive OFF." Operation of the is controlled by the PCM to alert the driver that OFF mode has been activated. Pressing the again will turn off the and restore automatic upshifts, gears 1 through 6.
Each time the vehicle is started, the transmission will automatically turn off the and automatic upshifts, all forward gears 1 through 6 will be available.
The vehicle PCM may command steady illumination of the if certain faults are detected in monitored sensors, solenoids or apply components.
Transmission Solenoid Body Assembly
The PCM controls the transmission operation through the following:
- Seven Variable Force Solenoid (VFS)
- A sensor
- A manual valve
- An over-pressurization relief valve
All the above components are located on the solenoid body.
There is a solenoid dedicated to the function of each clutch. Line pressure and the each have their own solenoid. Four solenoids are directly proportional; the pressure output is directly proportional to the applied DC current. 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 sensor and for the sensor. The 24-pin bulkhead connector completes the serviceable harness assembly and has serviceable O-ring seals.
All 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 sensor twist-locks into the solenoid body. The sensor is a temperature-sensitive device called a thermistor. As the rises, the sensor resistance decreases. The PCM monitors the voltage across the sensor to determine TFT. The PCM uses the sensor signal as an input to determine cold and hot temperature shift and operation.
Line Pressure Control Solenoid A (PCA)
The 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 solenoid controls the line pressure circuits.
Torque Converter Clutch (TCC) Solenoid
The solenoid is a directly proportional Variable Force Solenoid (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 A (SSPCA), Shift Solenoid Pressure Control B (SSPCB), Shift Solenoid Pressure Control C (SSPCC), and Shift Solenoid Pressure Control E (SSPCE)
The intermediate (Shift Solenoid Pressure Control C (SSPCC)), low/reverse (Shift Solenoid Pressure Control E (SSPCE)) and (Shift Solenoid Pressure Control B (SSPCB)) clutches are each controlled by a directly proportional Variable Force Solenoid (VFS). The coast (Shift Solenoid Pressure Control A (SSPCA)) and the direct clutch (Shift Solenoid Pressure Control D (SSPCD)) 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 (Pressure Control Solenoid A (PCA)) solenoid and feedback to the pump main regulator valve. The relief valve controls line pressure spikes when cold. If this valve fails, concerns may be seen with the filter found in the solenoid body assembly.
Transmission Range (TR) Sensor
The sensor is an internally mounted sensor that includes the detent spring, rooster comb and bracket, located next to the solenoid body. The sensor is non adjustable and is not serviced independently. The components of the sensor are factory adjusted to each other and a new sensor must be installed as a calibrated assembly. The sensor contains electronic circuitry that provides the PCM a fixed frequency 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 sensor signal for engine functions (start, reverse lamps) and for Line Pressure Control (LPC), shift scheduling and operation.
Power Take-Off (PTO)
NOTICE: Failure to install the wire from the Powertrain Control Module (PCM) pin 322 to pin 294 will result in low line pressure leading to failure.
Some vehicles may be equipped with a Power Take-Off (PTO). During stationary operation in PARK or NEUTRAL, the torque converter is locked up when the is ON and the engine is operating at 1,200 rpm. The following chart shows the expected engine rpm and line pressure while driving with the in use.
