Transmission Electronic Control System
Transmission Electronic Control SystemElectronic System Description
The Powertrain Control Module (PCM) and its input/output network control the following transmission operations:
^ shift timing
^ line pressure (shift feel)
^ torque converter clutch
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.
In addition, the PCM receives input signals from certain transmission-related sensors and switches. The PCM also uses these signals when determining transmission operating strategy.
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 hydraulic solenoids to control transmission operation.
The following provides a brief description of each of the sensors and actuators used to control transmission operation.
Mass Air Flow (MAF) Sensor
The Mass Air Flow Sensor (MAF) measures the mass of air flowing into the engine. The MAF sensor output signal is used by the Powertrain Control Module (PCM) to calculate injector pulse width. For transmission strategies the MAF sensor is used to regulate electronic pressure control EPC, shift and torque converter clutch scheduling.
Powertrain Control Module (PCM)
The operation of the transmission is controlled by the Powertrain Control Module (PCM). Many input sensors provide information to the PCM. The PCM then controls actuators which determine transmission operation.
Transmission Control Switch (TCS) and Transmission Control Indicator Lamp (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 energizes the Transmission Control Indicator Lamp (TCIL) when the switch is off. The TCIL indicates overdrive cancel mode activated (lamp on) and Electronic Pressure Control (EPC) circuit shorted (lamp flashing) or a monitored sensor failure.
Output Shaft Speed (OSS) Sensor
The Output Shaft Speed (OSS) sensor is a magnetic pickup, located at the output shaft ring gear, that sends a signal to the powertrain control module to indicate transmission output shaft speed. The OSS is used for torque converter clutch control, shift scheduling and to determine electronic pressure control.
Digital Transmission Range (TR) Sensor
The digital Transmission Range (TR) sensor is located on the outside of the transmission at the manual lever. The digital TR sensor completes the start circuit in PARK and NEUTRAL, the back-up lamp circuit in REVERSE and the neutral sense circuit (4x4 only) in NEUTRAL. The digital TR sensor also opens and closes a set of four switches that are monitored by the powertrain control module (PCM) to determine the position of the manual lever (P. R. N. D, 2, 1).
Transmission Fluid Temperature (TFT) Sensor
The Transmission Fluid Temperature (TFT) sensor is located on the lead frame assembly near the shift solenoids on the main control valve body. It is a temperature sensitive device called a thermistor. It sends a voltage signal to the PCM. The voltage signal varies with transmission fluid temperature. The PCM uses this signal to determine whether a cold start shift schedule is necessary. The shift schedule is compensated when the transmission fluid temperature is cold. The PCM also inhibits (TCC) operation at low transmission fluid temperatures and corrects electronic pressure control.
Vehicle Speed Sensor (VSS)
The Vehicle Speed Sensor (VSS) is model dependent. Possible sources of vehicle speed input arc, Anti-Lock Brake Sensor (ABS), a gear-driven Vehicle Speed Sensor (VSS), or the transmission Output Shaft Speed (OSS) sensor. On 4x4 applications with a manual shift transfer case, the transfer case speed sensor is the source of vehicle speed. The VSS signal is either an AC signal whose frequency changes with vehicle speed, or an SCP data message depending on the source Some vehicles have both. The vehicle speed signal is an input to various vehicle sub-systems such as the Powertrain Control Module (PCM), instrument cluster (speedometer and odometer), speed control systems, etc. The vehicle speed source must be operational to enter output state control mode for diagnostics.
Electronic Pressure Control (EPC) Solenoid
The Electronic Pressure Control (EPC) solenoid regulates transmission pressure. EPC valve pressure is used to control line pressure.
Shift Solenoid-SSA, SSB
Two on/off shift solenoids provide gear selection of first through fourth gears by controlling the pressure to the three shift valves. One unit containing the two shift solenoids is located in the main control valve body. The shift solenoids are two-way normally open style.
Solenoid Operation Chart
a When a manual pull-in occurs above a calibrated speed, the transmission will downshift from the higher gear until the vehicle speed drops below this calibrated speed.
EC = Electronically Controlled.
HD = Hydraulically Disabled.
Torque Converter Clutch (TCC) Solenoid
The Torque Converter Clutch (TCC) solenoid is used to control the apply and release of the TCC.
4x4 Low (4x4L) Switch
The 4x4 Low (4x4L) range switch is located on the transfer case cover. It provides an indication of when the 4x4 transfer case gear system is in the low range. The PCM then modifies shift schedule for 4x4L operation.
Brake Pedal Position (BPP) Switch
The Brake Pedal Position (BPP) switch tells the Powertrain Control Module (PCM) when the brakes are applied. The torque converter clutch disengages when the brakes are applied. The BPP switch closes when the brakes are applied and opens when they are released.
Electronic Ignition (EI) System
The electronic ignition consists of a crankshaft position sensor, two four tower ignition coils and the Powertrain Control Module (PCM). The ignition control module operates by sending crankshaft position information from the crankshaft position sensor to the ignition control module. The ignition control module generates a Profile Ignition Pickup (PIP) signal (engine rpm) and sends it to the PCM. The PCM uses PIP signal in the transmission strategy, Wide-Open Throttle (WOT) shift control, torque converter clutch control and EPC pressure.