Transmission Electronic Control System
Transmission Electronic Control System
Electronic System Description
Transmission shift scheduling relies on the following components:
- Accelerator Pedal Position (APP)
- Engine rpm and acceleration
- Vehicle speed and acceleration
- Engine torque
- Torque converter state as defined by engine rpm
- Turbine Shaft Speed (TSS)
- Transmission Range (TR) sensor position
- Brake Pedal Position (BPP) status
- Cruise control status
- Transmission Control Switch (TCS) status
- Transmission Fluid Temperature (TFT)
- Engine Coolant Temperature (ECT)
- Power Take-Off (PTO) engaged signal
- Four-Wheel Drive (4WD) Low status
The PCM and its input/output network control the following transmission operations:
- Variable Force Solenoid (VFS) (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 certain input information from engine and driver 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 Computers and Control Systems Information 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. It also determines 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 transmission OSS (Output Shaft Speed) sensor is located on the extension housing. The OSS (Output Shaft Speed) sensor is a Hall-effect type sensor. The OSS (Output Shaft Speed) sensor reads the gear teeth on the park gear, which are different than the teeth used for the park function. The OSS (Output Shaft Speed) input to the PCM is used for shift scheduling and TCC (Torque Converter Clutch) operation. The OSS (Output Shaft Speed) sensor has bi-directional capability and has a digital output.
Engine Coolant Temperature (ECT) Sensor
The ECT (Engine Coolant Temperature) sensor is a 2-wire thermistor which changes resistance as temperature changes. The resistance of the sensor increases as engine temperature decreases and the voltage measured by the PCM increases. The PCM uses this information to determine TCC (Torque Converter Clutch) operation.
Intake Air Temperature (IAT) Sensor
The IAT (Intake Air Temperature) sensor is a thermistor which changes resistance as temperature changes. The resistance of the sensor decreases as the air temperature increases. The IAT (Intake Air Temperature) provides air temperature information to the PCM which is used to determine transmission line pressure and shift scheduling.
Accelerator Pedal Position (APP) Sensor
The APP (Accelerator Pedal Position) sensor is part of the accelerator pedal assembly. The APP (Accelerator Pedal Position) detects the position of the accelerator pedal and inputs this information as a voltage signal to the PCM. The PCM uses APP (Accelerator Pedal Position) sensor information in determining line pressure, shift scheduling and TCC (Torque Converter Clutch) operation. Failure of this sensor will cause the transmission to operate at high line pressure to avoid damage to the transmission. This high line pressure causes harsh upshifts and harsh engagements.
TSS (Turbine Shaft Speed) Sensor and Intermediate Shaft Speed Sensor
The TSS (Turbine Shaft Speed) and intermediate shaft speed sensors are both Hall-effect sensors requiring ignition voltage and a ground. The two other terminals at the sensor are TSS (Turbine Shaft Speed) /intermediate shaft speed sensor signal output. The TSS (Turbine Shaft Speed) sensor detects the teeth on the coast clutch input hub and the intermediate shaft speed sensor on the adjacent overdrive ring gear teeth. Both read 30 teeth per revolution. The TSS (Turbine Shaft Speed) /intermediate shaft speed sensor is mounted externally toward the top of the transmission case on the driver's side. The TSS (Turbine Shaft Speed) /intermediate shaft speed sensor input to the PCM is digital and is used to determine line pressure, shift scheduling and TCC (Torque Converter Clutch) operation.
Brake Pedal Position (BPP) Switch
Brake pedal position status comes from the BPP (Brake Pedal Position) switch. The BPP (Brake Pedal Position) switch sends a voltage signal to the PCM when the brake pedal is applied. The PCM uses this input to disengage the TCC (Torque Converter Clutch), speed control and auxiliary idle (if equipped).
Powertrain Control Module
The operation of the transmission is controlled by the PCM. Various sensors provide information to the PCM. The PCM controls actuators which determine transmission operation.
Transmission Control Switch (TCS)
The TCS (Transmission Control Switch) or (O/D (Overdrive) OFF switch) is a momentary contact switch located on the end of the selector lever. When pressed, the O/D (Overdrive) OFF switch sends a signal to the PCM allowing automatic upshifts that include 5th gear. Overdrive or 6th gear, is disabled during O/D (Overdrive) OFF mode. Pressing the O/D (Overdrive) OFF button again restores automatic upshifts from 1st through 6th gears or the next ignition cycle.
Transmission Control Indicator Lamp (TCIL)
The TCIL (Transmission Control Indicator Lamp), located in the Instrument Cluster (IC), will illuminate the graphic O/D (Overdrive) OFF when the O/D (Overdrive) OFF switch is pressed. Operation of the TCIL (Transmission Control Indicator Lamp) is controlled by the PCM to alert the driver that the O/D (Overdrive) OFF mode is active. Pressing the O/D (Overdrive) OFF switch again will turn off the TCIL (Transmission Control Indicator Lamp) and restore automatic upshifts from 1st through 6th gears or the next ignition cycle.
The PCM may command the TCIL (Transmission Control Indicator Lamp) on if certain transmission DTCs are detected.
Four-Wheel Drive (4WD) Low Switch
The 4WD (Four-Wheel Drive) Low switch sends a ground signal to the IC (Instrument Cluster) when the vehicle is in 4WD (Four-Wheel Drive) Low. The PCM then receives a 4WD (Four-Wheel Drive) Low status from the IC (Instrument Cluster) and adjusts the transmission shift schedule accordingly.
Transmission Solenoid Body Assembly
The PCM controls the transmission operation through:
- seven VFS (Variable Force Solenoid).
- a TFT (Transmission Fluid Temperature) 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 TCC (Torque Converter Clutch) each have their own solenoid. Four solenoids are directly proportional; the pressure output is directly proportional to the applied direct current. Three solenoids are inversely proportional; the pressure output is inversely proportional to the applied direct current.
Solenoids are keyed to prevent misassembly. There are separate connectors for the TFT (Transmission Fluid Temperature) sensor and the TR (Transmission Range) switch. The 24-pin connector completes the serviceable harness assembly and has serviceable O-rings.
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 TFT (Transmission Fluid Temperature) sensor twist-locks into the solenoid body. The TFT (Transmission Fluid Temperature) is a temperature-sensitive device called a thermistor. As the transmission fluid temperature rises, the TFT (Transmission Fluid Temperature) sensor resistance decreases. The PCM monitors the voltage across the TFT (Transmission Fluid Temperature) sensor to determine transmission fluid temperature. The PCM uses the TFT (Transmission Fluid Temperature) signal to determine hot and cold temperature shift scheduling and TCC (Torque Converter Clutch) operation.
Pressure Control Solenoid A (PCA)
The Pressure Control Solenoid A (PCA) is an inversely proportional 3-port device. The pressure output is inversely proportional to the applied direct current supplied from the PCM through an electronically controlled driver, which varies the current between 0 and 1 amp. The PCA (Pressure Control Solenoid A) solenoid controls the line pressure circuits.
Torque Converter Clutch (TCC) Solenoid
The TCC (Torque Converter Clutch) solenoid is a directly proportional VFS (Variable Force Solenoid). The pressure output of this 3-port device is proportional to the applied direct current supplied from the PCM through an electronically controlled driver which varies the current between 0 and 1 amp.
Shift Solenoid Pressure Control Solenoids
The intermediate Shift Solenoid Pressure Control C (SSPCC), low/reverse Shift Solenoid Pressure Control E (SSPCE) and overdrive Shift Solenoid Pressure Control B (SSPCB) clutches are each controlled by a directly proportional VFS (Variable Force Solenoid). 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 (Variable Force Solenoid). 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 PCA (Pressure Control Solenoid A) and feedback to the pump main regulator valve. The line pressure relief valve controls line pressure spikes when cold. If this valve fails, concerns with the filter found in the solenoid body assembly may be seen.
Transmission Range (TR) Sensor Assembly
The TR (Transmission Range) 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 (Transmission Range) sensor are factory adjusted and the TR (Transmission Range) sensor must be installed as a calibrated assembly. The TR (Transmission Range) sensor contains electronic circuitry that provides the PCM a fixed frequency duty cycle for each of the various positions of the manual lever (PARK, REVERSE, NEUTRAL, (D), M3, M2 and M1) to the PCM. The PCM uses the TR (Transmission Range) sensor signal for engine start, reverse lamps and for line pressure control, shift scheduling and TCC (Torque Converter Clutch) operation.
Power Take-Off (PTO)
Vehicles may come equipped with a PTO (Power Take-Off). During stationary operation in PARK or NEUTRAL, the torque converter is locked up when the PTO (Power Take-Off) is ON and the engine operates at 1200 rpm. The following schedule shows expected engine rpm and line pressure while driving with the PTO (Power Take-Off) in use.
